70 questions — 45 objective (1 mark), 13 short (5 marks), 12 long (10 marks). Every answer is checked against the 2014 BEE guidebook and carries its book section reference plus an explanation. ▶ Practice this chapter interactively (timer, read-aloud, progress saving).
Objective questions (1 mark) — 45
📖 §10.14 Energy Performance Index (EPI)
1. AI PRACTICE: The Energy Performance Index (EPI) of a building is defined as which of the following?
Annual energy consumption / carpet area
Annual energy consumption / built-up area
HVAC energy / built-up area
Annual energy consumption / number of occupants
Answer: B) Annual energy consumption / built-up area
Confirmed vs Book-3 §10.14 — EPI = total annual building energy consumption / BUILT-UP area, in kWh/m2/year. The book defines built-up area as carpet area + area covered by wall thickness + balconies etc., excluding basement and other areas used for parking (included if the basement is used for anything else). (a) carpet area is the book's own trap option; (c) is wrong because ALL building energy is counted, not just HVAC and lighting.
Source: AI practice
📖 §10.14 Star rating of buildings
2. AI PRACTICE: Under the star rating scheme, which statement is correct regarding EPI and star rating?
Higher EPI means more stars
Lower EPI means more stars
EPI has no relation to the star rating
The star rating is fixed by connected load, not by EPI
Answer: B) Lower EPI means more stars
Confirmed vs Book-3 §10.14 — Office buildings are rated on a 1-5 Star scale with 5-Star the most efficient, and the scale is INVERSE to EPI: for a composite-zone building with more than 50% air-conditioned area the band is 190-90 kWh/m2/yr, so an EPI below 90 earns 5 Stars while 165-190 earns 1 Star. (a) is the direct trap. Bands are set per climatic zone and per percentage of air-conditioned space, and the label is valid for 5 years.
Source: AI practice
📖 §10.2 Building definition – ECBC applicability
3. AI PRACTICE: As per the EC Act amendment, ECBC applies to a commercial building having a connected load of at least how much, OR a contract demand of at least how much?
50 kW or 60 kVA
500 kW or 600 kVA
100 kW or 120 kVA
1000 kW or 1200 kVA
Answer: C) 100 kW or 120 kVA
Confirmed vs Book-3 §10.2 — The Energy Conservation (Amendment) Act 2010 defines 'building' as a structure having a connected load of 100 kW OR a contract demand of 120 kVA and above, used or intended for commercial purposes. Memorise the pair 100 kW / 120 kVA, and note the criteria are alternatives (OR), not cumulative. (b) 500 kW / 600 kVA is the book's own trap option in its objective questions.
Source: AI practice
📖 §10.5 Solar Heat Gain Coefficient (SHGC)
4. AI PRACTICE: A glazing receives incident solar radiation of 700 W/m2 and has an SHGC of 0.30. What is the solar heat gain through the glazing?
210 W/m2
230 W/m2
700 W/m2
2333 W/m2
Answer: A) 210 W/m2
Confirmed vs Book-3 §10.5 — SHGC is the ratio of solar heat gain passing through the fenestration to the total incident solar radiation, so heat gain = SHGC x incident = 0.30 x 700 = 210 W/m2. (d) 2333 W/m2 comes from dividing by the SHGC; (c) 700 W/m2 would need SHGC = 1, i.e. no glazing at all. SHGC counts both directly transmitted solar heat and absorbed heat that is re-radiated, conducted or convected inward.
Source: AI practice
📖 §10.5 Window-Wall Ratio (WWR)
5. AI PRACTICE: The Window-to-Wall Ratio (WWR) is defined as which of the following?
Skylight area / gross exterior roof area
Vertical fenestration area / gross exterior wall area
Glazed vision area / gross conditioned floor area
Gross exterior wall area / vertical fenestration area
Answer: B) Vertical fenestration area / gross exterior wall area
Confirmed vs Book-3 §10.5 — WWR is the ratio of vertical fenestration area to gross exterior wall area, the wall area being measured horizontally from the exterior surface and vertically from the top of the floor to the bottom of the roof. (d) simply inverts the ratio and (a) is the skylight-roof ratio, a different ECBC parameter. WWR matters because the daylighting check uses Effective Aperture EA = VLT x WWR.
Source: AI practice
📖 §10.5 Effective aperture of glazing
6. AI PRACTICE: A facade has a WWR of 0.5 and a glazing VLT of 0.22. Does the effective aperture comply with the ECBC daylighting rule (EA >= 0.1)?
EA = 0.11, complies
EA = 0.09, does not comply
EA = 0.72, complies
EA = 0.05, does not comply
Answer: A) EA = 0.11, complies
Confirmed vs Book-3 §10.5 — Effective Aperture EA = VLT x WWR = 0.22 x 0.5 = 0.11; since EA is greater than 0.1 the glazing complies with ECBC. The book's two cases fix the cut-off: WWR 0.4 x VLT 0.26 = 0.104 complies, WWR 0.6 x VLT 0.15 = 0.09 does not. (c) 0.72 comes from adding the two figures instead of multiplying them.
Source: AI practice
📖 §10.5 Cool roof (ECBC 4.3.1.1)
7. AI PRACTICE: Which of the following is the correct definition of a cool roof as per ECBC?
A roof that absorbs and stores heat
A roof with high solar reflectance and high thermal emittance
A roof with low reflectance and low emittance
A roof made only of concrete
Answer: B) A roof with high solar reflectance and high thermal emittance
Confirmed vs Book-3 §10.5 — A cool roof is defined by its ability to reflect and reject heat: it must have BOTH high solar reflectance AND high thermal emittance. ECBC 4.3.1.1 as quoted in the book requires a minimum solar reflectance of 0.7 and an initial emittance of not less than 0.75. (a) and (c) describe a conventional roof, which absorbs heat and transfers it to the building below. Related identity: reflectance + absorptance = 1, both rated on a 0 to 1 scale.
Source: AI practice
📖 §10.5 Fenestration
8. AI PRACTICE: Which of the following is NOT considered fenestration?
A window
A skylight
A valve
A ventilator
Answer: C) A valve
Confirmed vs Book-3 §10.5 (and the book's own objective question 7) — Fenestration systems are windows, skylights, ventilators and doors that are more than one-half glazed, i.e. all light-admitting openings in the envelope including their frames. A valve is a piping fitting, not an opening in the building envelope. Linked definitions: a skylight is a fenestration surface sloping less than 60 degrees from the horizontal; all other fenestration is 'vertical fenestration'.
9. AI PRACTICE: In the ECBC envelope trade-off compliance approach, which metric is used (Appendix D)?
Energy Performance Index (EPI)
Envelope Performance Factor (EPF)
Lighting Power Density (LPD)
Visible Light Transmittance (VLT)
Answer: B) Envelope Performance Factor (EPF)
Confirmed vs Book-3 §10.4/§10.5 — The Envelope Trade-Off approach uses the Envelope Performance Factor (EPF), computed for both the proposed and the baseline design as per Appendix D of ECBC; the proposed building's EPF must be equal to or better than the baseline. Trade-offs are permitted only WITHIN the envelope components (roof, walls, fenestration). (a) EPI belongs to the BEE star-rating scheme (§10.14), not to ECBC compliance; energy simulation (Appendix B) is the Whole Building Performance route, not the trade-off route.
Source: AI practice
📖 §10.11 Uninterruptible power supply
10. AI PRACTICE: In a UPS, which component converts DC back to AC?
Converter (rectifier)
Battery
Inverter
Static switch
Answer: C) Inverter
Confirmed vs Book-3 §10.11 (and the book's own objective question 10) — The components of a UPS are a converter (AC to DC), a battery, an inverter (DC to AC) and monitor/control hardware and software; the inverter is the DC-to-AC stage that feeds the load. (a) the converter/rectifier performs the opposite conversion and (d) a static switch only transfers the load between sources. An on-line (double conversion) UPS runs AC-DC-AC continuously; off-line/line-interactive types are more efficient but transfer on a dip.
Source: AI practice
📖 §10.14 EPI bands and star rating
11. AI PRACTICE: A composite-zone office (A/C area >50% of built-up, band 190-90) has a built-up area of 20,000 m2 and an annual energy consumption of 1,600,000 kWh. What is its EPI and likely star rating?
80 kWh/m2/yr, 5-Star
80 kWh/m2/yr, 1-Star
125 kWh/m2/yr, 5-Star
200 kWh/m2/yr, 1-Star
Answer: A) 80 kWh/m2/yr, 5-Star
Confirmed vs Book-3 §10.14 — EPI = annual energy / built-up area = 16,00,000 / 20,000 = 80 kWh/m2/year. For a composite-zone building with more than 50% air-conditioned area the band is 190-90, and the book states a building gets 5 Stars if its EPI falls below 90 (1 Star if it is between 165 and 190). (b) inverts the direction of the scale — lower EPI always means MORE stars; (c) and (d) come from using a wrong divisor.
Source: AI practice
📖 §10.5 Thermal emittance (emissivity)
12. AI PRACTICE: Thermal emittance (emissivity) of a material is defined as which ratio?
Solar energy reflected by the material / total solar energy incident on it
Energy radiated by the material / energy radiated by a black body at the same temperature
Visible light transmitted by the material / visible light incident on it
Heat flow through the material / temperature difference across it
Answer: B) Energy radiated by the material / energy radiated by a black body at the same temperature
Confirmed vs Book-3 §10.5 — Emissivity (thermal emittance) is the ratio of energy radiated by a particular material to the energy radiated by a black body at the same temperature; it is dimensionless, with e = 1 for a true black body and e < 1 for any real object. (a) is solar reflectance, (c) is visible light transmittance (VLT) and (d) describes the U-factor. In general the duller and blacker a material, the closer its emissivity is to 1; the more reflective it is, the lower its emissivity.
Source: AI practice
📖 §10.5 Building envelope — Solar Heat Gain Coefficient (SHGC)
13. What is the Solar Heat Gain Coefficient (SHGC) used for in building energy analysis?
To measure light transmittance
To measure the heat gain through fenestration due to solar radiation
To measure air leakage through windows
To measure the thermal emittance of roofing materials
Answer: B) To measure the heat gain through fenestration due to solar radiation
Confirmed vs Book-3 §10.5 — SHGC is the ratio of solar heat gain that passes through fenestration to the total incident solar radiation on it (directly transmitted + absorbed-and-re-radiated/conducted/convected inward). Option (a) is VLT (visible portion only), (c) is infiltration/weather-stripping and (d) is thermal emittance of roofs, not SHGC.
Source: Sep 2024
📖 §10.14 Star rating of buildings — Energy Performance Index (EPI)
14. Energy Performance Index is the ratio of total building annual energy consumption to ------
Carpet area
Built up area
roof area
Windows and Walls area
Answer: B) Built up area
Confirmed vs Book-3 §10.14 — EPI (kWh/sq m/year) = total building annual energy consumption ÷ built-up area. Built-up area = carpet area + wall-thickness area + balconies (excluding parking basements), so carpet area (a) is the tempting wrong choice; roof or window/wall areas are never the denominator.
Source: Sep 2024
📖 §10.2 Building definition — Energy Conservation (Amendment) Act 2010
15. The Energy Conservation Act applies to buildings with connected load:
All HT connections
Commercial building having ≥ 100 kW
Residential buildings only
Government buildings having ≥ 100 kW
Answer: B) Commercial building having ≥ 100 kW
Confirmed vs Book-3 §10.2 — A 'building' under the EC Act is one with a connected load of 100 kW or contract demand of 120 kVA and above, used or intended for commercial purposes. The Act is not restricted to HT connections, residential or government buildings.
16. The Envelope Performance Factor (EPF) in ECBC is used to:
Compare energy efficiency of proposed and baseline building designs
Determine cooling tower sizing
Calculate lighting power density
Measure indoor air quality
Answer: A) Compare energy efficiency of proposed and baseline building designs
Confirmed vs Book-3 §10.5 — Under the Envelope Trade-off approach, the Envelope Performance Factor is calculated for the proposed design and the baseline design; the proposed building's EPF must be equal to or better than the baseline. It has nothing to do with cooling-tower sizing, LPD or indoor air quality.
Source: Sep 2025
📖 §10.2 Building definition — Energy Conservation (Amendment) Act 2010
17. EC Act covers buildings having a connected load of
500 kW and above
500 kVA and above
100 kW and above
all HT connection buildings
Answer: C) 100 kW and above
Corrected (was a: 500 kW and above) — Book-3 §10.2: the EC (Amendment) Act 2010 defines a 'building' as one having a connected load of 100 kW or a contract demand of 120 kVA and above, used for commercial purposes. 500 kW / 500 kVA are distractors; 'all HT connections' is not a criterion.
Source: Book EOC
📖 §10.8 ECBC guidelines on lighting — Lighting Power Density (LPD)
18. LPD in ECBC refers to
low power density
Lux power density
Lighting power density
Low power demand
Answer: C) Lighting power density
Confirmed vs Book-3 §10.8 — LPD stands for Lighting Power Density, an indicator of lighting power in watts per square metre (W/m²), derived by the Building Area Method or the Space Function Method. The other expansions are not ECBC terms.
Source: Book EOC
📖 §10.14 Star rating of buildings — Energy Performance Index (EPI)
19. Energy performance index (EPI) kWh/m2/yr is calculated based on
total building annual energy consumption / built up area
total building annual energy consumption / Carpet area
total building annual energy consumption for HVAC & lighting / built up area
none of the above
Answer: A) total building annual energy consumption / built up area
Confirmed vs Book-3 §10.14 — EPI = total building annual energy consumption ÷ built-up area (kWh/m²/yr). It covers ALL building energy (not HVAC & lighting only) and uses built-up area, not carpet area.
Source: Book EOC
📖 §10.3 ECBC — five climatic zones (Figure 10.1)
20. Which of the following is not a climate zone as per ECBC classification?
Hot - dry
Warm - humid
Cold
Cold humid
Answer: D) Cold humid
Confirmed vs Book-3 §10.3 — For ECBC, India is divided into five climatic zones: Composite, Hot-Dry, Warm-Humid, Moderate (Temperate) and Cold. 'Cold-humid' does not exist in the ECBC classification.
Source: 18th Exam
📖 §10.5 Passive solar design — Cool roof
21. A cool roof
absorbs heat
reflects heat
transmits heat
conducts heat
Answer: B) reflects heat
Confirmed vs Book-3 §10.5 — A cool roof is defined by its ability to reflect and reject heat: high solar reflectance (ECBC min 0.7) and high emittance (min 0.75). A roof that absorbs, transmits or conducts heat is the opposite of a cool roof.
Source: Book EOC
📖 §10.5 Building envelope — Solar Heat Gain Coefficient (SHGC)
22. SHGC in building envelope energy analysis is
solar heat gain coefficient
solar hot water gain coefficient
standard heat gain coefficient
standard hot glass coefficient
Answer: A) solar heat gain coefficient
Confirmed vs Book-3 §10.5 — SHGC = Solar Heat Gain Coefficient, the ratio of solar heat gain passing through fenestration to total incident solar radiation. It has nothing to do with hot water or 'standard' coefficients.
Source: Book EOC
📖 §10.5 Building envelope — Fenestration definition
23. Which one is not a fenestration?
windows
skylights
ventilators
valves
Answer: D) valves
Confirmed vs Book-3 §10.5 — Fenestration systems include windows, skylights, ventilators and doors that are more than one-half glazed, i.e. all openings in the envelope that let in light. A valve is a piping component, not an envelope opening.
Source: Book EOC
📖 §10.5 Building envelope — Visible Light Transmittance (VLT)
24. The ratio of daylight passing through the glazing to the light passing through perfectly transmissive glazing is called
visible light transmittance
SHGC
luminance index
glazing coefficient
Answer: A) visible light transmittance
Confirmed vs Book-3 §10.5 — VLT is the ratio of light passing through the glazing to light passing through perfectly transmissive glazing; it concerns only the visible spectrum and matters for daylighting. SHGC (b) is the ratio for ALL solar radiation, not just daylight.
Source: Book EOC
📖 §10.14 Star rating — BPO buildings, Average Annual hourly EPI (AAhEPI)
25. The unit of AAhEPI is
kWh/m2/yr
m2 x kWh/hr
(Wh/sqm)/hr
m2/Wh/yr
Answer: C) (Wh/sqm)/hr
Corrected (was a: kWh/m2/yr) — Book-3 §10.14: AAhEPI (Average Annual hourly Energy Performance Index) used for BPO star rating is expressed in (Wh/sqm)/hr = [EPI ÷ (daily hours × days/week × 52)] × 1000. kWh/m²/yr (a) is the unit of ordinary EPI — the tempting wrong option.
Source: Book EOC
📖 §10.11 Uninterruptible power supply — components
26. In a UPS the conversion from DC to AC is carried out by
converter
charger
battery
inverter
Answer: D) inverter
Confirmed vs Book-3 §10.11 — UPS components are a converter/charger (AC to DC), battery, inverter (DC to AC) and monitor/control hardware. The inverter performs DC→AC; the converter/charger does AC→DC and the battery only stores energy.
Source: Book EOC
📖 §10.14 Star rating of buildings — EPI unit
27. The Energy Performance Index (EPI) of a building as per ECBC and the Energy Conservation Act, 2001 is:
kWh per square meter per year
kWh per square meter
kW per square meter
kWh per year
Answer: A) kWh per square meter per year
Confirmed vs Book-3 §10.14 — EPI is the specific energy usage of a building in kWh per square metre per year (annual energy ÷ built-up area). kWh/m² alone lacks the time base and kW/m² is a power density, not energy.
Source: 14th Exam
📖 §10.5 Building envelope — SHGC (Figure 10.4)
28. The Solar Heat Gain Co-efficient (SHGC) of a window of a building is 0.30. This means
The window allows 70% of the sun's heat to pass through into interior of the building
The window allows 30% of the sun's heat to pass through into the building interior
70% of the sun's heat is incident on the window
The window reflects back to exterior a minimum of 30 % of the sun's heat
Answer: B) The window allows 30% of the sun's heat to pass through into the building interior
Confirmed vs Book-3 §10.5 — SHGC is the fraction of incident solar radiation that passes through the fenestration as heat; SHGC 0.30 means 30% of the sun's heat enters the interior (Figure 10.4: SHGC 0.39 → 39% transmitted). The remaining 70% is reflected or rejected, not 'incident', so (c)/(d) are wrong.
Source: Mar 2021
📖 §10.8 ECBC guidelines on lighting — Building Area Method
29. As per the building area method given in ECBC, compute the lighting power allowance; given the allowed LPD is 12 watt per square meter and enclosed office area is 500 square meter.
6 kW
4.16 kW
6 W
4.16 W
Answer: A) 6 kW
Confirmed vs Book-3 §10.8 — Interior lighting power allowance = gross lighted floor area × allowed LPD = 500 m² × 12 W/m² = 6000 W = 6 kW (same method as the book's hotel example: 1000 × 10.8 × 4 = 43,200 W). Watch the unit: 6 W (c) is a 1000× slip.
30. As per ECBC compute the Effective Aperture (EA); given Window Wall Ratio (WWR) is 0.40 and Visible Light Transmittance (VLT) is 0.25.
0.10
0.65
0.33
0.15
Answer: A) 0.10
Confirmed vs Book-3 §10.5 — Effective Aperture = VLT × WWR = 0.25 × 0.40 = 0.10 (light-admitting potential of the glazing). The book's own example uses 0.4 × 0.26 = 0.104 (> 0.1, complies). Adding (0.65) or dividing (1.6/0.625) are the tempting errors.
Source: 17th Sep-2016
📖 §10.14 Star rating of buildings — EPI unit
31. The Energy Performance Index (EPI) of a building as per Energy Conservation Building Code (ECBC) and as defined in the Energy Conservation Act, 2001 is:
kWh per square meter per year
kWh per square meter
kW per square meter
kWh per year
Answer: A) kWh per square meter per year
Confirmed vs Book-3 §10.14 — EPI = total annual building energy consumption ÷ built-up area, expressed in kWh/sq m/year. Options without 'per year' or in kW are incomplete/incorrect.
Source: 19th Exam
📖 §10.2 Building definition — Energy Conservation (Amendment) Act 2010
32. Energy Conservation Act covers buildings having a connected load of
100 kW and above
100 kVA and above
500 kW and above
All buildings with HT connection
Answer: A) 100 kW and above
Confirmed vs Book-3 §10.2 — The EC Act covers commercial buildings with a connected load of 100 kW or contract demand of 120 kVA and above. 500 kW (c) and 100 kVA (b) are distractors; HT connection is not the criterion.
Source: 19th Exam
📖 §10.5 Building envelope — SHGC (Figure 10.4)
33. The Solar Heat Gain Co-efficient (SHGC) of a window of a building is 0.30. This means that ___________
the window allows 70% of the sun's heat to pass through into interior of the building
the window allows 30% of the sun's heat to pass into the building interior
70% of the sun's heat is incident on the window
the window reflects back to exterior a minimum of 30% of the sun's heat
Answer: B) the window allows 30% of the sun's heat to pass into the building interior
Confirmed vs Book-3 §10.5 — SHGC is the ratio of solar heat gain through fenestration to total incident solar radiation, so SHGC 0.30 means 30% of the sun's heat passes into the building interior. It does not state what is reflected (d) or what is incident (c).
Source: Mar 2021 (Set B)
📖 §10.14 Star rating of buildings — Energy Performance Index (EPI)
34. Energy performance index (EPI) kWh/m2/yr is the ratio of total building annual energy consumption to __________.
Built up area
Carpet area
Roof Area
Window and Wall Area
Answer: A) Built up area
Confirmed vs Book-3 §10.14 — EPI (kWh/m²/yr) = total building annual energy consumption ÷ built-up area. Built-up area = carpet area + wall thickness + balconies (parking basements excluded); carpet area (b) is the classic wrong pick.
Source: Sep 2019
📖 §10.8 ECBC guidelines on lighting — Building Area Method (worked example)
35. A hotel building has four floors each of 1000 m2 area. If the Lighting Power Density (LPD) is 10.8 W/m2, the interior lighting power allowance for the hotel building is
10800 W
21600 W
43200 W
none of the above
Answer: C) 43200 W
Confirmed vs Book-3 §10.8 — This is the book's worked example: interior lighting power allowance = (1000 m² × 10.8 W/m²) × 4 floors = 43,200 W. 10,800 W (a) is one floor only; 21,600 W (b) is two floors.
Source: 11th Feb-2011
📖 §10.2 Building definition — Energy Conservation (Amendment) Act 2010
36. ECBC code is applicable to commercial buildings having connected load of ________.
100 kW
500 kW
250 kW
1000 kW
Answer: A) 100 kW
Confirmed vs Book-3 §10.2 — ECBC/EC Act applies to commercial buildings with connected load of 100 kW or contract demand of 120 kVA and above. 250, 500 and 1000 kW are distractors.
37. When the evaporation of water from a wet substance at atmospheric condition is zero, it indicates ________.
RH is 0%
RH is 100%
wet bulb temperature is greater than dry bulb temperature
none of the above
Answer: B) RH is 100%
Confirmed vs Book-3 Ch4 psychrometrics — Evaporation from a wet surface stops only when the surrounding air is saturated, i.e. relative humidity is 100% (WBT = DBT = dew point). At RH 0% evaporation would be maximum, and WBT can never exceed DBT.
38. As per Energy Conservation Building Code, compute the Effective Aperture (EA) given that Window Wall Ratio (WWR) is 0.40 and Visible Light Transmittance (VLT) is 0.25.
0.1
1.6
0.65
0.625
Answer: A) 0.1
Confirmed vs Book-3 §10.5 — EA = VLT × WWR = 0.25 × 0.40 = 0.1, exactly the ECBC compliance threshold (book: EA > 0.1 complies, EA < 0.1 does not). 1.6 and 0.625 come from wrongly dividing; 0.65 from adding.
Source: Mar 2021
📖 §10.14 Star rating — BPO buildings, Average Annual hourly EPI (AAhEPI)
39. The unit of AAhEPI is given by
kWh/m2/yr
m2 × kWh/hr
(Wh/m2)/hr
m2/Wh/yr
Answer: C) (Wh/m2)/hr
Confirmed vs Book-3 §10.14 — AAhEPI (Average Annual hourly Energy Performance Index, used for BPO/call-centre star rating) is in (Wh/sqm)/hr: [EPI ÷ (daily hours × days/week × 52 weeks)] × 1000. kWh/m²/yr (a) is the unit of ordinary EPI, the tempting wrong option. (Option b repaired from garbled 'm2/a kWh/hr'; question acronym corrected from 'AhhEPI'.)
40. As per Energy Conservation Building Code, compute the Effective Window Wall Ratio (EWA) given that Window Wall Ratio (WWR) is 0.40 and Visible Light Transmittance (VLT) is 0.25 ___________
0.1
1.6
0.65
0.625
Answer: A) 0.1
Confirmed vs Book-3 §10.5 — The 'effective' window-wall ratio for daylighting is the Effective Aperture = VLT × WWR = 0.25 × 0.40 = 0.1 (light-admitting potential of the glazing system). Division (1.6, 0.625) or addition (0.65) are the errors to avoid.
Source: Mar 2021 (Set B)
📖 Ventilation by air changes (Book-3 Ch9 DG set room / Ch4 HVAC): flow = room volume × ACH
41. In an engine room 15 m long, 10 m wide and 4 m high, ventilation requirement for 20 air changes/hr is _____ m³/hr
30
3000
12000
none of the above
Answer: C) 12000
Confirmed vs Book-3 (ventilation rule) — Room volume = 15 × 10 × 4 = 600 m³; at 20 air changes per hour the ventilation air required = 600 × 20 = 12,000 m³/hr. 30 (a) is the sum of dimensions and 3000 (b) is a slip.
Source: Jul 2022
📖 §10.5 Building envelope — SHGC (Figure 10.4)
42. The Solar Heat Gain Coefficient (SHGC) of window of a building is 0.30. This means that
The window reflects back to exterior a minimum of 30 % of the sun's heat
The window allows 30 % of the sun's heat to pass through into the building interior
70 % of the sun's heat is reflected on the window
The window allows 70 % of the sun's heat to pass through into interior of the building
Answer: B) The window allows 30 % of the sun's heat to pass through into the building interior
Confirmed vs Book-3 §10.5 — SHGC = solar heat gain through fenestration ÷ total incident solar radiation; SHGC 0.30 means 30% of the sun's heat passes into the interior. The statement says nothing about the reflected share, so (a)/(c) are wrong and (d) inverts the ratio.
Source: Jul 2022
📖 §10.14 Star rating of buildings — Energy Performance Index (EPI)
43. Energy performance index is calculated based on
total building annual energy consumption /built up area
total building annual energy consumption /carpet area
total building annual energy consumption for HVAC and lighting /carpet area
none of the above
Answer: A) total building annual energy consumption /built up area
Confirmed vs Book-3 §10.14 — EPI = total building annual energy consumption ÷ built-up area (kWh/m²/yr); all energy, not just HVAC and lighting, and built-up (not carpet) area.
Source: Jul 2022
📖 §10.5 Building envelope — Window-Wall Ratio (WWR)
44. What is window to wall ratio __________
Vertical fenestration area / gross exterior wall area
Vertical fenestration area / Net exterior wall area
gross exterior wall area/ Vertical fenestration area
Net exterior wall area/ Vertical fenestration area
Answer: A) Vertical fenestration area / gross exterior wall area
Confirmed vs Book-3 §10.5 — WWR = vertical fenestration area ÷ gross exterior wall area (gross wall measured horizontally from the exterior surface and vertically from top of floor to bottom of roof). 'Net' wall area and the inverted ratios are wrong.
Source: Jul 2022
📖 §10.3 Energy Conservation Building Code — definition and scope
45. Which of the following statements regarding ECBC are correct?
ECBC defines the norms of energy requirements per cubic metre of area
ECBC does not encourage retrofit of Energy conservation measures
ECBC prescribes energy efficiency standards for design and construction of commercial and industrial buildings
One of the key objectives of ECBC is to minimize life cycle costs (construction and operating energy costs)
Answer: D) One of the key objectives of ECBC is to minimize life cycle costs (construction and operating energy costs)
Confirmed vs Book-3 §10.3 — ECBC sets minimum energy-efficiency standards for design and construction of COMMERCIAL buildings (not industrial, so c is wrong), explicitly encourages energy-efficient design or major RETROFIT (so b is wrong), and its EPI norms are per square metre, not cubic metre (so a is wrong). By elimination (d) — minimising life-cycle (construction + operating energy) cost — is the correct statement.
Source: Mar 2023
Short questions (5 marks) — 13
📖 §10.5 Effective aperture of glazing
1. AI PRACTICE: Define Effective Aperture (EA). For a facade with WWR 0.6 and VLT 0.15, calculate EA and state whether it complies with the ECBC daylighting rule.
Model answer: Effective Aperture (EA) = VLT x WWR; it represents the light-admitting potential of the glazing. EA = 0.15 x 0.6 = 0.09. Since 0.09 is less than the compliance cut-off of 0.1, this facade does NOT comply.
Confirmed vs Book-3 §10.5 (the book's own Case 2, identical figures) — EA = VLT x WWR, with the rule that EA of 0.1 and above complies with ECBC and below 0.1 does not. Here 0.15 x 0.6 = 0.09, which fails; the book's Case 1, WWR 0.4 x VLT 0.26 = 0.104, passes. Write the formula, the product and the explicit pass/fail conclusion. Note that a large window with low-VLT glass can still fail the daylighting check.
Source: AI practice
📖 §10.5 ECBC guidelines on building envelope
2. AI PRACTICE: Define the building envelope and list three of its main functions.
Model answer: The building envelope is the exterior facade of the building, comprising the walls, windows, roof, skylights, doors and other openings. In ECBC terms it is made up of the exterior and semi-exterior elements that separate the conditioned spaces from the weather conditions, or that separate conditioned spaces from unconditioned spaces (e.g. office space from unconditioned storage). Main functions: (1) it protects the building's interior and the occupants from the weather and other external elements; (2) it regulates and optimises heat transfer through roof, walls, windows, skylights, doors and other openings - handling external loads (solar heat gain through windows, heat loss across surfaces, infiltration) and internal loads (lighting, equipment, people) - by effective roof and wall insulation, appropriate glazing and framing, and suitable shading; (3) it admits day light into the interior through windows and skylights, thereby reducing the need for electric lighting, and so strongly affects the visual and thermal comfort of the occupants as well as the building's energy consumption. The envelope must also be sealed, caulked, gasketed or weather-stripped at joints around fenestration and door frames, wall-to-foundation and wall-to-roof openings and service penetrations, to minimise air leakage.
Confirmed vs Book-3 §10.5 — Definition to reproduce verbatim: exterior facade = walls, windows, roof, skylights, doors and other openings, separating conditioned space from the weather or from unconditioned space. Functions cluster into three: weather protection, control of heat transfer (external and internal loads), and daylighting/comfort/energy. Adding envelope sealing earns the extra mark.
3. Match the Following:
1. Solar Heat Gain Coefficient (SHGC)
2. U-value
3. HVAC System Efficiency
4. Cool Roof
5. Thermal Bridging
a. Coefficient of Performance (COP)
b. Solar Reflectance
c. Fenestration Heat Gain
d. Building Insulation
e. Conductive path for unwanted heat transfer
Model answer: Answer Key:
1 → c. Fenestration Heat Gain
2 → d. Building Insulation
3 → a. Coefficient of Performance (COP)
4 → b. Solar Reflectance
5 → e. Conductive path for unwanted heat transfer
Matching per Book-3 §10.5: SHGC → fenestration (solar) heat gain; U-value → insulation/heat flow of the envelope; cool roof → high solar reflectance & emittance; thermal bridging → conductive path of unwanted heat; HVAC efficiency → COP (§10.6).
4. Match the following:
Column A:
1. Envelope Performance Factor (EPF)
2. Luminous Efficacy
3. Economizer
4. Thermal Mass
5. Energy Simulation Software
Column B:
a. Lighting System Efficiency
b. Heat Storage in Building Materials
c. ECBC Compliance
d. Building Energy Performance Modeling
e. Outdoor Air for Free Cooling
Model answer: 1. Envelope Performance Factor (EPF) → c. ECBC Compliance
2. Luminous Efficacy → a. Lighting System Efficiency
3. Economizer → e. Outdoor Air for Free Cooling
4. Thermal Mass → b. Heat Storage in Building Materials
5. Energy Simulation Software → d. Building Energy Performance Modeling
Per Book-3: EPF is the envelope trade-off compliance metric (§10.5); an economizer brings in outside air for free cooling in mild weather (§10.6); energy simulation software models whole-building performance (§10.4); luminous efficacy (lm/W) is lighting efficiency; thermal mass stores heat in building materials.
Source: Sep 2024
📖 §10.10 Building water pumping · §10.15 AHU fan speed · §10.6 Variable-flow hydronic systems (ECBC 5.3.2.3)
5. Name three applications of VFDs in buildings.
Model answer: Three applications of VFDs in buildings (Book-3): (1) Chilled-water and cooling (condenser) water pumps — §10.10 lists 'installation of variable frequency drive for chiller water and cooling water pumps' as a building pumping ECM, and ECBC 5.3.2.3 requires pump motors ≥ 3.7 kW (5 HP) in hydronic systems to be on variable-speed drives so flow is reduced by slowing the motor instead of throttling. (2) Air-handling-unit (AHU) fans — §10.15: install frequency converters to vary AHU fan speed, cutting fan-motor energy by as much as 15%. (3) Cooling-tower fans (Annexure: two-speed or variable-speed drives for cooling-tower fan control) and lift/escalator drive motors (§10.12: type of motor, drive and control system governs energy use). In every case the VFD matches motor speed to actual load, and power falls roughly with the cube of speed.
Book-3 §10.10 (VFD on chilled/cooling water pumps), §10.15 (AHU fan frequency converters, up to 15% saving), §10.6 ECBC 5.3.2.3 (VSD on hydronic pumps ≥ 3.7 kW), Annexure (VSD on cooling-tower fans).
Source: Book EOC
📖 §10.5 Building envelope — Solar Heat Gain Coefficient (SHGC)
6. Explain briefly the meaning of solar heat gain coefficient.
Model answer: The Solar Heat Gain Coefficient (SHGC) is the fraction of incident solar radiation that is admitted through a window or glazing into the building - both the part directly transmitted and the part that is absorbed by the glass and then re-radiated/convected inward. It is a dimensionless number between 0 and 1; a lower SHGC means less solar heat is admitted, which is desirable in hot climates to reduce cooling load, while a higher SHGC admits more solar heat (useful for passive heating in cold climates). ECBC specifies maximum SHGC values for the fenestration of building envelopes.
Book-3 §10.5: SHGC = solar heat gain through fenestration ÷ total incident solar radiation, including directly transmitted and absorbed-then-re-radiated/conducted/convected heat; 0–1, lower = less gain; ECBC Table 10.3 caps SHGC (e.g. 0.25 for WWR ≤ 40% in composite/hot-dry/warm-humid).
7. Match the following Terms in ECBC: 1 Lighting Power Density (LPD); 2 Energy Performance Index (EPI); 3 Effective Aperture (EA); 4 Visible Light Transmittance (VLT); 5 U-Factor — with A Rate of Heat Flow in Watt per m² per °C; B Light admitting potential of a Glazing System; C Watts per square meter; D kWh per square meter per year; E Ratio of light passing through glazing to light through perfectly transmissive glazing.
Model answer: 1-C; 2-D; 3-B; 4-E; 5-A.
Book-3: LPD = W/m² (§10.8); EPI = kWh/m²/year (§10.14); EA = light-admitting potential of a glazing system (§10.5); VLT = ratio of light through glazing to perfectly transmissive glazing; U-factor = heat flow per m² per °C (§10.5).
Source: 17th Sep-2016
📖 §10.15 Energy efficiency measures in buildings · §10.5 envelope/glazing
8. List five energy saving measures in a commercial building.
Model answer: 1) Optimize air conditioning volumes (false ceiling, partition/segregation of critical areas). 2) Reduce solar heat gain through the envelope with efficient glazing. 3) Use energy efficient lighting systems. 4) Use occupancy/motion/sound sensors for lighting. 5) Use energy efficient pumping and air conditioning systems; provide barriers against hot-air leakage; optimize evaporator temperature to ~22°C; avoid heating appliances in cool spaces.
Book-3 §10.15 measures (temperature/humidity settings, efficient lighting, controls, AHU VFDs, weather stripping) plus §10.5 envelope measures (low-SHGC glazing, shading, insulation).
Source: 17th Sep-2016
📖 §10.15 Energy efficiency measures in buildings
9. List four Energy Efficiency measures in buildings. (5 Marks)
Model answer: Four energy-efficiency measures in buildings (Book-3 §10.15): (1) Weather-strip windows and doors (and fit self-closing doors) to minimise exfiltration of conditioned air and infiltration of unconditioned outside air. (2) Set the air-conditioning to 23–25 °C and 55–65% RH, and keep the chilled-water leaving temperature at or above 7 °C — centrifugal chiller efficiency improves about 2.5% per 1 °C rise. (3) Maintain the HVAC plant: keep chilled-water pipe and duct insulation in good condition, mechanically clean condenser tubes at least every six months, keep cooling towers and air filters clean, and install frequency converters on AHU fans (up to 15% fan-energy saving). (4) Efficient lighting: use daylighting with dimming/switch-off controls and separate peripheral switching, replace incandescent lamps with CFL (75% saving), use electronic ballasts (2 W loss vs 12 W) and optical luminaires (up to 50% saving), clean fixtures four times a year and use light-coloured surfaces and task lighting.
Book-3 §10.15 measures: weather stripping; 23–25 °C / 55–65% RH; CHW ≥ 7 °C (2.5%/°C); insulation, condenser cleaning 6-monthly, clean cooling towers and filters, AHU VFD 15%; daylighting/controls, CFL 75%, electronic ballast 2 W vs 12 W, optical luminaires 50%, cleaning 4×/yr, light colours, task lighting.
Source: Mar 2021
📖 §10.15 Energy efficiency measures in buildings
10. List five Energy Efficiency measures in buildings.
Model answer: Five energy-efficiency measures in buildings (Book-3 §10.15): (1) Weather stripping of windows and doors plus self-closing doors to minimise exfiltration of conditioned air and infiltration of outside air. (2) Temperature and humidity setting of 23–25 °C and 55–65% RH; maintain chilled-water leaving temperature at or above 7 °C (centrifugal chiller efficiency rises ~2.5% per 1 °C). (3) Keep chilled-water pipe and duct insulation in good condition; clean chiller condenser tubes at least every six months; keep cooling towers and air filters clean. (4) Install frequency converters (VFDs) to vary AHU fan speed — saves up to 15% of fan-motor energy (also VFDs on chilled/cooling-water pumps, §10.10). (5) Lighting: daylighting with controls that reduce luminaire output by at least half, switch off lights when not in use, separate switches for peripheral lighting, replace incandescent lamps with CFL (75% saving), electronic ballasts (2 W vs 12 W loss), optical luminaires (up to 50%), clean fixtures four times a year, light colours on walls/ceilings and task lighting.
Book-3 §10.15 AC measures (weather stripping, 23–25 °C/55–65% RH, CHW ≥ 7 °C, insulation, condenser cleaning, AHU VFD 15%) and lighting measures (daylighting controls, CFL 75%, electronic ballast, optical luminaires, cleaning, light colours).
Source: Mar 2021 (Set B)
📖 §10.14 EPI · §10.15 AC measures · §10.5 Building envelope & SHGC · §10.8 LPD methods
11. Write short notes on the following (each 2 Marks): a) Energy Performance Index (EPI); b) List any two Energy Efficiency measures in Building air conditioning system; c) Building Envelop from an energy efficiency point of view; d) Difference between building area method and space function method for deriving Lighting Power density (LPD); e) Solar Heat Gain Coefficient (SHGC).
Model answer: a) Energy Performance Index (EPI), §10.14: the specific energy usage of a building = total annual energy consumption (purchased + generated electricity) ÷ built-up area, in kWh/sq m/year; it is the basis of BEE star rating (1–5 Star; label valid 5 years), with EPI bandwidths set per climatic zone and % air-conditioned area — e.g. composite zone, > 50% AC: band 190–90, 5 Star below 90, 1 Star at 165–190 kWh/m²/yr. Built-up area = carpet area + wall thickness + balconies, excluding parking basements. b) Two AC energy-efficiency measures, §10.15: (i) maintain chilled-water leaving temperature at or above 7 °C — centrifugal chiller efficiency improves ~2.5% per 1 °C rise; (ii) install frequency converters to vary AHU fan speed, cutting fan-motor energy by up to 15% (others: weather stripping, 23–25 °C/55–65% RH, 6-monthly condenser cleaning, clean filters). c) Building envelope, §10.5: the exterior façade — walls, windows, roof, skylights, doors and openings — separating conditioned space from the weather/unconditioned spaces. From an energy viewpoint it must handle external loads (solar gain through windows, heat loss/gain across surfaces, infiltration) and internal loads, admit daylight to cut electric lighting, and regulate heat transfer through insulation of roof/walls, proper glazing and framing, shading, cool roofs and sealing/weather stripping of all joints and openings. d) Building Area Method vs Space Function Method, §10.8: both give the interior lighting power allowance = Σ (gross lighted floor area × allowed LPD in W/m²). The Building Area Method applies one LPD by TYPE OF BUILDING to the whole gross lighted area (hotel: 4 × 1000 m² × 10.8 W/m² = 43,200 W); the Space Function Method applies a separate LPD by TYPE OF OPERATION/space and sums the allowances for all spaces (enclosed office 400 m² × 11.8 W/m² = 4,720 W). e) SHGC, §10.5: the ratio of solar heat gain that passes through fenestration to the total incident solar radiation, including directly transmitted and absorbed-then-re-radiated/conducted/convected heat; 0–1, lower means less solar gain (ECBC max e.g. 0.25 for WWR ≤ 40% in hot zones).
Book-3 §10.14 (EPI kWh/m²/yr, star bands), §10.15 (CHW ≥ 7 °C, AHU VFD 15%), §10.5 (envelope definition and design basics; SHGC ratio), §10.8 (building-area vs space-function LPD methods with the two worked examples).
12. Fill in the blanks: (a) ECBC is applicable to commercial buildings having contract demand of ____ kVA. (b) In a centrifugal fan if speed is reduced by 30% static pressure will reduce by ____%. (c) If the speed of a reciprocating pump is reduced by 30%, the power consumption will reduce by ____%. (d) The unit of specific humidity of air is __________. (e) The synchronous speed (rpm) of a 2 pole induction motor at 49 Hz supply frequency is __________.
Model answer: (a) 120 kVA; (b) 51%; (c) 30%; (d) grams moisture/kg of dry air; (e) 2940 rpm
(a) Book-3 §10.2: contract demand 120 kVA (or connected load 100 kW). (b) Static pressure ∝ N²: 1 − 0.7² = 0.51 → 51%. (c) Positive-displacement pump flow and power ∝ speed → 30%. (d) Specific humidity in g (or kg) moisture per kg dry air. (e) Ns = 120 × 49 / 2 = 2940 rpm.
13. Find out the Effective Aperture (EA) of the following two glazing and comment about compliance with ECBC. Case #1: Window to Wall Ratio (WWR) 0.2, Visible Light Transmittance (VLT) Transparent. Case #2: Window to Wall Ratio (WWR) 0.45, Visible Light Transmittance (VLT) 0.2.
Model answer: EA = VLT × WWR. Case #1: EA = 1.0 × 0.2 = 0.2; as EA > 0.1, glazing complies with ECBC. Case #2: EA = 0.2 × 0.45 = 0.09; as EA < 0.1, glazing does not comply with ECBC.
Book-3 §10.5: EA = VLT × WWR; transparent glazing has VLT = 1 so the effective aperture equals the opening. Book examples: 0.4 × 0.26 = 0.104 > 0.1 complies; 0.6 × 0.15 = 0.09 < 0.1 does not comply.
Source: Mar 2023
Long questions (10 marks) — 12
📖 §10.4 Compliance approaches
1. AI PRACTICE: Name the three ECBC compliance approaches and give a one-line description of each.
Model answer: The Code first requires that the building comply with ALL the mandatory provisions; beyond that, three compliance approaches are available. (1) Prescriptive Method - compliance is achieved by meeting or exceeding the specific prescribed level for each individual component (minimum roof/wall insulation R-value, maximum assembly U-factor, fenestration U-factor and SHGC, LPD etc.); simple and quick, but rigid. (2) Envelope Trade-Off Method - allows the designer to trade enhanced efficiency in one envelope component against another (only among roof, walls and fenestration), using the Envelope Performance Factor (EPF) computed as per Appendix D of ECBC; the proposed design's EPF must be equal to or better than that of the baseline design. (3) Whole Building Performance (WBP) Method - uses approved computer energy simulation software as per Appendix B to model the Proposed Design and compare its annual energy consumption with that of the Standard Design; compliance is achieved if the proposed design's energy use is no greater than the standard design's. It gives maximum design flexibility but requires considerable simulation expertise.
Confirmed vs Book-3 §10.4 — Lock the three names and their tools: Prescriptive (component-wise limits), Envelope Trade-Off (EPF, Appendix D, envelope components only), Whole Building Performance (simulation, Appendix B, proposed vs standard design). Open by stating that the mandatory provisions must be met first — it is a mark on its own.
Source: AI practice
📖 §10.14 Star rating (EPI, built-up area) · §10.8 LPD · Ch9 DG set efficiency
2. A Commercial Office building accommodates two government departments. Total employees = 250, of which 70% average present at any time. The building is operational 6 days a week, 10 working Hrs a day. Supply through a 33 kV feeder, stepped down to 415 V. No separate parking, lawn, internal roads. Building information sheet (Annual Data April 24-March 25):
1. Contract Demand (kW): 130
2. Installed capacity DG Set(s) (kVA): 160
3a. Annual Electricity Consumption purchased from Utilities (kWh): 105753
3b. Annual Electricity Consumption through DG Set(s) (kWh): 2136
4a. Annual Cost of Electricity purchased from Utilities (Rs.): 1043557
4b. Annual Cost of Electricity generated through DG Set(s) (Rs.): 54405
5. Built Up Area (sq.m): 3591.96; Conditioned Area (sq.m): 2155.18
6. Installed capacity of Chiller (TR): 137.5
7. Installed lighting load (kW): 8.11
8. Office Appliances (kW): 11.0
9. Other Loads (kW): 12.5
10. HSD Consumption in DG (GCV 10800 Kcal/kg and density 0.85): 585 Litres
Calculate:
a. Total electricity consumed by the building and average electricity unit cost. (2 Mark)
b. EPI of the building for past one year. Recommend the appropriate BEE star rating if the bandwidth of the EPI ranges between 150-50 kWh/sq.m/year. (3 Marks)
c. Design diversity factor of the building, if design EER of the chiller is 3.5 and recorded maximum demand is 75% of the contract demand. (2 Marks)
d. Estimate the overall operating efficiency of the DG set. (2 Marks)
e. Calculate the lighting power density. (1 Mark)
Model answer: a. Total electricity consumed: 105753 + 2136 = 107889 kWh; Average unit cost = (1043557 + 54405) / 107889 = Rs. 10.18 per kWh
b. EPI = 107889 / 3591.96 = 30 kWh/m²/year; the EPI is below the bandwidth for star rating, hence 5 Star rated.
c. Diversity Factor = Maximum Demand / Connected Load; Maximum Demand = 130 × 0.75 = 97.5 kW; Connected Load = Lighting + appliances + others + AC = 8.11 + 11.0 + 12.5 + (137.5 × 3024/860/3.5) = 169.75 kW; Diversity Factor = 97.5/169.75 = 0.57 (or 169.75/97.5 = 1.74)
d. Overall DG Set efficiency = (2136 × 860) / (585 × 0.85 × 10800) = 34.2%
e. Lighting Power Density = 8.11 × 1000 / 3591.96 = 2.25 W/m²
EPI = annual energy ÷ built-up area (§10.14); DG η = kWh × 860 ÷ (litres × density × GCV); diversity factor = max demand ÷ connected load; LPD = installed lighting W ÷ area (§10.8). Chiller kW = TR × 3024 ÷ 860 ÷ EER.
3. L3 a) Match the following: (4 Marks)
1 Prescriptive Approach
2 Whole Building Performance Approach
3 Building envelope
4 Effective Aperture
Options:
1. Exterior façade
2. Trade-Off option
3. light admitting potential
4. Uses simulation to show compliance for the entire building
b. Fill in the following blank statements:
1. The Effective Aperture (EA) or light admitting potential of a glazing system is determined by multiplying the Visible Light Transmittance (VLT) of the glazing by the _____ of the building.
2. Thermal emittance is the relative ability of a material to _____ the absorbed heat.
3. If a window has a SHGC of 0.25 and the total incident solar radiation is 600 W/m², the solar heat gain through the window is _____
4. The emissivity of a material is the ratio of energy radiated by a particular material to energy radiated by a _____ at the same temperature.
5. As per ECBC the unit of Energy Performance Index (EPI) _____
6. Fenestration surface having a slope of less than 60 degrees from the horizontal plane is termed _____ (6 Marks)
Model answer: a) 1. Prescriptive Approach – b (Trade-Off option)
2. Whole Building Performance Approach – d (Uses simulation to show compliance for the entire building)
3. Building envelope – a (Exterior façade)
4. Effective Aperture – c (light admitting potential)
b) 1. ... multiplying the VLT of the glazing by the Window-Wall Ratio (WWR) of the building.
2. Thermal emittance is the relative ability of a material to radiate the absorbed heat.
3. Solar heat gain through the window = 0.25 × 600 = 150 W/m².
4. ... energy radiated by a black body at the same temperature.
5. As per ECBC the unit of EPI = kWh/Sq.mt/year.
6. Fenestration surface having a slope of less than 60 degrees from the horizontal plane is termed Skylight.
Book-3: Prescriptive method offers the envelope Trade-Off option; WBP uses simulation (§10.4); envelope = exterior façade; EA = VLT × WWR; thermal emittance = ability to radiate absorbed heat, emissivity relative to a black body; SHGC × incident radiation = 0.25 × 600 = 150 W/m²; EPI in kWh/sq m/year (§10.14); skylight = fenestration sloped < 60° from horizontal (§10.5).
Source: Sep 2024
📖 §10.5 ECBC guidelines on building envelope — definition, sealing and design basics
4. What do you understand by building envelope? What are its functions?
Model answer: Building envelope (Book-3 §10.5): the exterior façade of a building, comprising the walls, windows, roof, skylights, doors and other openings. It includes the exterior and semi-exterior elements that separate the conditioned spaces from the weather, or the conditioned spaces from unconditioned spaces (e.g. office from unconditioned storage). Functions: (1) protects the building's interior and occupants from weather conditions and other external elements; (2) controls heat transfer through roof, walls, windows, skylights and doors — regulating external loads (solar heat gain through windows, heat loss/gain across envelope surfaces, infiltration) so that internal cooling/heating loads are minimised, via insulation of roof and walls, suitable glazing/framing and shading; (3) admits daylight through windows and skylights (proper orientation, size and placement) to reduce electric lighting; (4) minimises air leakage — joints, penetrations and openings are sealed, caulked, gasketed or weather-stripped; (5) strongly affects the visual and thermal comfort of occupants and hence the building's energy consumption. ECBC prescribes maximum U-factors/minimum R-values for walls and roofs, maximum U-factor and SHGC for fenestration, cool-roof reflectance ≥ 0.7 and emittance ≥ 0.75, and skylight area ≤ 5% of roof.
Book-3 §10.5: envelope = exterior façade (walls, windows, roof, skylights, doors, openings) separating conditioned from unconditioned/outdoor; functions — weather protection, heat-transfer control (insulation, glazing, shading), daylighting, air-leakage sealing, comfort and energy use.
Source: Book EOC
📖 §10.5 Building envelope — U-Factor (W/m²K) and Tables 10.1–10.3
5. What is the significance of the overall heat transfer coefficient (U-factor) in building energy consumption?
Model answer: U-factor (overall heat transfer coefficient), Book-3 §10.5: when there is a temperature difference between inside and outside, heat is lost or gained through walls, roof, window frame and glazing by the combined effects of conduction, convection and long-wave radiation. The U-factor is the rate of heat flow through one square metre of wall/roof/fenestration assembly for a 1 °C temperature difference (W/m²·°C or W/m²·K); it is the reciprocal of the assembly's thermal resistance (R-value). Significance: the lower the U-factor, the less heat transfer takes place — so less heat enters in summer (lower cooling load in hot climates) and less escapes in winter (lower heating load in cold climates), directly reducing HVAC energy consumption. Centre-of-glass U-factors are lower than whole-window U-factors, which include the frame and mullions. ECBC therefore prescribes climate-wise maximum U-factors (or minimum insulation R-values): opaque walls max 0.440 W/m²°C (R-2.10) in composite/hot-dry/warm-humid zones; roofs 0.261 (R-3.5) for 24-hour buildings and 0.409 (R-2.1) for daytime buildings; vertical fenestration max 3.30 W/m²°C (6.90 in the moderate zone). Selecting low-U (well-insulated) envelope components is thus a primary way to cut building energy use.
Book-3 §10.5: U-factor = heat flow per m² per 1 °C (W/m²K), lower = less transfer = lower heating/cooling load; whole-window > centre-of-glass; ECBC Tables 10.1–10.3 set maximum U-factors by climate zone.
Source: Book EOC
📖 §10.13 Building Energy Management System (BEMS/BMS)
6. Explain the term Building Management System (BMS).
Model answer: Building Management System (BMS) / Building Energy Management System (BEMS), Book-3 §10.13: energy management systems range from the simplest timer that switches systems ON/OFF at pre-determined intervals, through programmers, thermostatic controls, motorised valves, zoning, optimum-start controllers and compensated circuits, up to the most complex systems with a computerised central controller linked to numerous sensors and information sources — internal and external air temperature, humidity, atmospheric pressure, plus processed data such as time, day of week, time of year, percentage occupancy, meteorological data, plant-efficiency feedback and energy gains from sun, lighting, machinery and people. A microprocessor is the main feature: data on temperature, flow rates and pressures are collected from sensors and stored; equations describing the performance of control elements, plant and systems are fed in as algorithms, so deviations from the desired performance are handled by calculation and plant output varied accordingly (mathematical functions replace control modes — e.g. computing the correct hot-water valve position to return a room to set point without offset). Trends can be stored, anticipation built in to prevent excessive swings, and self-correction allows the system to learn from experience. The functions of a BMS/BEMS are the monitoring and control of the services and functions of a building in a way that is economical and efficient in the use of energy; one system can control a group of buildings. Optimum results require properly designed, installed and commissioned systems.
Book-3 §10.13: BMS/BEMS = computerised central controller + sensors + microprocessor algorithms that monitor and control building services (HVAC, lighting, plant) economically and energy-efficiently; can control a group of buildings.
Source: Book EOC
📖 §10.15 Energy efficiency measures in buildings (AC & lighting) · §10.10 pumping · §10.6 HVAC
7. List ten energy conservation measures in buildings.
Model answer: Ten energy conservation measures in buildings (Book-3 §10.15, §10.10, §10.6): (1) Weather-strip windows and doors and provide self-closing doors to minimise exfiltration of conditioned air and infiltration of outside air. (2) Set space temperature at 23–25 °C and relative humidity at 55–65%. (3) Maintain chilled-water leaving temperature at or above 7 °C — centrifugal chiller efficiency rises about 2.5% per 1 °C rise. (4) Keep insulation of chilled-water pipes and air ducts in good condition to prevent heat gain. (5) Mechanically clean chiller condenser tubes at least every six months and keep cooling towers clean; use soft water to prevent scaling. (6) Install frequency converters (VFDs) on AHU fans (saves up to 15%) and on chilled/cooling-water pumps; keep air filters clean. (7) Use daylighting with controls that dim or switch off luminaires (ECBC: reduce output by at least half in daylit areas), separate switching for peripheral lighting, and switch off lights when not in use. (8) Replace incandescent and inefficient lamps with high-efficacy lamps (CFL saves 75%) and conventional ballasts (12 W loss) with electronic ballasts (2 W loss); use optical luminaires (up to 50% saving) and clean fixtures at least four times a year. (9) Integrate lighting with air-conditioning (extract return air through luminaires), use light colours on walls/ceilings, task lighting and eliminate excessive lighting. (10) Improve the envelope — insulation, cool roof, low-SHGC glazing and shading — and install a BMS/BEMS with high-efficiency pumps, parallel operation and auto level control for water pumping.
Book-3 §10.15 AC measures (weather stripping, 23–25 °C/55–65% RH, CHW ≥ 7 °C, insulation, condenser cleaning 6-monthly, AHU VFD 15%, clean filters) and lighting measures (daylighting controls, switch-off, CFL 75%, electronic ballast 2 W vs 12 W, optical luminaires 50%, integration with AC, cleaning 4×/yr, light colours, task lighting); §10.10 pumping ECMs; §10.5 envelope.
Source: Book EOC
📖 §10.5 Building envelope — solar reflectance, fenestration, VLT, effective aperture
8. Explain the following terms: a) solar reflectance, b) fenestration, c) visible light transmittance, d) effective aperture of glazing.
Model answer: (a) Solar reflectance (Book-3 §10.5): the fraction of solar radiation reflected by a roof/surface, measured across the solar spectrum on a scale of 0 (perfect absorber) to 1 (perfect reflector); its complement is absorptance (Reflectance + Absorptance = 1). Cool roofs need reflectance ≥ 0.7 (with emittance ≥ 0.75). (b) Fenestration: windows, skylights, ventilators and doors that are more than one-half glazed — all openings (including frames) in the building envelope that let in light. A skylight is a fenestration surface sloped less than 60° from horizontal; all other fenestration is vertical fenestration. (c) Visible Light Transmittance (VLT): the ratio of light passing through the glazing to light passing through perfectly transmissive glazing; it concerns only the visible part of the solar spectrum (unlike SHGC, which covers all solar radiation) and is the key parameter for daylighting. (d) Effective Aperture (EA) of glazing: the light-admitting potential of a glazing system = VLT × Window-Wall Ratio (WWR, vertical fenestration area ÷ gross exterior wall area). Aperture size alone does not determine daylight because the glazing reduces transmitted light — VLT 0.5 halves the effective opening. Book example: WWR 0.4 × VLT 0.26 = 0.104 (> 0.1, complies with ECBC); WWR 0.6 × VLT 0.15 = 0.09 (< 0.1, does not comply).
Book-3 §10.5: reflectance 0–1, reflectance + absorptance = 1; fenestration = windows/skylights/ventilators/≥half-glazed doors; VLT = visible light ratio vs perfectly transmissive glazing; EA = VLT × WWR with ECBC threshold 0.1.
Source: Book EOC
📖 §10.15 Energy efficiency measures in buildings (plus Ch3 compressed air, Ch6 pumps, Ch8 lighting)
9. List five energy conservation measures each for any two of: a) Energy use in buildings, b) Compressed air system, c) Pumps and pumping systems, d) Lighting systems.
Model answer: Buildings: weather-stripping of windows/doors; set temperature 23-25°C and RH 55-65%; maintain chilled water leaving temp ≥7°C; insulate chilled water pipes and ducts; clean condenser tubes every 6 months; keep cooling towers clean; vary AHU fan speed with VFD; keep air filters clean. Compressed air: keep intake air cool (every 4°C rise raises power 1%); clean inlet filters (2% loss per 250 mmWC drop); ring-main piping; carry out leak tests (40-50% leakage common); fit solenoid cut-off valves; reduce delivery pressure; use VFD on large compressors; separate HP/LP systems. Pumps: ensure adequate NPSH; operate near BEP; minimize throttling; use VSD for load variation; trim/replace oversized impellers; replace with energy-efficient pumps; reduce system resistance by pipe sizing. Lighting: switch off lights when not in use; separate switching for peripheral/daylit zones; use high-efficacy lamps (CFL saves ~75%); electronic ballasts (2 W vs 12 W); optical luminaires; clean fixtures; light-coloured surfaces; lighting controls (timers, daylight, occupancy sensors).
Buildings list is Book-3 §10.15 verbatim (weather stripping, 23–25 °C/55–65% RH, CHW ≥ 7 °C, insulation, condenser cleaning every 6 months, clean cooling towers, AHU VFD, clean filters); other systems from their own chapters.
Source: 15th Exam
📖 §10.5 Building envelope — SHGC, VLT, Cool roof
10. Write short notes on any two of the following: (1) Solar Heat Gain Coefficient (SHGC), (2) Visible Light Transmittance (VLT), (3) Cool Roof. (Each 2.5 Marks)
Model answer: (1) SHGC: Fraction of incident solar radiation admitted through a window (both directly transmitted and absorbed-then-reradiated inward); ranges 0-1, lower SHGC means less solar heat gain - ECBC specifies maximum SHGC for fenestration. (2) VLT: Visible Light Transmittance - the fraction of visible light (380-780 nm) transmitted through glazing; higher VLT gives more daylight. ECBC encourages high VLT with low SHGC for daylighting without heat gain. (3) Cool Roof: A roof surface with high solar reflectance and high thermal emittance that stays cooler under the sun, reducing roof heat gain, cooling load and the urban heat island effect.
Book-3 §10.5: SHGC = solar heat gain through fenestration ÷ incident solar radiation (transmitted + absorbed/re-radiated); VLT = visible light ratio vs perfectly transmissive glazing (daylighting); cool roof = high solar reflectance (≥ 0.7) and high emittance (≥ 0.75) to reflect and reject heat.
Source: Sep 2019
📖 §10.4 Compliance approaches (Prescriptive vs Whole Building Performance) · §10.5 envelope terms
11. L-2(A): Classify each as Prescriptive Method or Whole Building Performance Method: (1) Compliance by meeting/exceeding specific levels for each individual element; (2) Allows trade-off option for building envelope; (3) Allows use of energy simulation software; (4) Computer model of proposed design compared with Standard Design; (5) Compliance if proposed design energy use is less than standard design. (B) Match building-envelope terms.
Model answer: A. (1) Prescriptive Method; (2) Prescriptive Method; (3) Whole Building Performance Method; (4) Whole Building Performance Method; (5) Whole Building Performance Method. B. (1) Building envelope - (c) Roof, walls, windows, skylights, doors and other openings; (2) Passive solar design strategy - (e) Cross ventilation; (3) Visual Light Transmittance - (a) Day lighting of building; (4) Weather stripping - (b) Exfiltration and Infiltration of air; (5) Cool roof - (d) Property of high solar reflectance and emittance.
Book-3 §10.4: Prescriptive = meet/exceed specified levels for each element and includes the envelope Trade-Off option; WBP = simulation software, computer model of Proposed Design vs Standard Design, complies if proposed energy use is not greater. Part B terms from §10.5 (envelope, cross-ventilation, VLT/daylighting, weather stripping, cool roof).
Source: Sep 2019
📖 §10.15 Energy efficiency measures · §10.13 BEMS · §10.3 ECBC scope & climatic zones
12. L-5: Write short notes on any two of the following: (a) Energy Efficiency Measures in Buildings; (b) Building Management System (BMS); (c) Energy Conservation Building Codes (ECBC).
Model answer: (a) Energy Efficiency Measures in Buildings - Air-Conditioning System: weather stripping of windows/doors (minimise infiltration; self-closing doors); temperature 23-25 C and RH 55-65%; maintain chilled water leaving temperature at or above 7 C (centrifugal chiller efficiency rises ~2.25% per 1 C rise in leaving temp); maintain insulation of chilled water pipes and ducts; clean chiller condenser tubes at least every six months; keep cooling towers clean; install frequency converters for AHU fan speed (saves up to 15%); keep air filters clean. Lighting System: switch off lights when not in use; separate switches for peripheral lighting (use daylight); install high-efficiency lighting (CFL for incandescent saves 75%); use electronic ballasts (losses 2W vs 12W conventional); optical luminaires (aluminium/silver/dielectric) save up to 50%; integrate lighting with AC (return air through luminaires); clean lights/fixtures (dust 4 times a year); use light colours for walls, floors, ceilings. (b) Building Management System (BMS) - Energy management systems range from simple ON/OFF timers up to a computerised central controller linked to numerous sensors (temperature, flow, pressure) and data sources (time, day, occupancy, meteorology, solar/internal gains). A microprocessor stores sensor data; performance equations (algorithms) compute deviations from desired conditions and control plant (e.g., adjusting chilled-water valve to AHU to hold set point). Trends can be stored, anticipation and self-correction built in. The function of a BMS/BEMS is economical and efficient monitoring and control of building services; one system can control a group of buildings. (c) Energy Conservation Building Codes (ECBC) - set minimum energy efficiency standards for design/construction of commercial and residential buildings without constraining function, comfort, health or productivity. India is grouped into five climatic zones: Composite (Delhi), Hot-Dry (Ahmedabad), Warm-Humid (Kolkata), Moderate/Temperate (Bangalore), Cold (Shillong). ECBC covers: building envelopes (except unconditioned storage/warehouses), mechanical systems and equipment (HVAC), service hot water heating, interior and exterior lighting, and electrical power and motors. It does not apply to buildings using neither electricity nor fossil fuel, equipment/systems using energy primarily for manufacturing processes, and multi-family buildings of three or fewer storeys plus single-family buildings.
Book-3 §10.15 (AC and lighting measures with the book's figures), §10.13 (BEMS: computerised central controller, sensors, microprocessor algorithms, self-correction, one system for a group of buildings), §10.3 (ECBC = minimum energy-efficiency standards for commercial buildings; five zones; covers envelope, HVAC, service hot water, lighting, electrical power & motors; excludes buildings using neither electricity nor fossil fuel and manufacturing-process equipment).