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Space load verification against CIBSE Guide A 2015 and ASHRAE Fundamentals 2021

The office module that Guide A works through in Appendix 5.A6, and the Atlanta office of the ASHRAE Handbook's Chapter 18 example, run through the same calculations the app uses, line by line against the printed figures: the steady-state heat loss, the cyclic-model cooling load at its peak hour, the sol-air temperature, and the conduction and radiant time series.

Result
14 of 14 checks pass
Cases
5 worked examples
Version / published
v1.0 · 2026-09-25
Engine fingerprint
33b989b26d4c

Why we publish this

Guide A and the ASHRAE Handbook are the references this calculation cites. Both print worked examples with every input and every intermediate, so a calculation can be checked against the method rather than against its own code. Each case above names the standard, the example and the printed page; a figure worked from printed inputs has to land within 2 %.

The cooling examples fix their weather from the standards' own tables (Guide A Tables 2.13, 2.14 and 5.16; ASHRAE Table 27 and the Chapter 14 clear-sky model), where the calculator normally builds its design day from the weather station. For these cases the printed series are handed to the calculation as inputs, and everything from there on, the cyclic conduction with the printed decrement and lag, the tabulated solar cooling load, the internal gains, the infiltration and the sum at the peak hour, is the calculation as it runs for any room.

What is not compared, and why

  • Example 5.A6.2, the peak summertime temperature. The calculation reports loads; it does not predict the free-running operative temperature of an uncooled room.
  • Example 5.A6.3's fabric and internal gains taken separately. The print reduces both to the air node with the room-conductance factors Fcu = 0.99 and Fcy = 0.86 (its equations 5.55 and 5.56); the calculation carries them unreduced, which is the 1.8 % by which its total sits above the print. The total, the tabulated solar gain and the infiltration are compared.
  • Example 5.A6.1's fabric loss as the text prints it (644.8 W). The print's own Table 5.A6.3 sums the conductances to 28.43 W/K, which gives 625.5 W at 22 K, while its text and Table 5.A6.4 carry 29.31 W/K. The table's arithmetic is compared, and the printed total of 1222.3 W is met within the 2 % policy.
  • ASHRAE Chapter 18 Parts 3 to 5, the window and the room total. The print's window takes a beam solar heat gain coefficient and an indoor attenuation coefficient that change with the sun's angle hour by hour, and its room total needs separate schedules for lights, people and equipment and a return-air plenum share. The calculation models none of these, so there is nothing like-for-like to compare; the lighting and the wall, whose method it does share, are compared instead.

How to read the tables

  • Expected is the value printed in the standard, or a hand calculation from printed values. The working is shown under each quantity.
  • Tolerance is exact for tabulated values and selected sizes, and ±2 % for calculated quantities such as fabric, infiltration and ventilation losses, the peak-hour cooling load, the sol-air temperature and the time-series loads.
  • Every check re-runs automatically whenever the calculation code changes, and this page is regenerated from those results. The engine fingerprint above identifies the calculation code the results came from.

Sources

  • ASHRAE Handbook—Fundamentals 2021 (SI)
  • CIBSE Guide A 2015, Environmental design

Printed page numbers refer to the editions above.

Worked examples

SL-01

Guide A Example 5.A6.1 — steady-state heat loss of the office module, occupied with natural ventilation

Inputs

  • Office 4.5 × 4.5 × 3.0 m (60.75 m³), intermediate floor, operative temperature 21 °C
  • External design temperature −1 °C, normal exposure
  • South wall 8.6 m² at U 0.35; west wall 8.1 m² at U 0.35 W/m²·K
  • South glazing 4.86 m² at U 2.2; west glazing 5.4 m² at U 2.2 W/m²·K
  • Infiltration 0.111 h⁻¹ (air permeability 5 m³/m²·h); two occupants at 10 L/s each

The print's Table 5.A6.3 sums the fabric conductances to 28.43 W/K while its text and Table 5.A6.4 carry 29.31 W/K; the calculation reproduces the table's arithmetic, and the printed total is met within the ±2 % policy.

Checks for case SL-01
QuantityExpectedSourceMEPCalcΔToleranceResult
Fabric heat loss
Table 5.A6.3 Σ(A × U) = 3.02 + 2.84 + 10.69 + 11.88 = 28.43 W/K; × (21 − (−1)) K = 625.5 W
625.5W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Table 5.A6.3 (conductances) and Table 5.A6.4 (summary) (held copy pp.579 to 581)
625W0.08 %±2 %Pass
Infiltration heat loss
Cv = 0.111 × 60.75 / 3 = 2.25 W/K; × 22 K = 49.5 W
49.5W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Table 5.A6.3 (conductances) and Table 5.A6.4 (summary) (held copy pp.579 to 581)
50W1.01 %±2 %Pass
Ventilation heat loss
20 L/s = 1.185 h⁻¹; Cv = 1.185 × 60.75 / 3 = 24.00 W/K; × 22 K = 528.0 W
528W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Table 5.A6.3 (conductances) and Table 5.A6.4 (summary) (held copy pp.579 to 581)
531W0.57 %±2 %Pass
Total design heat loss
Table 5.A6.4 case (a): (29.31 + 26.25) × 22 = 1222.3 W (the print's text uses 29.31 W/K for the fabric)
1222.3W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Table 5.A6.3 (conductances) and Table 5.A6.4 (summary) (held copy pp.579 to 581)
1206W1.33 %±2 %Pass

SL-02

Guide A Example 5.A6.3 — sensible cooling load of the office module at 15:30 in September, Manchester

Inputs

  • Same module, slow thermal response, control temperature 24 °C, infiltration 0.1 h⁻¹
  • South wall f = 0.99, φ = 1 h; west wall f = 0.30, φ = 9 h (Table 5.A6.7)
  • Mean sol-air 23.1 °C south and 20.4 °C west; 40.3 °C at 14:30 (south), 14.2 °C at 06:30 (west) (Table 2.14(h))
  • Mean outside air 17.1 °C; 22.7 °C at 15:00 (Table 2.14(h))
  • Table 5.16(h) cooling loads at 15:30 September: 451 W/m² south, 385 W/m² west; shading factor 0.6
  • Two occupants at 80 W sensible, IT equipment 10 W/m², 09:00 to 17:00; lighting off

The weather comes in as the print gives it, through the engine's printed-weather override: the daily-mean and lagged-hour sol-air temperatures, the outside air temperature at the peak hour and the Table 5.16 solar cooling loads. The print reduces its fabric and internal gains to the air node with Fcu = 0.99 and Fcy = 0.86; the calculation carries them unreduced, which is the 1.8 % difference on the total.

Checks for case SL-02
QuantityExpectedSourceMEPCalcΔToleranceResult
Solar cooling load through the glazing
0.6 × 4.86 × 451 + 0.6 × 5.4 × 385 = 1315.12 + 1247.40 W
2562.52W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Example 5.A6.3 (held copy pp.586 to 592)
2562.54W0.00 %±2 %Pass
Infiltration gain at the peak hour
Cv = 0.1 × 60.75 / 3 = 2.025 W/K; × (22.7 − 24) K
-2.63W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Example 5.A6.3 (held copy pp.586 to 592)
-2.6W1.14 %±2 %Pass
Sensible cooling load at the peak hour
−47.05 + 362.85 + 2562.52 − 2.63 W (eq. 5.54, control on operative temperature)
2875.69W
CIBSE Guide A 2015, Environmental design
Appendix 5.A6, Example 5.A6.3 (held copy pp.586 to 592)
2928.1W1.82 %±2 %Pass

SL-03

ASHRAE Ch.18 Part 6 — room heating load of the single-room example, Atlanta

Inputs

  • Windows 7.44 m² at U 3.18; spandrel wall 11.14 m² at U 0.44; brick wall 9.29 m² at U 0.45; roof 12.08 m² at U 0.18 W/m²·K
  • Indoor 22.2 °C, 99.6 % heating design dry-bulb −5.6 °C
  • Infiltration one air change per hour on 33.2 m³ (9.2 L/s)
Checks for case SL-03
QuantityExpectedSourceMEPCalcΔToleranceResult
Fabric heat loss
658 + 136 + 116 + 60 W (windows, spandrel, brick, roof as printed)
970W
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.2 Part 6, printed p18.54
971W0.10 %±2 %Pass
Infiltration heat loss
9.2 × 1.23 × (22.2 − (−5.6)) W
315W
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.2 Part 6, printed p18.54
315W0.00 %±2 %Pass
Total design heat loss
1285W
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.2 Part 6, printed p18.54
1286W0.08 %±2 %Pass

SL-04

ASHRAE Ch.18 Part 1 — lighting cooling load at 15:00 by the radiant time series

Inputs

  • One pendant fluorescent luminaire, 110 W, on from 07:00 to 19:00
  • Table 3: 57 % radiant, 43 % convective
  • Table 19 nonsolar RTS, medium-weight construction, 50 % glass, carpeted floor
Checks for case SL-04
QuantityExpectedSourceMEPCalcΔToleranceResult
Lighting cooling load at 15:00
Convective 110 × 0.43 = 47.3 W plus the radiant series through Table 19, 55.7 W
103W
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.1 Part 1, printed p18.47
103.103W0.10 %±2 %Pass

SL-05

ASHRAE Ch.18 Part 2 — spandrel wall facing 60° west of south at 15:00 in July

Inputs

  • Wall 5.57 m² at U 0.44 W/m²·K, dark surface (α/hₒ = 0.053), indoor 23.9 °C
  • Outdoor 33.3 °C and total surface irradiance 617 W/m² at 15:00 (Chapter 14 clear-sky model)
  • Table 29B sol-air temperatures for the 24 hours; Table 16 wall 1 conduction time series
  • Table 14: 46 % radiant; Table 19 nonsolar RTS, medium-weight construction

The text's own convolution (p18.49) prints 83.5 W and 72 W from an earlier heat-input list; Table 29B, computed from the sol-air column it prints, gives 81 W and 71 W, and that is what is compared.

Checks for case SL-05
QuantityExpectedSourceMEPCalcΔToleranceResult
Sol-air temperature at 15:00
33.3 + 0.053 × 617 − 0 °C (eq. 29)
66°C
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.1 Part 2 and Table 29B, printed pp18.48 to 18.50
66°C0.00 %±2 %Pass
Wall heat gain at 15:00 (conduction time series)
Table 29B, hour 15, heat gain column (eq. 31 over the 24-h heat input)
81W
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.1 Part 2 and Table 29B, printed pp18.48 to 18.50
81.8212W1.01 %±2 %Pass
Wall cooling load at 15:00 (radiant time series)
Table 29B, hour 15, total cooling load column (54 % convective plus the radiant series)
71W
ASHRAE Handbook—Fundamentals 2021 (SI)
Chapter 18 §9.1 Part 2 and Table 29B, printed pp18.48 to 18.50
71.0813W0.12 %±2 %Pass