Cooling Load Calculator – Accurate HVAC Sizing & Cost

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Cooling Load Calculator – Theme-Isolated with Expanded Presets (Patched)

Cooling Load Calculator — What it is, how it works, and a full worked example

This interactive tool estimates **sensible & latent cooling loads** for one or more rooms, helps you pick a system size (in kW/TR), and even estimates **airflow and costs**. It supports SI/Imperial units, standards-based presets (ASHRAE / ISHRAE / CIBSE), and generates a clean printable report.

Multi-room (segments)
SI / Imperial Toggle
Cost & Energy
Report Builder

What this calculator does

It estimates each segment’s **sensible heat** (dry temperature rise), **latent heat** (moisture removal), and **total load**. You can add multiple rooms, apply a preset (e.g., Classroom, Gym, Restaurant), and switch standards to auto-fill typical **U-values, set points, and ventilation starters**. The tool then converts the total load into **kW** and **tons of refrigeration (TR)**, estimates **airflow** (~400 CFM/TR), and—if you want—calculates **equipment & energy costs** for India, US, or UK.

When you choose a standard, the widget shows: “Values derived from <Standard>, clause <xx> (user must verify).”

How it works (in plain English)

Inside the math

  • Envelope sensible: Q = U · A · ΔT for walls, roof, windows.
  • Solar gains: Window area × Solar factor × SHGC/SC.
  • Internals: People sensible/latent, lighting = LPD × area, equipment split by sensible fraction.
  • Ventilation & infiltration sensible: Q = ρ · cp · V̇ · ΔT (ρ≈1.2 kg/m³, cp≈1.005 kJ/kg·K).
  • Ventilation latent: From humidity ratio difference Wout − Win, using a Magnus–Tetens saturation approximation and hfg≈2,501 kJ/kg.
  • Total load: Qtot = QS + QL; SHR = QS/Qtot.

Want a refresher on moist air and humidity ratio? See Psychrometrics: Moist Air Made Easy.

Units & outputs

  • Toggle **SI/Imperial** anytime—values convert on the fly.
  • Capacity in **kW** and **TR** (1 TR ≈ 3.517 kW ≈ 12,000 BTU/h).
  • Airflow estimate (rule-of-thumb) ≈ 400 CFM/TR (≈0.188 m³/s per TR).
  • Electrical input from **COP/EER**; energy cost from **tariff**.

For duct sizing and pressure topics, check Ductwork via Bernoulli or our ASHRAE-based Duct Design Calculator.

Show formulas & symbols

Envelope: Q_{wall} = U_{wall}A_{wall}ΔT, Q_{roof} = U_{roof}A_{roof}ΔT, Q_{win} = U_{win}A_{win}ΔT

Solar: Q_{solar} = (Solar\,factor)\,A_{win}\,SHGC

People: Q_{p,S} = N · q_{S,pp}, Q_{p,L} = N · q_{L,pp}

Lighting: Q_{light} = LPD · A; Equipment: split by sensible fraction SF

Vent (sensible): Q_{vs} = ρ c_p V̇ ΔT; Vent (latent): Q_{vl} = h_{fg} ṁ_{dry}(W_{out}-W_{in})

How to use the calculator

  1. Choose unit system (SI or Imperial).
  2. Select a standard (ASHRAE / ISHRAE / CIBSE) to prefill typical U-values and set points. A note appears: “Values derived from <Standard>, clause <xx> (user must verify).”
  3. Add segments for each room/zone. Give each a name (e.g., “Office 1”).
  4. Apply a preset (Office, Classroom, Restaurant, etc.) or enter your own areas, U-values, internal gains, and air quantities.
  5. Optional costing: pick country (India / US / UK), set equipment rate per TR, electricity tariff, markup, hours/day, and days/month.
  6. Press Calculate to update KPIs, table, chart, and cost summary.
  7. Reverse mode lets you start with a target TR and estimate allowable floor area.
  8. Click Generate Report to get a printable HTML report with KPIs, tables, assumptions, and metadata.

Need background on heat-transfer ideas? Try Basics of Heat Transfer and Thermal Conduction.

Sample project — Two-room office suite (full calculation)

Standard: ASHRAE defaults; Units: SI; Country: India (editable). Indoor 24 °C, 50 % RH; Outdoor 35 °C, 60 % RH.

Segment A — Office (20 m²)

  • Geometry: area 20 m², height 3.0 m; exposed wall 30 m²; roof 20 m²; window 4 m².
  • Envelope: Uwall=0.6, Uroof=0.3, Uwin=2.8; Solar factor=200 W/m²; SHGC=0.5.
  • Internals: people=4 → 75/55 W per person; LPD=10 W/m²; equipment=600 W (SF=0.9).
  • Air: infiltration=0.8 ACH; ventilation=8 L/s·person.

Step-by-step (kW)

ItemLoad (kW)
Wall conduction (U·A·ΔT)0.198
Roof conduction0.066
Window conduction0.123
Solar through glazing0.400
People sensible0.300
Lighting (LPD·A)0.200
Equipment sensible0.540
Vent/Inf. sensible (ρ·cp·V̇·ΔT)0.601
Sensible subtotal2.429
People latent0.220
Equipment latent0.060
Vent latent (hfg·ṁ·ΔW)1.650
Latent subtotal1.930
Total (kW)4.358
Total (TR)1.24
SHR0.557

Segment B — Meeting room (30 m²)

  • Wall 40 m²; roof 30 m²; window 6 m²; solar factor 220 W/m²; SHGC 0.5.
  • People 8 (75/55 W pp); LPD 12 W/m²; equipment 800 W (SF 0.9).
  • ACH 1.0; ventilation 8 L/s·person.
ItemLoad (kW)
Sensible subtotal4.068
Latent subtotal3.759
Total (kW)7.827
Total (TR)2.23
SHR0.520

Grand totals

Grand Sensible
6.50 kW
S = 2.429 + 4.068
Grand Latent
5.69 kW
L = 1.930 + 3.759
Total Capacity
12.19 kW
≈ 3.46 TR
SHR
0.533
S / (S + L)
Airflow (est.)
≈ 1,386 CFM
~0.651 m³/s

Electrical & cost (Country = India)

With COP = 3.5 (≈ EER 11.9), electricity tariff ₹6.47/kWh, hours/day 8, days/month 26:

Electrical Input
3.48 kW
= 12.19 / 3.5
Energy Cost / hr
₹22.53
3.48 × 6.47
Energy Cost / month
₹4,685
₹22.53 × 8 × 26
Equipment (est.)
₹100,049
₹25k/TR × 3.46 TR × (wastage 5% + markup 10%)

Quick comparison — US & UK (same load, same COP)

US Equipment
$5,203
$1,300/TR, +5% waste, +10% markup
US Energy / hr
$0.61
$0.1747/kWh
US Energy / month
$126.51
8h × 26d
UK Equipment
£10,005
£2,500/TR, +5% waste, +10% markup
UK Energy / hr
£0.90
£0.2573/kWh
UK Energy / month
£186.33
8h × 26d

Prices & tariffs are editable placeholders—update to match your market. For envelope/airflow decisions after you size equipment, see Duct Design Calculator (ASHRAE) and Pipe Design: Head Loss & Fittings.

Pro tips to get reliable results

  • Use presets first, then tweak. They’re area-aware (m²/person) and bring you close to typical internal gains.
  • Double-check ventilation. Ventilation drives latent load—ensure L/s-person matches your standard and occupancy.
  • Don’t ignore glazing. If you know SHGC and orientation, adjust the solar factor to capture sun peaks.
  • Compare SHR. If SHR is too low (very humid), expect larger coils or dedicated dehumidification strategies.
  • Export the report. Use the built-in report to log assumptions for audits and handover.

Related reading

Psychrometrics: Moist Air Made Easy Key Thermodynamic Properties Ductwork via Bernoulli (Step-by-step) Duct Design Calculator (ASHRAE) Pipe Design: Head Loss & Fittings
Methodology & standards notes

The calculator uses steady-state envelope conduction, solar window gains, internal sensible/latent, and ventilation/infiltration loads. Humidity ratio is estimated with a Magnus–Tetens saturation curve. Airflow is a rule-of-thumb conversion from TR. When you pick a standard (ASHRAE / ISHRAE / CIBSE), the tool pre-fills indicative U-values, set points, and ventilation starters and shows: “Values derived from <Standard>, clause <xx> (user must verify).”

Ideas to make readers stay longer

  • Add a short **30-sec screen-capture** GIF of you using the tool (inputs → results → report).
  • Drop in a **“Preset of the Week”** box (e.g., Kitchens vs. Restaurants) with a one-click apply button.
  • Embed a quick **quiz** (“Which input affects latent load the most?”) and reveal answers with `
    `.
  • Show a mini **before/after**: change only ventilation and let readers see the latent spike.
  • End with a **downloadable report** generated from the tool—people love shareable outputs.

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