Chiller Retrofit Savings Calculator
Put a claimed chiller-plant efficiency gain into kWh and rupees before you commit to it. Enter how many hours a year the plant spends at each band of load, the existing and proposed plant kW/TR at those loads — over the same plant boundary — your tariff, the change in O&M cost and the installed cost.
What this tool estimates
Annual electricity and rupee savings from changing the plant's kW/TR in each operating bin, net of any change in O&M cost, and the simple payback when that net saving is positive.
What it cannot decide
- Whether the new plant will actually achieve the kW/TR you enter — that needs part-load selection data at your water temperatures, and measurement after commissioning.
- Whether the plant has the capacity or redundancy your load needs — size that separately.
- Savings in demand charges, contract demand or transformer capacity: only energy is valued.
- Tax, depreciation, financing, or how long either plant will last.
Result
One bin treats every operating hour as the same load at the same efficiency. Real plants spend most hours at part load, where kW/TR differs from the rated figure — split the year into bins if you have logged data.
Every bin uses the same pair of kW/TR figures, which treats efficiency as if it did not change with load. Use each bin's own figures: measured for the existing plant, part-load selection data at your water temperatures for the new one.
| Step | Value |
|---|
| Bin | TR | Hours | Existing kWh | New kWh | Saved kWh |
|---|
| Scenario | Net ₹ / year | Payback |
|---|
Method version 6 October 2026. A screening estimate, not a design: see the limits below.
Where each figure should come from
| Input | Defensible source | Weak source |
|---|---|---|
| Hours in each bin | A year of BMS trends, BTU-meter data or chiller log sheets, grouped by load | Run hours multiplied by an assumed average load |
| Existing plant kW/TR | Logged input kW of every item inside the boundary ÷ logged TR (BTU meter, or flow × temperature difference) | A nameplate figure, or one spot reading used for every bin |
| New plant kW/TR | Selection data at each part load and your design water temperatures, plus pump and tower-fan power at those loads | A full-load rating applied to every hour of the year |
| O&M change | Quoted AMC and consumables for both plants over the same scope | Left out because it is hard to estimate |
How this calculator works — and where it stops
What it calculates
The annual electricity and rupee saving from replacing or upgrading a chiller plant, worked out bin by bin from the cooling the plant delivers and its kW/TR before and after, net of any change in O&M cost — and the simple payback, only when that net saving is positive. A negative saving is shown as it is.
Inputs
- Plant boundary — chillers only; chillers and pumps; or chillers, pumps and cooling-tower fans. Both kW/TR figures must cover the same one.
- Operating bins: for each band of load, the cooling delivered (TR, or kW thermal converted at 1 TR = 3.516853 kW) and the hours per year the plant spends there. The bins are slices of one year, so their hours add up to at most 8,784.
- Existing and new plant kW/TR in each bin — electrical input kW of everything inside the boundary per TR delivered, at that load.
- Electricity rate per billed unit — ₹/kWh, or ₹/kVAh with the average billing power factor (kWh ÷ kVAh from the bills).
- Change in annual O&M cost — the new plant's minus the existing plant's; negative if it falls, 0 if unchanged.
- Installed cost of the retrofit.
Method
- For each bin: TR·h = TR × hours; existing kWh = TR·h × existing kW/TR; new kWh = TR·h × new kW/TR.
- Electricity saved = Σ TR·h × (existing kW/TR − new kW/TR). A bin where the new plant is worse adds a negative saving; nothing is clamped to zero.
- On a kVAh tariff, billed units saved = kWh saved ÷ the billing power factor.
- Value of the electricity saved = billed units saved × rate; net saving = value − change in O&M cost.
- Simple payback = installed cost ÷ net saving, reported only when the net saving is more than zero.
- Load-weighted kW/TR = plant kWh ÷ TR·h for each plant. Where O&M rises, the tool also shows the average improvement needed just to cover it: O&M rise ÷ (TR·h × ₹ per kWh).
- Sensitivity: the new plant 0.05 and 0.10 kW/TR worse than entered in every bin, 20% fewer hours, and the rate 10% lower and higher.
Assumptions
- Both plants deliver the same cooling in the same hours — the comparison is at equal delivered load, not equal running hours or equal nameplate capacity.
- Each bin's kW/TR is a fair average for that band of load. The finer the bins, the more closely the result follows the plant's part-load behaviour.
- The rate is the marginal energy charge and demand charges do not change. On a kVAh tariff, the saved energy is assumed to carry the billing-average power factor.
- The saving is the same every year: no tariff escalation, ageing or change in load is modelled.
Limitations
- It does not verify any kW/TR figure. Manufacturers' part-load data are normally stated at standard rating conditions; at your water temperatures, fouling and control sequence the plant can do better or worse.
- Interactions across the boundary are not modelled — a change that saves compressor power can add pump or cooling-tower fan energy outside a narrow boundary. Meter the widest boundary you can.
- It does not size the plant or check redundancy, refrigerant, electrical, structural or plant-room changes the retrofit needs.
- Simple payback ignores the time value of money, financing, tax and equipment life. For alternatives with different capital and running costs over time, compare present cost instead.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- Boundary: whole plant (chillers, pumps and cooling-tower fans)
- One bin: 100 TR delivered for 2,000 hours a year
- Existing plant 1.0 kW/TR; new plant 0.7 kW/TR
- Electricity rate ₹8 per kWh
- Change in O&M cost ₹0
- Installed cost ₹20,00,000
Working
- Delivered cooling = 100 × 2,000 = 2,00,000 TR·h.
- Existing plant electricity = 2,00,000 × 1.0 = 2,00,000 kWh; new plant = 2,00,000 × 0.7 = 1,40,000 kWh.
- Electricity saved = 2,00,000 − 1,40,000 = 60,000 kWh a year — 30% of the plant's electricity inside the boundary.
- Value = 60,000 × ₹8 = ₹4,80,000 a year; with no O&M change, the net saving is the same.
- Simple payback = ₹20,00,000 ÷ ₹4,80,000 = 4.17 years.
Result. ₹4.80 lakh a year net and a simple payback of 4.17 years, before any change in O&M cost. Because the example has one bin, the tool also flags that it treats the whole year as a single load point.
Sensitivity — what moves the answer
- Underperformance moves it most: if the new plant runs 0.05 kW/TR worse than claimed in every bin, the saving falls to 50,000 kWh and the payback stretches to 5.00 years; at 0.10 kW/TR worse, 40,000 kWh and 6.25 years.
- Hours pass straight through: 20% fewer operating hours gives 48,000 kWh and a 5.21-year payback.
- The rate moves the rupees, not the kWh: 10% lower gives a 4.63-year payback, 10% higher 3.79 years.
- An O&M rise of ₹1,00,000 a year cuts the net saving to ₹3,80,000 and the payback stretches to 5.26 years — the plant has to improve by 0.0625 kW/TR on average just to cover that rise.
How engineers use the result
To decide whether a retrofit proposal deserves a detailed study, and to write down what has to be true for its numbers to hold: the kW/TR the new plant must reach in each bin, over which boundary, and how much underperformance the payback can absorb. The bin table then doubles as the measurement plan after commissioning.
When a professional design must replace it
Before a purchase decision: the existing plant's kW/TR should come from logged power and cooling data over at least a full cooling season, the new plant's from part-load selections at your design water temperatures including pumps and tower fans, and the saving should be confirmed after commissioning by measurement over the same boundary.
Sources
- NREL, Uniform Methods Project — Chapter 14: Chiller Evaluation Protocol (NREL/SR-7A40-62431, September 2014) — the bin method (kWh per bin = tons × hours × kW/ton, for the baseline and the new plant); a chiller plant includes its pumps and cooling-tower fans; manufacturers' part-load data are typically at standard rating conditions, so use data adjusted to the design water temperatures where available
- BEE — Energy Efficiency Solutions for Existing Buildings: Commercial, four climates (study by TERI for the Bureau of Energy Efficiency, first printed February 2025) — Table 1 data to collect for a retrofit — chiller specification, chiller daily log book, annual plant operating hours, at least a year of electricity bills; simple payback and NPV/IRR to judge a retrofit, life-cycle cost for large investments over time
- BEE — Reports / Studies (retrofit and energy-efficiency publications) — the listing the BEE study above is published under
- 1 TR = 12,000 BTU/h = 3.516853 kW (thermal) — definition, used to convert kW thermal to TR
Questions people ask before using it
What information do I need before using this chiller retrofit calculator?
The hours the plant spends at each band of load over a year (from chiller log sheets, BMS trends or a BTU meter), the plant's input kW at those loads over a defined boundary — chillers, pumps and cooling-tower fans as metered — and the proposed plant's part-load kW/TR for the same boundary at your chilled- and condenser-water temperatures. Add the energy rate from your bill, the expected change in O&M cost and the installed cost.
Which site conditions could change the chiller retrofit savings?
Condenser-water and ambient wet-bulb temperatures, chilled-water set points, how the load is spread across the year, how several chillers are staged, a low chilled-water temperature difference, fouled condenser tubes and the way pumps and cooling-tower fans are controlled all move the real kW/TR. A plant that spends most hours at part load can perform very differently from its full-load rating, in either direction.
What should I send an engineer for a project-specific chiller retrofit review?
Twelve months of chiller log sheets or BMS trends, energy-meter readings for the chillers, pumps and cooling-tower fans, the plant schematic and equipment schedule with nameplates, recent electricity bills, the current O&M or AMC contract, and the proposed equipment's part-load performance data at your design water temperatures.
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