Understanding What You Actually Need Before You Buy Anything

Most chiller procurement decisions go wrong before a single specification is written, because the person making the purchase has not clearly defined what the chiller is supposed to do. This sounds obvious, but in practice it happens constantly — a purchase order gets raised based on a rough floor area estimate, or someone copies the spec from a previous project at a different site, and the resulting system is either undersized or so oversized it spends its entire working life running at 30% load, burning far more electricity than it should.

So before you look at any equipment, answer these questions with precision:

The answers to these questions form the brief that every subsequent decision flows from. Without them, you are making expensive guesses with someone else's equipment budget.

Cooling Load Calculation — Getting the Numbers Right

The cooling load calculation is the single most important technical step in the entire chiller selection process. It determines the capacity of the chiller you need, measured in tonnes of refrigeration (TR) or kilowatts (kW). An undersized chiller will never keep up with demand. An oversized one will short-cycle, wear out faster, consume disproportionate energy at part-load, and cost significantly more to purchase than necessary.

There is a common temptation to apply a simple rule of thumb — "one tonne per X square metres of floor area" — and call it done. In light, uniform office spaces with standard glazing, this approach produces a roughly adequate number. In a factory with significant process heat loads, a data centre with dense server racks, a kitchen with cooking equipment, or a building with unusual solar exposure, rule-of-thumb numbers can be off by 30, 40, or even 50 percent. The only right way to calculate cooling load is through a proper heat gain analysis that accounts for every heat source in the space.

What Goes Into a Proper Load Calculation

A thorough cooling load calculation for a building or facility accounts for the following heat gain components. Each one matters, and each one requires actual data from your specific site rather than generic assumptions:

Solar heat gain through glazing and walls — varies enormously by orientation, glass type, and shading. A west-facing glass facade on a factory in Rajasthan generates a very different solar load from the same facade in a shaded industrial park in a cooler climate.

Transmission heat gain through the building envelope — walls, roof, floor, and windows. Insulation quality, wall construction, and roof type all affect this number significantly.

Ventilation and infiltration loads — the heat brought in by outside air through the ventilation system and through gaps in the building envelope. In humid climates, the latent (moisture) component of this load can be as large as the sensible (temperature) component.

Internal heat gains — people generate heat (roughly 70–100W each at rest, significantly more if working physically), lighting generates heat, and equipment generates heat. In an office building, IT equipment is typically the dominant internal heat source. In a factory, process machinery may dwarf everything else combined.

Process loads — if the chiller is serving a process rather than or in addition to a building, the heat generated by the process itself must be precisely measured or calculated from equipment manufacturer data rather than estimated.

For any installation above 20 TR, a proper load calculation should be performed by a qualified HVAC engineer using recognised calculation methodology such as ASHRAE's Heat Balance Method or the Cooling Load Temperature Difference (CLTD) method. The cost of this engineering is trivial relative to the cost of a wrongly sized chiller plant.

Air-Cooled vs. Water-Cooled: The Real Decision

Once you know your cooling load, the next major decision is how the chiller will reject its heat — through air or through water. This choice has substantial implications for capital cost, operating cost, space requirements, maintenance complexity, and environmental impact. It is not simply a technical preference — it is a strategic decision that should be made with full awareness of the trade-offs.

The general guidance from an energy efficiency perspective is that for installations above 100–150 TR where the chiller will operate for many hours annually, the higher capital cost of a water-cooled system is typically recovered through energy savings within 3–5 years. Below that threshold, or for installations with limited annual operating hours, the simpler air-cooled configuration often makes more practical sense.

Water availability and quality is an important additional consideration. If your site is in a water-scarce region or has very high TDS source water, the operating cost and complexity of managing a cooling tower water circuit can shift the economics significantly in favour of air-cooled equipment — even at larger capacities.

Chiller Types and When to Use Each

Within the air-cooled and water-cooled categories, there are further choices to make based on the compressor technology. Each compressor type has different efficiency characteristics, capacity ranges, part-load performance, and maintenance profiles. Understanding the basics helps you ask the right questions when evaluating supplier proposals.

Screw Chillers

Screw chillers use twin helical rotors to compress refrigerant. They are the workhorses of the industrial and commercial chiller market — robust, relatively simple, available from 30 TR to 500+ TR, and competitively priced. Modern screw chillers with variable speed drives have excellent part-load efficiency. They are the default choice for most medium to large industrial process cooling applications and are well-suited to the 24/7 operating profiles common in manufacturing. Maintenance is moderate and well-understood — screw elements require periodic oil analysis and occasional bearing replacement.

Centrifugal Chillers

Centrifugal chillers use a high-speed impeller to accelerate refrigerant vapour, converting velocity to pressure. They are the most energy-efficient option at or near full load in large capacities — typically above 200 TR — and are the standard choice for large commercial buildings, district cooling plants, and major industrial facilities. Their efficiency advantage is greatest at full load; at part load, efficiency drops more steeply than screw chillers unless magnetic bearing technology or variable speed drives are incorporated. Centrifugal chillers have fewer wearing parts than reciprocating or screw machines and can have very long service lives when properly maintained.

Scroll Chillers

Scroll chillers use two spiral-shaped scrolls to compress refrigerant. They are quiet, vibration-free, and simple — but limited to smaller capacities, typically below 60 TR. Scroll chillers are widely used in commercial buildings, small process applications, and modular chiller configurations where multiple small units are combined to achieve larger capacity with redundancy. They have fewer moving parts than screw or reciprocating machines and are generally lower maintenance.

Absorption Chillers

Absorption chillers use heat rather than electricity as their primary energy input — typically waste heat from a process, steam, or hot water. They are the right choice when significant waste heat is available (above 80–90°C), electricity is expensive or scarce, or a facility wants to improve overall energy utilisation through combined heat and power (CHP) integration. Absorption machines have no compressor, move very few mechanical parts, and can be remarkably reliable — but they require more careful water chemistry management and are significantly larger per tonne of cooling than vapour compression chillers.

The Pre-Purchase Checklist

Before committing to a purchase order, work through this checklist systematically. Each item represents a decision point where inadequate attention creates problems that are far more expensive to fix after the equipment arrives than before.

Site Preparation Checklist

A chiller that arrives at a site that is not ready for it is an extremely expensive problem. Equipment sitting on a construction site waiting for civil work to complete ties up capital, risks damage, and delays production. Work through site preparation in parallel with equipment procurement so the two converge at the same time.

Installation Checklist

The installation phase is where specification decisions meet physical reality. Experienced installation teams will follow manufacturer guidelines closely — but as the facility owner or project manager, you should know what to look for and what questions to ask. A poorly executed installation can compromise a well-specified chiller for its entire working life.

Commissioning Checklist

Commissioning is the process of verifying that the installed system actually performs as specified. It is not the same as start-up. Start-up means the machine switches on. Commissioning means the machine switches on, operates safely, meets its specified capacity and efficiency, and all controls, safeties, and integrations function correctly. Commissioning should always be carried out by the chiller manufacturer's trained engineer, not by the installation contractor acting alone.

Water Treatment — The Step Most Chiller Owners Skip

This is where many technically sound chiller installations go quietly wrong over the years following commissioning. Chiller tube bundles — both evaporator and condenser — are precision heat exchangers. Their efficiency depends entirely on clean metal surfaces for heat transfer. Scaling, corrosion, biological fouling, and suspended solids all degrade this heat transfer, and the efficiency loss is insidious: it happens gradually, invisibly, and is often not noticed until the chiller is struggling to maintain setpoint on a moderately warm day or electricity bills have crept up noticeably.

For water-cooled chillers, the cooling tower water circuit is particularly critical. Open cooling towers are exposed to the atmosphere and continuously concentrate dissolved minerals through evaporation while also collecting airborne dust, pollen, and biological matter. Without active water treatment, the condenser water in a cooling tower circuit will scale, corrode, and — most seriously — support the growth of Legionella bacteria, a health hazard with significant legal implications.

Chilled Water Circuit Treatment

The closed chilled water circuit is less problematic than the open condenser water circuit, but it still requires attention. Dissolved oxygen in the system water causes corrosion of steel components — pipework, pump casings, and valve bodies. An appropriate corrosion inhibitor dosed at commissioning and maintained at the correct concentration prevents this. The system should also include a scale inhibitor if the make-up water has significant hardness, and a biocide to prevent biological growth in any stagnant sections of pipework.

The water quality of the make-up supply to the chilled water circuit matters. If your make-up water has high TDS, high hardness, or iron content, consider installing a softener or reverse osmosis system on the make-up line to reduce the dissolved mineral load entering the system. This is a relatively modest investment that significantly extends the service interval between tube bundle cleanings and reduces chemical consumption.

Cooling Tower Water Circuit Treatment

The cooling tower circuit requires active water treatment management, not just an initial chemical dose. The key parameters to monitor and control are: pH (typically maintained between 7.0 and 8.5), conductivity (controlled through blowdown to limit total dissolved solids concentration), calcium hardness (to manage scale risk), Langelier Saturation Index (LSI — the key scale/corrosion balance indicator), and biological counts (to control Legionella and other biological growth).

Water Treatment Checklist for Chiller Plants

Ongoing Maintenance Checklist

A chiller plant that is commissioned correctly and then neglected will degrade steadily and quietly until an expensive failure makes the neglect impossible to ignore. The maintenance schedule is not bureaucracy — it is the difference between a chiller that delivers 20–25 years of reliable service and one that is struggling at year 8 and replaced at year 12.