HVAC and Ventilation Equipment Selection Guide: Chillers, AHUs and Fans

In an HVAC investment, equipment price is a small part of the ten-year cost. Efficiency figures decide the outcome: raising chiller COP from 2.8 to 3.6 cuts electricity for the same cooling load by roughly a quarter. Selection therefore has to weigh efficiency alongside capacity.

Chiller Selection and Efficiency

Water-cooled chillers are more efficient than air-cooled units but require a cooling tower and water circuit. Air-cooled chillers are simpler to install and dominate small and mid capacities. Industrial applications most often fall between 50 kW and 2,000 kW. Efficiency is expressed as COP and EER, while seasonal figures (SEER, SCOP) better reflect real operation because they include part-load behaviour.

Part-Load Performance

A cooling system spends most of its life between 40 and 70 percent load, not at full load. Inverter and multi-stage chillers are markedly more efficient in that band than fixed-speed units, which is why part-load metrics such as IPLV or ESEER can matter more than full-load COP.

Equipment Classes Compared

Equipment	Capacity range	Efficiency metric	Service interval	Expected life
Air-cooled chiller	50-1,200 kW	EER 2.6-3.4	Every 6 months	15-20 years
Water-cooled chiller	150-3,000 kW	COP 4.5-6.0	Every 6 months	20-25 years
Air handling unit	1,000-100,000 m³/h	Fan SFP	Filters 3-6 months	20-25 years
Cooling tower	100-5,000 kW	Approach 3-5 K	Annual cleaning	15-20 years
Air-source heat pump	10-500 kW	SCOP 3.0-4.5	Annual	15-20 years

Air Handling and Ventilation

The first figure to establish for an AHU is airflow. It follows from room volume and required air changes per hour: 4-6 in offices, 6-15 in production areas, and considerably more in kitchens and laboratories. Filter class is the other critical choice; under ISO 16890, ePM1 50-70 percent is common for general applications. Heat recovery units return 60-85 percent of the energy in exhaust air and cut heating and cooling loads substantially.

Used HVAC Equipment Checklist

1. Check the refrigerant type; units running phased-out gases can be hard and costly to service.
2. Read compressor running hours and start counts; frequent cycling consumes compressor life.
3. Inspect condenser and evaporator fins for corrosion, damage and fouling.
4. Have pressures measured under load; abnormal discharge pressure indicates fouling or a refrigerant issue.
5. Carry out a leak test and require documented proof that the system holds charge.
6. On air handling units, check fan bearings, belts, damper linkages and panel insulation.
7. Confirm the controls, including BMS compatibility, work and are still supported.
8. Budget dismantling, transport, recharging and commissioning from the outset.

Daikin, Carrier, Trane, Mitsubishi Electric, Systemair, Alarko, Üntes and Friterm are commonly encountered manufacturers in this segment.

Energy and Operating Cost

HVAC can account for 30-50 percent of total plant electricity. A facility with a 500 kW cooling load draws about 167 kW with an EER 3.0 system; moving to EER 4.0 brings that down to 125 kW. Over 2,500 operating hours a year, the difference is roughly 105,000 kWh. Add filter replacement, water treatment chemicals, tower cleaning and annual service. Plants with process cooling loads should evaluate them together with equipment listed under plastics and rubber machinery and food processing machinery.

Controls, Commissioning and Water Treatment

In HVAC, savings come more from control than from equipment. With a building management system running outdoor-reset water temperature, night setback, zone-level control and free cooling, annual energy consumption can fall by 15-30 percent. The same chiller consumes far more in a poorly controlled system than in a well-controlled one.

Commissioning also shapes the result. Unbalanced water flows are the most common and most easily overlooked system-side fault; on an unbalanced circuit some zones overcool while others are undercooled, and total consumption rises for no benefit.

Water treatment determines the life of water-cooled systems. If scale, corrosion and biological growth are not controlled in the cooling tower circuit, condenser efficiency falls, discharge pressure rises and compressor load increases. A scale layer of just 0.5 millimetres measurably degrades heat transfer, so treatment chemicals and regular analysis belong in the fixed operating budget.

Finally, weigh spare parts and service access. Lead times for compressors, plate exchangers, fan motors and control boards can turn a mid-summer failure into weeks of lost production or comfort. For critical process cooling in particular, favour brands with a local service network.

New or Used?

In HVAC, annual running hours and refrigerant regulation decide. On continuously running systems, the efficiency gap repays a new unit within a few years; for standby and seasonal duty, used equipment is an economical answer.

Criterion	New machine	Used machine
Initial investment	High	Substantially lower
Lead time	8-30 weeks after order	Usually 1-3 weeks
Warranty and service	Manufacturer warranty, commissioning included	Limited or dealer warranty
Technology and efficiency	Inverter compressor, low-GWP refrigerant, BMS integration	One or two generations behind
Spare parts	Secured for many years	Depends on model age
Depreciation	Steep loss in the first years	Much slower value loss
Finance and leasing	Suits leasing and incentives	Limited, needs appraisal

A new chiller runs far more efficiently at part load than an older generation thanks to its inverter compressor, cutting annual consumption noticeably. It arrives charged with low global warming potential refrigerant, which removes future supply problems. BMS integration supports free cooling and zone-level control out of the box.

What to ask when buying new matters just as much as the used checklist:

• Lead time: the schedule from order confirmation to commissioning must be in writing.
• Warranty scope: duration, excluded parts and response time should be stated clearly.
• Service network: ask the distance to the nearest authorised service and its response time.
• Parts commitment: stock status and lead time for critical parts belong in the contract.
• Training and commissioning: confirm operator training and acceptance tests are included in the price.

Frequently Asked Questions

How do I calculate chiller capacity?

Add internal heat gains (solar, lighting, equipment, occupants) and process loads, add the fresh air load, then apply a 10-15 percent margin. As a rough sanity check, offices run 90-130 W of cooling load per square metre.

Air-cooled or water-cooled?

Below 500 kW, and where no water infrastructure exists, air-cooled chillers are practical and economical. In high-capacity, continuously running plants, water-cooled systems recover the extra investment within a few years through higher efficiency.

Is buying a used chiller sensible?

Yes, if compressor hours are reasonable, the leak test is clean and the refrigerant is still available. The risky units are those charged with phased-out gases and compressors with very high start counts, where conversion adds cost.

How much does heat recovery save?

Plate and rotary heat recovery units return 60-85 percent of the energy in exhaust air. In facilities with high fresh air requirements, that translates into a very significant reduction in heating and cooling load.

How do I choose a filter class?

ePM1 50-70 percent is sufficient for offices and general areas. Hospitals, cleanrooms and pharmaceutical production require HEPA filtration. Higher filter classes raise pressure drop and fan energy, so specify to need rather than by default.

Does refrigerant regulation affect used purchases?

Yes. On a unit charged with a phased-down refrigerant, future gas supply becomes expensive and difficult. When buying a used chiller, confirm the refrigerant is still freely available, otherwise budget for a conversion.

To review new and used chillers, air handling units, cooling towers, fans and heat pumps, browse the HVAC and ventilation equipment category.