HVAC for commercial and industrial buildings: loads, system choices, efficiency, controls and maintenance

Heating, ventilation and air conditioning, usually shortened to HVAC, keeps offices, factories, warehouses, shops and clinics comfortable, healthy and productive. It is also, in many commercial buildings, the largest single user of electricity and the biggest source of complaints: too hot by the windows, too cold in the meeting room, stuffy in the afternoon, noisy at night. Industrial sites add process heat, fumes, dust and large doors to the challenge.

Many HVAC problems are not caused by faulty equipment. They come from systems sized for the wrong loads, controls set up badly or never tuned, heating and cooling fighting each other, ventilation that ignores occupancy, dirty filters and coils, and maintenance that responds to breakdowns rather than preventing them. Building owners and managers who understand the basics can ask better questions of designers and contractors, spot waste and make sound investment decisions.

This article explains how heating and cooling loads arise, the main system types and where each suits, how efficiency is measured, how controls and ventilation affect comfort and energy, ways to reduce cooling energy, and what good maintenance involves, including refrigerants and cooling tower safety. It is general information for owners, facility managers, engineers and business managers. HVAC design and work must be carried out by suitably qualified and licensed people, to the National Construction Code and relevant Australian Standards.

Understanding loads

An HVAC system exists to remove or add heat and moisture, and to supply fresh air. The cooling load comes from:

• Conduction through walls, roofs, floors and glazing when it is hotter outside.
• Solar gain through windows and onto roofs, often the largest single load in offices with large glazed areas.
• Infiltration and ventilation: hot, humid outside air entering through gaps, doors and intended ventilation.
• People: each person gives off roughly 100 to 150 watts of heat, depending on activity, partly as moisture.
• Lighting and equipment: computers, machines, ovens, compressors and lights all add heat.
• Processes: in industrial buildings, process heat can dominate everything else.

Loads have two parts. Sensible heat raises temperature; latent heat is moisture that must be removed to control humidity. Humid climates and crowded spaces have high latent loads, which affect system choice.

Heating loads come from heat lost through the building fabric and to incoming outside air, reduced by internal gains from people, lights and equipment.

Units

Australian practice uses kilowatts for heating and cooling capacity. Equipment and documents from other countries may use British thermal units per hour or tons of refrigeration. One kilowatt is about 3,412 BTU per hour, one ton of refrigeration is about 3.517 kW, and one kilowatt is about 860 kilocalories per hour. Mixing these units in older drawings and imported documentation is a common source of error, so convert carefully and check results for plausibility.

System types

Industrial buildings often need different approaches: spot cooling at workstations, evaporative cooling of large spaces, make-up air to replace air removed by exhaust systems, destratification fans to bring warm air down in winter, and process cooling separate from comfort systems.

Measuring efficiency

The efficiency of cooling equipment is expressed as the ratio of cooling delivered to electricity used. A coefficient of performance (COP) of 3.5 means 3.5 kW of cooling for each kilowatt of electricity. The energy efficiency ratio (EER) is a similar measure, sometimes quoted in different units. Because equipment usually runs at part load, seasonal or part-load ratings say more about real energy use than full-load figures. Air conditioners sold in Australia must meet minimum energy performance standards.

The difference matters. A building with an average cooling load of 100 kW for 2,500 hours a year uses about 83,300 kWh of electricity for cooling at a COP of 3.0, costing about $20,800 a year at 25 cents a kilowatt-hour. At a COP of 4.5, it uses about 55,600 kWh, costing about $13,900, a saving of about $6,900 a year for the life of the equipment.

Comfort is more than temperature

People’s comfort depends on air temperature, the temperature of surrounding surfaces, humidity, air movement, clothing and activity. A person near a hot window or a cold slab feels uncomfortable even when the air temperature is correct; gentle air movement makes warmer air feel comfortable; high humidity makes the same temperature feel oppressive. International standards such as ISO 7730 describe how these factors combine. Treating comfort only as a thermostat setting leads to over-cooling and complaints at the same time. Surveys of occupants, simple measurements of temperature and humidity at desks and workstations, and attention to radiant heat and draughts often solve complaints that bigger equipment would not.

Ventilation and air quality

Buildings need outdoor air to dilute carbon dioxide, odours and pollutants from people, materials and processes. AS 1668.2 sets out minimum ventilation requirements for many building types, and the National Construction Code references it. Too little ventilation causes stuffiness, drowsiness and health complaints; too much wastes energy heating or cooling outside air.

Demand-controlled ventilation, which adjusts outdoor air to occupancy, often using carbon dioxide sensors, saves energy in spaces with variable occupancy such as meeting rooms, training rooms and auditoriums. Filtration protects equipment and improves air quality; higher-grade filters need more fan energy, so balance filtration with fan capacity. Industrial exhaust systems for fumes and dust must be designed for capture, not just general ventilation.

Controls: where most waste hides

Good equipment wastes energy when controls are poor. Common problems include:

• Setpoints too low in summer or too high in winter. Each degree matters; cooling to 21 °C when 23 or 24 °C would be comfortable increases energy use substantially.
• Heating and cooling fighting each other when deadbands are too narrow or different zones have conflicting setpoints.
• Systems running when buildings are empty, because schedules were never set or were overridden and forgotten.
• No economy cycle, so the system runs refrigeration even when cool outside air could do the job.
• Fans and pumps at constant speed when variable speed drives could match output to demand.
• Sensors in the wrong places, such as near heat sources or in sun.

A building management system can schedule, monitor and optimise HVAC, but only if it is set up, tuned and checked. Many buildings have one that nobody uses well. Regular tuning, reviewing schedules, setpoints, faults and energy data, typically pays back quickly.

Reducing cooling energy

The cheapest cooling is the cooling a building does not need. In order of priority:

1. Reduce loads: external shading, better glazing, insulation, light-coloured roofs, efficient lighting and equipment.
2. Use natural and free cooling: economy cycles, night purging of heat with cool night air, and thermal mass to absorb daytime heat.
3. Use low-energy cooling where the climate suits, such as evaporative cooling in dry regions.
4. Extend comfort: ceiling fans allow higher temperature setpoints with equal comfort, and people tolerate wider ranges when they have some control.
5. Choose efficient equipment and size it correctly, avoiding large margins that make it run inefficiently at part load.

The cutting energy use in business premises article covers broader energy savings in buildings.

Maintenance

Good maintenance keeps systems efficient, reliable and safe:

• Filters changed or cleaned on schedule.
• Coils cleaned, since dirty coils cut capacity and efficiency.
• Condensate drains kept clear to prevent water damage and microbial growth.
• Belts, bearings and motors inspected; the maintenance that prevents breakdowns article covers planned maintenance routines.
• Refrigerant leaks checked and repaired.
• Controls and sensors calibrated.
• Performance monitored through energy use and temperatures, so declining efficiency is noticed.

Refrigerants

Refrigerants must be handled by appropriately licensed technicians, and leaks harm both performance and the environment. Australia is phasing down the use of high global-warming-potential refrigerants, and newer systems use alternatives such as lower-impact synthetic refrigerants, carbon dioxide, ammonia or hydrocarbons. Some alternatives are flammable or toxic, or operate at high pressures, so they bring their own safety requirements. Consider refrigerant type and future availability when buying equipment.

Cooling towers and Legionella

Cooling towers and evaporative systems can grow Legionella bacteria, which cause a serious form of pneumonia. Australian requirements include AS/NZS 3666 and state and territory regulations, which in many places require registration, risk management plans, water treatment, regular testing and inspection. Building owners are responsible for compliance.

Buying and replacing systems

Compare options on whole-of-life cost: purchase and installation, energy, maintenance, refrigerant, expected life and replacement. Ask designers to size systems from calculated loads, not rules of thumb, and to consider future changes in use. Require proper commissioning, testing that the installed system performs as designed, and handover documentation including as-built drawings, settings and maintenance manuals. The buying for the whole life of equipment article covers whole-of-life purchasing.

A worked example

This is an illustrative example. A manufacturer occupies a building with offices and a light production area. Staff complain of cold offices in summer and hot production areas, and electricity bills have risen. An HVAC contractor and the facilities manager carry out a review.

Findings.

• Office cooling setpoints are 20 °C, while heating in some zones starts at 21 °C, so heating and cooling run at the same time.
• The building management system runs air handlers 24 hours a day, every day, because a schedule was overridden during a project two years earlier.
• The economy cycle is disabled after a faulty damper actuator was never replaced.
• Office coils are heavily fouled, and filters are overdue.
• Air handler fans run at constant speed.
• The production area relies on a few wall exhaust fans, with no spot cooling at hot workstations.

Actions.

• Setpoints reset to about 23 to 24 °C for cooling and 20 to 21 °C for heating, with a deadband to prevent fighting.
• Operating schedules restored to match working hours, with an after-hours button for occasional use.
• The damper actuator replaced and the economy cycle re-enabled.
• Coils cleaned and a filter schedule set.
• Variable speed drives fitted to air handler fans.
• Evaporative spot coolers and ceiling fans added in production.

Result. HVAC electricity use falls by about 30%, comfort complaints drop sharply, and the work pays back in under two years. The business sets up a monthly review of building management system alarms, schedules and energy data.

Applying this in an Australian business

• Understand your loads before buying or changing systems.
• Choose systems for the building, climate and use.
• Compare efficiency on part-load performance and whole-of-life cost.
• Ventilate to standards, adjusting for occupancy.
• Tune controls: setpoints, deadbands, schedules and economy cycles.
• Reduce loads first with shading, insulation and efficient lighting.
• Maintain filters, coils, drains and controls.
• Manage refrigerants and cooling towers with licensed contractors and compliance plans.

Where HVAC goes wrong

• Systems sized by rules of thumb, with large margins.
• Heating and cooling fighting each other.
• Plant running when buildings are empty.
• Disabled economy cycles and broken dampers.
• Dirty coils and overdue filters.
• Building management systems nobody monitors.
• Cooling towers without proper water treatment and records.

Questions to ask about your HVAC

• What are our main heating and cooling loads, and how could we reduce them?
• What setpoints, deadbands and schedules are in use, and who checks them?
• Is the economy cycle working?
• How efficient is our equipment at part load, and how old is it?
• When were filters and coils last serviced?
• Are our cooling towers registered, treated and tested as required?

Bringing it together

HVAC performance depends on understanding loads, choosing suitable systems, tuning controls and maintaining equipment well. Reduce loads first, use free and low-energy cooling where the climate allows, and choose efficient equipment sized from calculation. Ventilate to standards while adjusting to occupancy, keep controls tuned and maintain filters, coils and drains. Manage refrigerants and cooling tower risks with licensed people and proper records. The result is a building that is comfortable and healthy, costs less to run and avoids unpleasant surprises.

---

Source: KEVOS editorial notes, drawing on earlier KEVOS study material on HVAC engineering, heating components and controls, school and commercial HVAC design, low-energy cooling for buildings and building services engineering, together with established building services practice. The worked example is illustrative. This article is general information; HVAC work must be done by qualified, licensed people.