Tips for energy-efficient HVAC design

Air conditioning fans

As energy costs continue to rise, your customers need to take advantage of energy-saving opportunities in HVAC systems. How much energy does heating and cooling use? On average, HVAC energy consumption in commercial buildings accounts for around 51% of energy costs.

HVAC efficiency involves minimising energy input. To accomplish this, your design can optimise ventilation, zone control, heat recovery and operations.

Let’s say you’re planning energy efficient HVACs systems for commercial buildings. The first step is to consider where the loads originate from:

  • Building envelope
  • Lighting
  • Occupancy
  • Equipment being used
  • Ventilation

You can’t just design heating and ventilation for energy efficiency alone. You must also consider air quality, which you can learn about in Designing HVACs: What should you know about indoor air quality?

Ventilation load depends on either the number of occupants or the mechanisms used to control particulate matter (PM). One strategy for energy conservation is using the ASHRAE mechanical room-ventilation rate. This is done through demand-control ventilation as set out in ASHRAE Standard 62.1, but the climate of where the HVAC will be installed plays a key role.

Using available environmental resources is fundamental to energy-efficient HVAC systems. You should also look at technologies that not only improve occupant’s comfort and indoor air quality, but also reduce energy use.

Improve HVAC efficiency with zone control

If you’re designing for a facility that requires high ventilation rates, most of HVAC energy use is reheat. This is the heating that takes place after cooling the supply air, which is done to avoid overcooling an area. Many HVAC systems consume excessive amounts of energy for reheat by as much as 50% more than is necessary. How do you minimise reheat?

Efficient heating and cooling systems are incorporating zone control to almost eliminate reheat. Zone control allows the end user to control the temperature in each room. Unoccupied rooms don’t have to be heated or cooled at the same temperatures as occupied areas. Controlling how much heating and cooling is done at the zone level almost eliminates reheat and reduces cooling energy.

This energy-saving heating and cooling system is not cheap. However, zone control just might be the most cost-effective HVAC systems. They pay for themselves in the long run, reducing energy costs by up to 25%.

HVAC energy conservation: heat recovery

Heat recovery in efficient HVAC systems typically exchange heat between discharged air within a room and air introduced from outdoors. The system might exchange only sensible heat or both sensible and latent heat. This type of heat-recovery system preheats and/or pre-cools ventilation air, which reduces the system load. This is typically accomplished by putting the two airstreams through a heat exchanger.

A sensible heat exchange can look like this:

Counter flow plate heat exchanger

This psychrometric process illustrates an increase in the incoming air’s sensible heat that could occur in a:

  • Cross-flow plate heat exchanger;
  • Regenerative thermal wheel; or a
  • Run-around coil

This is a basic sensible heating or cooling process, depending on the opposing airstreams’ temperatures.

  • The heat exchanger sensible heat effectiveness: εS = ṁO(θB – θO)/ṁR(θR – θO), where ṁO and ṁR are the respective air mass flow rates of air at outdoor temperature θO
  • Room temperature: θR
  • Temperature of outdoor air after going through the heat exchanger: θB

If the temperature of the incoming air, θO, is below the dew-point temperature of the extracted air, θRdp, condensation in the airstream coming from the occupied space will occur, providing increased heat exchange.

HVAC energy-saving technologies

The best energy-efficient HVAC systems rely on technologies you should consider before you begin your design. You can help your customers save energy heating and cooling with these methods:


What it does

Why it’s energy efficient

Demand controlled ventilation

Combines economisers to maintain desired air levels with carbon dioxide sensors

Avoids over ventilating, which wastes energy

Dedicated outdoor air systems

Improves humidity control by conditioning outdoor air apart from indoor return air

Removing moisture from external air reduces load on the cooling system

Displacement ventilation

Uses a low-velocity stream of fresh, cool air at floor level, displacing stagnant air near ceiling

Improves indoor air quality while saving energy

Electronically commutated motors

Lowers electrical heating and cooling consumption, helping to maintain proper air flow through the system

Saves energy by varying HVAC blower speed as needed

Zero-degree heat pumps

Transfers heat from outside air to an indoors – even when temperatures fall to 0°F

Moves heat instead of creating it

Energy recovery ventilation (ERV)

Exchanges energy contained in exhausted air and uses it to treat incoming outdoor ventilation air

Saves energy by reducing the HVAC’s needs, yet maintains comfortable air quality levels

Desiccant dehumidification

Removes moisture from the air with a desiccant and evaporates it with heat

Removing humidity and precooling air reduces air conditioning load, saving energy

Duct sealing

Aerosol systems seal leaks and should be used as needed during maintenance

Prevents leakage to avoid energy waste

Microchannel heat exchangers (MCHE)

At least one fluid, typically refrigerant or water, flows through tubes or enclosed channels. At the same time air flows cross-current through connected fins

Extremely efficient, but involves high initial cost

Thermal energy storage

Cools by extracting heat from ice or chilled water during peak hours

Electricity is used during off-peak hours, which reduces costs

Chilled beam cooling

Uses cool water in coils that exchange heat with room air

Moves heat around a building efficiently and reduces energy use

Variable speed drives (VSD)

Adjusts the speed of motors based on the HVAC load requirements and operation schedule

Significantly reduces energy consumption

Variable flow volume (VFV)

Large-scale, ductless system uses multiple compressors, providing part-load performance and zoned temperature control

Works at the needed rate, which enables substantial energy savings at load conditions

What else should you know before designing an HVAC? Be sure to also read about:

Designing for easy maintenance

Vibration isolation


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Download free CADs and request free samples, which are available for most of our solutions. It’s a great way to ensure you’ve chosen exactly what you need. If you’re not quite sure which product will work best for your energy-efficient HVAC equipment, our experts are always happy to advise you. You should also check out our Quick guide: the small HVAC components for your design. Whatever it is you need, you can depend on fast despatch.

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