What is heat recovery ventilation & why is it necessary?

Why Do We Need Heat Recovery Ventilation?

Heat Recovery Ventilation isn’t widely used in Australia yet but that doesn’t mean we don’t need it.  According to the Australian government’s Your Home website, 15-25% of heat loss from buildings is caused by air leaking out of the building. Air leakage makes buildings more difficult to heat and so they are less energy efficient. Not only is this bad for the environment, heating an unsealed building also costs more money. As Australians become more energy conscious, they seal more of the little cracks around windows and doors that let the air escape from the building. New buildings are also often built with insulation and efficiency in mind. This makes sense, especially because heating and air conditioning continue to drive up energy bills. Stopping air leakage helps households and businesses take control of their expenses. But sometimes solving one problem creates another. Although sealing the building stops warm air from leaking out, fresh air can’t come in either!

Why We Need Ventilation: A Quick Reminder

Preventing fresh air from entering reduces the air quality in the room, making it stale. This is partly because humans breathe in oxygen and breathe out carbon dioxide. Sealing a building to increase energy efficiency stops the carbon dioxide from flowing outside and oxygen from flowing in to replace it. This means that a poorly ventilated building will have a higher concentration of CO2 than a building with good ventilation. We breathe out moisture as well as carbon-dioxide. Households also create moisture from use of showers, cookers and laundry appliances (just a few examples). As moisture builds up inside, it creates condensation which can lead to mould growth. All of this is bad for the air quality if there isn’t any new air coming in to push the old air out. Of course, opening a window swaps the old stale air for fresh new air. But this undoes all the time and effort already invested in sealing the building. In Winter months, opening a window cools a space very quickly. Heat recovery ventilation systems offer a solution by allowing fresh air to enter a building without letting cool air affect the inside temperature.

How does a Centralised (Whole House) Heat Recovery Ventilation system work?

A centralised Heat Recovery Ventilation System has several elements:

  • An incoming vent in at least one room of the building
  • A corresponding outgoing vent for each incoming vent
  • An air handling unit with heat recovery.

The incoming vents bring in fresh air from outside the building. As the air comes in through the roof, it passes through the heat exchanger. At the same time the stale (but warm) air is flowing in the opposite direction from inside the house. It also passes through the heat exchange mechanism, but it does not mix with the cool fresh air. Instead the two types of air pass alongside each other in separate pipes. The warm air from inside the building heats the fresh cool air from outside. The fresh air is now warm and flows into the building. There you go! You can stay cosy and breathe fresh air!

How does Decentralised (Single Room) Heat Recovery work?

Decentralised Heat Recovery works to achieve the same aim as a centralised system: providing a source of ventilation without sacrificing heat. Instead of ventilating the house from one central point, it operates on a smaller scale which makes it possible to address energy efficiency room by room. Depending on your property you may choose to install a unit for ventilation from a single point or multiple units for installation at several points. The best choice will depend on the size of your property as well as how you use it. At present, we carry a decentralised heat recovery unit which doesn’t need a lot of space for installation. This unit works in short cycles which automatically switch over during operation. On the first cycle, it draws out the stale air and moisture from inside the property. As the air passes through the unit, the unit retains the air’s heat. By operating in cycles, a small unit is able to facilitate air exchange without mixing the incoming and outgoing air streams. Once it switches to the second cycle, it then transfers the heat to incoming fresh air. Decentralised heat recovery is a fantastic option for renovations or retrofits, especially for small or older dwellings, because they need less space. Installing several units throughout the property will create a similar outcome to a centralised system. To get the best use out of decentralised heat recovery, you will still need to seal the space your are working on to prevent air leakage.

How effective is a Heat Recovery Ventilation system?

It’s not yet possible to preserve all of the heat energy as it passes through an HRV, but the technology continues to get better. At Universal fans we carry a range of heat recovery units that incorporate the latest technology. Because they aren’t widely used in Australia yet, it’s difficult to say how the energy savings might translate onto a gas or electricity bill. But HRV systems are already common in Europe. Over there, the general consensus is that they reduce heating costs but it will take time to offset the cost of installation. It’s also worth remembering that just sealing a building reduces energy costs by up to 20 per cent, according to a 2006 report by the Sustainable Energy Authority of Victoria. But a sealed building without any ventilation is unpleasant to live or work in.

Is an HRV system right for your home or business?

Like any other product, it depends on your situation. First, a building needs good insulation to get the most out of a Heat Recovery Unit. Second, a Heat Recovery Ventilation System works best in airtight buildings where there isn’t any air leakage. If your home or office is already draughty, then a heat recovery ventilation system won’t stop the cool air coming in through gaps and cracks that are already in the building’s structure. If you are considering an HRV system for an older building, then patching up these gaps is the best way to get the most out of it. Building airtight structures to conserve heat energy is a relatively new practice, so it can be hard to find all of the leakage points. Heat Recovery Ventilation systems are great for buildings with low air leakage. If you are in the process of making your building energy efficient then contact us to ask about a Heat Recovery Ventilation system. We also take enquiries for new builds.


Further Reading

Mechanical ventilation with heat recovery: Fresh air without the heat loss (or gain) Australian Passive House Association Heat Recovery: A guide to key systems and applications