A healthy home is a sustainable home

Heat recovery ventilation can make homes dramatically healthier, and going a step further with heat pump ventilation can also offer energy efficient heating and cooling, says Clarissa Youden of Total Home Environment

With self-builders becoming more aware that they need to insulate and seal-up their homes to save energy, the environment and pocket, the air in their home can become more polluted than the air near a busy road. Several items inside your home emit a cocktail of chemicals called VOCs (Volatile Organic Compounds) which leach out of soft furnishings, chipboard, laminates, paint, plastics and room sprays.

If you’re renovating a home but not digging up the floors, radon gas is also a danger. Colourless and odourless, it is the second biggest cause of lung cancer in the UK, seeping out of the soil and getting caught inside homes.

To live in comfortable conditions, an adult needs approximately 30 m3 of fresh air per hour, meaning that two adults sleeping in a bedroom have less than an hour before CO2 and water vapour will build up with condensation and mould spores forming – worrying for Asthma sufferers. Plus, despite having eight hours sleep, you can wake up tired and your cognitive ability can be reduced significantly because you haven’t had clean air to breathe. You spend 70 per cent of your time at home and you breathe over 10,000 litres of air a day – don’t you want the cleanest, healthiest air in your home for you and your family?

Ventilating the home by poking holes through the skin with archaic technology – unfiltered trickle-vents in window frames (that people then shut because they’re too draughty) and noisy extractor fans in kitchens and bathrooms (which are never cleaned, so block-up) is not adequate. Opening windows also isn’t viable – to meet the 0.44 air changes per hour currently set by Building Regulations in England, you’d need to open all the windows for 10 minutes, every couple of hours – not particularly convenient and if you’re in a town do you want the noise and pollution inside? Plus, in all instances you’re throwing away vital heat.

This ventilation method contributes between 50-60 per cent of the typical heat-loss of a home, meaning half your heating bill goes to mitigating the effects of ventilation. So how do you guarantee good indoor air quality without losing heat? What types of ventilation are suitable?

Passive stack ventilation relies on natural air movement and a temperature difference inside and outside the home, so if it’s gusty there’s a risk of getting cold from over-ventilation and in the summer being stuffy, as temperatures are too similar in and outside for much air movement. Positive input ventilation relies on the house being leaky, so is not much good on the sustainability front. Mechanical extract ventilation relies on trickle vents, so you’re not only losing heat but it’s questionable whether you can guarantee that CO2 levels will be kept under the recommended 1,000 ppm level.

This is where heat recovery ventilation (HRV) comes into play. A low energy fan unit continuously extracts stale air out of wet rooms while drawing in fresh filtered air from outside. The two airflows pass each other in a heat exchanger (not mixing) and up to 95 per cent of the heat from the stale air is transferred to the fresh air being put into the habitable rooms of the home via ductwork and ceiling terminals. Good HRV systems will be Passivhaus certified, have an automatic summer bypass (no heat recovery in hot months), trap pollen and allergens down to 0.01 microns, and save about a third on heating bills. They should also have a controller ensuring the system is perfectly set up for your house and lifestyle with a 24/7 timer, temperature monitors, a boost function, memory cards, and cold weather, reduced supply-rate function.

However, even with the best HRV systems, there is still heat available to recycle. Heat pump ventilation (HPV) integrates a micro heat pump within the HRV unit to harness far more energy from the outgoing air. If you build a well- insulated and airtight home, you could take advantage of HPV and use it to provide a low energy heating system as well as ventilation.

They can recover 100 per cent of indoor heat and, for example, the HPV Series system enables users to obtain between 3.5 and 12 kW of heat energy, from only 1kW of power. This option also has three different supply temperature zones, as you may want different temperatures in your bedroom and living room, for instance. Another useful option is a heated ceiling terminal supplying quick-reacting top-up heating to a particularly cold room. The added bonus of HPV is that it can also provide cooling – useful on sticky summer nights.

That just leaves you to find a low energy domestic hot water source – the HPV Series includes a micro heat pump integral to a 300 litre water tank, so you get heat recovery ventilation, very energy efficient heating, cooling and hot water all in one system. This type of system will be seen in practice when the Build It Education House at Graven Hill in Bicester is finished. For more ‘petite’ homes, compact service units provide HPV with a smaller water tank integral to the unit.

It is important to ensure that the ‘veins’ of the system are correct – the ducting to each room. Rigid metal safe-seal ducting of 100-125 mm is best for airflows and hygiene (plastic isn’t naturally antibacterial) and is very robust on site. It also needs to be insulated correctly otherwise heat will be lost.

The principle behind heat pump ventilation and heat recovery ventilation is firmly grounded in the drive for more healthy, sustainable and convenient living. Perhaps all you need is the air that you breathe, to provide low energy heating, cooling, ventilation and hot water.

Clarissa Youden is associate director at Total Home Environment