Clarissa Youden, associate director at Total Home Environment, provides a guide to ventilating an energy-efficient, airtight home, going beyond MVHR with heat pump ventilation technology
People spend 70% of their time at home, meaning they breathe over 10,000 litres of air per day. It’s easy to assume that cracking open a window or two will keep the air inside a home pretty healthy. Sadly, that’s not always the case and a lot of heat (that’s cost a lot to produce), is lost in the process.
As homes are sealed and insulated more to keep the heat in and the cold out, the indoor air quality (IAQ) deteriorates. Unfortunately, lots of the items in a home leach out a cocktail of chemicals called VOCs (Volatile Organic Compounds) – things like carpets, curtains, sofas, laminates, cleaning detergents etc. Without controlled ventilation, most people will also live with high carbon dioxide (CO2) levels indoors, without ever thinking about it.
The air humans breathe out is about 100 times more concentrated in CO2 than in Earth’s atmosphere and studies have suggested that over-exposure can reduce cognitive and decision–making performance by 50% or more at common indoor levels. High CO2 levels during the night also result in restless sleep, headaches, a dry mouth and sensitive skin. But a solution is available
HRV & MVHR
Heat Recovery Ventilation (HRV) is a system that facilitates a ‘whole house’ air change every two hours, without losing heat. It works by taking stale, polluted, moisture-laden air from kitchens and bathrooms via ductwork and ceiling terminals and replacing it into living and bedrooms with fresh, filtered air from outside. Up to 95% of the outgoing air’s heat is recovered via a heat exchanger and transferred to the fresh incoming air. This heat recovery means less electricity, gas or oil is needed to heat your home. In summer, the heat exchanger within the unit can be bypassed, to enjoy cooler air overnight, where the humidity has been reduced. It has considerable benefits over other forms of ventilation like extractor fans and trickle vents, as well as passive stack, positive input or mechanical extract ventilation.
THE NEXT STEP
However, a further step in the sustainability journey can be taken with the Heat Pump Ventilation (HPV) approach, such as combining HRV with an integral heat pump. It requires no gas connection, expensive oil, pellet storage space, ground-drilling, radiators or underfloor heating. Heat is added to the fresh air supplied into habitable rooms of the house, via the ‘veins’ of the ventilation system – the ductwork, to provide highly energy efficient space heating. Multiple supply zones include an individually controlled supply duct that utilises the cooler air before the heat pump gets involved, so the master bedroom could benefit from a lower temperature for example.
The beauty of this system is that in the summer months the heat pump can reverse automatically, to provide cooling and reduce humidity, so that a 4-5°C temperature reduction could be experienced. Not only is this economic, but it is healthy, as it doesn’t recycle air like an air-conditioner.
Additionally, if a room-by-room heat-loss appraisal indicates more heat is required in certain rooms than others, but not enough to warrant the cost and hassle of a formal heating system, an HPV system can deliver. Supplementary heat can be added in innovative approaches so that there is more individual room temperature control with a quick response. This can be through the filtered air in each habitable room, where a standard ceiling terminal is replaced with a heated ceiling terminal that supplies extra, self-regulated heat. Alternatively, the HPV system can supervise a radiant heating panel, to bring a comfortable room temperature up to a ‘cosy’ one!
Despite this, it may still be handy to have heated towel radiators in bathrooms and WCs and perhaps a small wood burning stove or focal point fire in a sitting room.
Ventilation, space heating and cooling is all covered, without a large heat source, but how is hot water produced it there’s no boiler? An HPW air-to-water heat pump forms part of the system –
a 300L cylinder with an integrated heat pump – to provide all domestic hot water requirements energy efficiently. It can heat about 1,000L of water a day and has a secondary coil to provide heating for up to 20 m² of wet underfloor heating in a couple of bathrooms if required. This heating and ventilating system is designed to be over 600% efficient in comparison to a gas boiler.
HPV (and HPW) systems are suited to homes that are to be built or retrofit to Passivhaus/EnerPHit standards. However, the system may still be suitable if a home is well insulated and airtight with low U-values.
To ensure that heat pump ventilation is right for an occupier and their home, an installer should complete a room-by-room heat loss calculation. For this, floorplans, sections and elevations together with the U-values associated with the envelope of the home need to be supplied.
For townhouses and apartments a compact service unit could do everything that the HPV and HPW units do, but in a more compact form.
So while HRV/MVHR is great for ventilating a home without losing heat, is a ‘formal’ heating system required, with all the extra administration, installation time and trades on site, if a home is super-insulated and air-tight with a small overall heat loss? Or could heat pump ventilation be the whole house climate solution?