OTHER VENTILATION TECHNOLOGIES – How to be positive and how to keep cool

POSITIVE INPUT VENTILATION We’ve now reached the fifth article in my mini-series about ventilation – I said at the outset that it was a complex subject. In the first article, we looked at the four main systems of ventilation given in the Building Regulations’ Approved Document F, ‘Means of Ventilation’. In passing, the document says that Positive Input Ventilation (PIV) may also be acceptable. The main attraction of this system must be its simplicity. It is basically a in the loft which blows air from the loft to the hallway or stairwell below. This increases slightly the air pressure in the whole house, and so air in all the rooms is gradually expelled through the fabric of the building. Heat is saved as the result of taking in fresh air from the loft, rather than from outside. Air in the loft is said to be about 3ºC warmer on average, due to solar warming of the roof and the conduction of heat through the loft insulation. (This latter effect must be smaller, nowadays, because of the greater thickness of loft insulation being used.). A large filter keeps out pollen, dust, etc. PIV systems were originally developed in Britain in the 1970’s to deal with condensation problems in old houses. But they are also very relevant to new build today. A BRE Information Paper says that a PIV system may result in lower energy use than a conventional extract system. (See Further Info.) If PIV is to be used in a timber frame house, make doubly sure that the vapour control membrane of the walls is intact. If there are holes through which moist air would be forced, condensation could occur in the framework, with the risk of rot. Nuaire’s Drimaster units have an Agrément certificate whereby extract fans and trickle vents are not generally required in order to meet the building regulations. But in a wet room without direct access to the hallway (eg, an ensuite), an extract fan or trickle vent is required. (Personally, I’d be inclined to fit trickle vents in all wet rooms, even though not strictly required.) For fast extraction in a kitchen – just open the window and the positive pressure will expel the air. A PIV system can be safely used with flued stoves, eg, an Aga. The positive pressure (about 2 Pascal) assists the escape of combustion gases up the . Positive Input Ventilation is probably the cheapest and easiest to install of all the ventilation options. Trickle vents, extract fans, and super airtightness are unnecessary, or even undesirable. These systems are modestly priced and very cheap to operate. For example, a lowish setting on the Drimaster 365 unit uses only 3 watts for an airflow of 20 litres/sec. (Compare this airflow with the CIBSE recommendation of 8 litres/sec per person, or the SAP requirement of 4 litres/sec for the house and 4 litres/sec for each occupant.)

Nuaire’s Sunwarm System The Sunwarm system combines Positive Input Ventilation with a couple of solar panels, but solar panels with a difference. Air flows through them, not water, and so the problem of water freezing in solar panels is neatly avoided. In wintry conditions, the tempered air is used for ventilation and blown into the house. In summery conditions, the hot air is passed through an air-to-water . Then the warmed water is pumped to a second coil at the bottom of the hot water cylinder, as in conventional solar water heating.

OTHER VENTILATION TECHNOLOGIES 1 MAY 2007. The greatest amount of heat is captured in the summer and used for water heating, so this extension of PIV is primarily a means of harvesting solar energy for hot water. The tempering of the supply air on a sunny winter’s day is a secondary benefit. But there is a further benefit. In summertime, the system can be used to cool the house over-night – the panels cool the air which is blown into the house. Nuaire make some impressive claims for Sunwarm. In a typical situation, the system requires only 200 kWh of electricity annually, and saves about 4,000 kWh of gas or oil energy. Nuaire claim that the Sunwarm system can save twice as much heat as a more orthodox solar water . In fact, they might be understating their case. In ‘Tapping the Sun’, a booklet published by the Centre for Alternative Technology, the typical annual saving resulting from a conventional solar system is given as 1,200 kWh. Twice this heat saving is 2,400 kWh, well below the 4,000 kWh saving claimed by Nuaire. The Sunwarm Plus version combines Sunwarm panels with an HRV system, instead of a PIV system.

SolarVenti panels In the March issue of the magazine, the launch of SolarVenti into the UK was announced. The panels give solar-powered Positive Input Ventilation with pre-warmed air. No mains electricity is used. These panels are intended primarily for the winter ventilation of intermittently used spaces such as summer houses, cellars, boats, etc, but they may be of use to some selfbuilders. One model even incorporates solar water heating, somewhat akin to the Sunwarm system.

KEEPING COOL IN SUMMERTIME Approved Document L1A, ‘Conservation of fuel and power in new dwellings’, sets out five criteria that have to be met. Criterion 3 states: 'The dwelling has appropriate passive control measures to limit the effect of solar gains on indoor temperature in summer.' This can be achieved by “an appropriate combination of window size and orientation, solar protection through shading and other solar control measures, ventilation (day and night) and high thermal capacity”. That last phrase implies that masonry construction is better at limiting summer overheating than timber frame. The document goes on to say that “the aim is to counter excessive internal temperature rise in summer to reduce or eliminate the need for air conditioners”. In , air is cooled by a , a process which many people regard as wasting energy. With our climate getting warmer, the authorities are clearly determined to head off any movement towards domestic air conditioning – which would, of course, only increase carbon emissions and global warming. What is more acceptable is a whole house ventilation system using night-time air to cool the house. The Sunwarm panels mentioned above are very effective in this respect. Most HRV systems have a summer bypass so that the incoming air bypasses the heat exchanger – the incoming air stays cool, and is not warmed up by the extracted air. In my own house, I find that summer cooling is easily accomplished by opening some windows in the early morning. Under the , cool air flows through the house, and after half an hour the cooled house is ready for another hot day. The

OTHER VENTILATION TECHNOLOGIES 2 MAY 2007. walls have good thermal capacity because they have been built with standard aerated blocks. (Extra light, aerated blocks would have given less thermal capacity, albeit better insulation. Solid concrete blocks would have given much more thermal capacity, though less insulation.) Furthermore, the plaster undercoat is a sand/cement mix, rather than gypsum browning – again, to give more thermal capacity.

Are you a techie or a greenie? In the winter edition of Building for a Future, Dave Elliot of the Open University wrote an article about the division of opinion between ‘techies’ and ‘greenies’. “Techies say that hardware can cut (carbon) emissions, greenies say that we have to live differently.” As far as the issue of summer cooling is concerned, the greenies surely win the argument – simply open the windows rather than look for some super-efficient form of air conditioning. But the solutions are not always so clear-cut. Both techies and greenies will find much to interest them in Building for a Future. You can either subscribe directly to this excellent quarterly magazine, or else receive it as one of the benefits of a subscription to the Association for Environment Conscious Builders. (See Further Info.)

HRV with heat pump In my article on Ventilation and Heat Recovery in the March issue, I said that extracting extra heat from the exhaust air stream by the use of a heat pump is a good concept, but that such systems are hardly available in the UK. A company called Total Home Environment have since told me that they now distribute Genvex systems. Genvex are a highly regarded Danish company, and details of their products are available on the Total Home Environment website. (See Further Info.) The effect of the heat pump is remarkable. With an outside temperature of 2ºC, fresh air can be supplied to the rooms at 38ºC. In a super-insulated house, this sort of system could even be the main heating system. A Coefficient of Performance of 5 is claimed by Genvex. Using warm air for heating was tried in the UK in the Seventies, but not well received. With a super-insulated house, the heating demand is much smaller, and this form of heating may be more acceptable. (Heating with warm air is widely used in Canada, for example.) An Irish company, Low Energy, have their Airexe system distributed in the UK. This too combines HRV with a heat pump. Their figures show a Coefficient of Performance of about 3.5, a more modest but probably more realistic figure than the Genvex figure. By reversing the operation of a heat pump, summer cooling can be obtained. In the techie-greenie spectrum, HRV systems with heat pumps must surely be at the techie end of the spectrum. If you want an HRV system without a heat pump, the aluminium counterflow heat exchangers used in other Genvex systems have an amazing 95% efficiency in optimum conditions – and about 88% in practical use. By the way, Genvex also produce Vanvex, a water store incorporating an air-to-water heat pump. Its Coefficient of Performance is more than 3, so this could be a good option for producing hot water in homes where mains gas is unavailable.

OTHER VENTILATION TECHNOLOGIES 3 MAY 2007. FURTHER INFO: Positive input ventilation in dwellings BRE Information Paper IP 12/00, (£9). www.brebookshop.com. Building for a Future Bi-monthly magazine (£20 pa). www.newbuilder.co.uk. Association for Environment Conscious Building (AECB) Subscription is £35 pa, and includes the above magazine. www.aecb.net. Nuaire Home Ventilation Ltd Both simple and innovative PIV systems (including Sunwarm). www.nuaireforhomes.co.uk www.sunwarm.com. Energy and Environment Research Unit Part of the Open University. Their website contains extracts from ‘Renew’, the bi-monthly journal of NATTA, the 'Network for Alternative Technology and Technology Assessment'. eeru.open.ac.uk. SolarVenti UK solarventi.co.uk. Genvex This Swiss-owned, Danish company has a new distributor in the UK, Total Home Environment Ltd. www.totalhome.co.uk. Airexe This is an Irish HRV system with a heat pump. www.lowenergysolutions.co.uk. The Irish company also makes air-to-water heat pumps. See: www.lowenergy.ie.

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© Copyright article by Robert Matthews in SelfBuild & Design magazine,May, 2007.

OTHER VENTILATION TECHNOLOGIES 4 MAY 2007.