I touched on DVS systems in my last blog and I will go a bit further today.
There are two systems that can take warm dry air from the roof space and pass into the home via ceiling outlets. The generic names are Domestic Ventilation Systems (DVS) or Home Ventilation (HRV). Do not get confused though with Heat Recovery Ventilators (HRV) which take warm moist air from the house and via a heat exchanger replace it with dry slightly less warm dry filtered outside air.
I will from now on call the DVS and home ventilation systems, which are the basically same product, the general name of DVS. These are also known as Positive Pressure Ventilation (PPV).
During a sunny winter’s day the roof cavity can get hot with the sun shining down on it. Clay tiles do not make the roof cavity hotter for longer than a metal clad roof and take longer to warm up.
What a very basic DVS system does is blow this warmed dry air via a filter into the house. This dry air pushes out, via gaps in windows and doors, the moist air caused by breathing, washing, cooking, etc.. Buying a dehumidifier to cure a moisture problem is useless as you are only getting rid of the symptoms of the problem not the cause of it. They have to be constantly emptied and are only reducing moisture in the area they are situated in. They also cost more to run than a basic DVS system, which is just a fan. Some people have found that they have had a reduction in their heating bills after fitting a DVS system. This is because it can warm up a home for the cost of just a fan running and it is easier to heat up dry air than moist air, as there are less water molecules in the air to warm up. Other benefits air that the air is filtered and can reduce asthma and allergy problems. If there is positive pressure inside a house there is less chance of pollens coming in. The most obvious addition to the system is to have a heater that takes the chill off as the air in the attic space cools down at night or on none sunny days. In most systems the heater just makes the air from the attic the same as the room temperature at best. With the system from Moisture Master you can have a 2kw heater, which on the highest setting actually blows hot air, but not enough to heat a house.
If you have got a pellet or log fire there is normally an option to take very warm air from near the fire and pump it around the rest of the house. This is a very low cost option as the whole house can be warmed up at the cost of running a fan. Obviously there is a thermostat that switches between the attic air and the ‘fire’ air depending on temperature. There is also a system that moves air from the fire area to other rooms. This only really works when the fire is going and for the price you would be better off buying a DVS system which can supply dry air all year round.
The last option is the summer option. This takes cool air from the South side of the house and blows it into the house. You could go out on a cold morning and shut all doors and windows tight and later the weather changes and your house starts to become hot and stuffy. With the summer option as the house gets too hot cool air is blown in and reduces the heat almost as if you had a window open.
The shape and size of your home and your family’s needs dictates how many outlets you have. As I have a long house I chose to have two outlets in the bedrooms furthest from the heat pump and one in the lounge at the other end. It is important to remember that these systems can give benefits even when there are no other heating or cooling systems in use. So if you are in Australia for 2 weeks in the winter you can come home to a freezing house. All the static air in cupboards and behind furniture, especially on the south side of the house, has come down in temperature to near the outside temperature. This cold air on your return can take several days to warm up. With a DVS system running, warm air on sunny days has been pumped all round the house and kept the overall temperature higher than it would have been. So do not rule out having an outlet in the area near a heat pump as you may not have to turn the heat pump on depending on how big your heating element is.
With any system that draws fresh air from the roof cavity or outside, which is then passed into the home, there could be a smell in winter, if you live in an area with lots of log fires. If you step outside your door on a winters night and you catch the sweetish aroma of smoke, that smell will probably be drawn into your home.
I have the Moisture Master system which has an automatic mode, but allows you to control the heater temperature and fan speed. So on a cold day I can turn the fan down to half setting and turn the heater up to the highest setting and nice warm air flows into the house. You must not have the fan setting more than the heat setting otherwise the air will not have had chance to warm up as it passes over the heating element. At night we turn the heating down to half and the fan to the quarter setting just so that the chill is taken off the night air. On hot days we have the fan on full so that cool air is blown in whether we are at home or not. On several days last year we had the system set to auto and with the heater on. Later during the day the sun came out really warmed the house up and the system swapped over to cooling.
If you suffer from ‘crying’ windows, thinking of buying a dehumidifier, constant cold hands even when the heat pump is on or damp and mould, a DVS system could be for you. There are various options so get various quotes and go for the option that suits you best. Money should not come into the equation as they could save you money and fitting extras later could be a lot more expensive. I saw a lovely expensive house with varnished wood everywhere; because of crying windows a very large internal wooden window sill had rotted. To replace that sill will cost more than a basic DVS system. Talk to people that have one and see what they reckon about it.
Remember with one of these installed can make your house more resalable.