A passively heated house is just warm or cool and even if you know why, you are not conscious of the temperature changes. A properly managed/built home is comfortable and fresh and cheap to run.

Either you have a home that needs cooling in the day or heating for the night, or as the seasons change, your home may need to retain heat all day. So you need to have a range of features built into your home that store this heat for use at night and allow you to release it through vents (roof vents are ideal) when it becomes too hot. Airflow, or lack of it, will govern how you control the passive heat that collects in your home.

Cooling your home by venting heat off is pretty easy as we all know that heat rises. A roof mounted window/vent is probably a good start and you may be able to provide venting from room to room by hatches or opening windows at a high level. Venting permits the air to flow which encourages fresh air to enter rooms and stop stuffiness. The other main way to promote cooling is to prevent the heat coming in by providing shading either by fitting sunscreens on the outside of the house or blinds on the inside. But it is not entirely that simple in all cases.

Introducing heat into your home once the sun has gone down involves a bit more cleverness than cooling it in the heat of the day. Firstly you have to collect the heat and to retain it and then to make sure the heat is not wasted. The roof vents you may have employed in the summer can now be closed, but only because they are double glazed will they be effective. Blinds will prevent heat loss and having double glazing fitted throughout is essential to insulate your home against heat loss. A single glazed window is like an open door as far as heat retention goes.

To illustrate passive solar heating, it's probably best if I mention the 70's house we have in the north of New Zealand. It is a terrible example as it doesn't work. The upstairs or living area is timber with acres of north facing windows and it does get warm in the day. In fairness the back of the house is less windowed and is cool in the summer and can be well vented although not through the roof.

The downstairs flat is a blockwork structure which is a great idea for retaining the heat of the sun and letting it off slowly but the verandah from upstairs is so big that the really needed winter sun is shaded from the walls except in the morning or evening when there is little power from the sun. Our house seems geared for the summer day and for cooling only, because there is plenty of ventilation (there is no roof vent but there are lots of windows opposite each other) and shading. Which is typical of NZ houses. Ventilation and shading is all that should be required for cooling and the important things like heat retention and saving are blithely ignored. I can assure you NZ is not or probably never roasting hot. You can ski here in the winter.

The reason why I know our house retains very little heat is because as soon as the sun goes down the inside is always the same temperature as the outside with all the windows closed. There is no insulation in the roof whatsoever and whilst the timber walls do have insulation within them as per its manufacture, technology has improved since the 70's and timber walls are poor insulators anyway.

The windows are also single glazed and whilst they may be super at collecting heat they lose heat just as quick. Drawing the heavy curtains seems to delay the cold creeping in but not for long. Other than the downstairs walls being blockwork, there is also no medium to retain the heat of the day. Thank God for the timber fire in the main room but the rest of the house can get cold which personally I don't mind.

So, by having roof vents fitted, double glazing and roof insulation, things would be improved and value could be put on our home but probably not by the amount spent. Grants may help and in the UK these are available for loft insulation. A friend has a double glazed velux window fitted into the roof of his extension and it's the best room in the house winter or summer.

To further improve the heat capacity of this house you would need to use materials and methods that retain heat well. This is something that is not usually done as an after-thought but in the very conception of its design. To understand the ways heat can be retained it is best seeing the web pages I have recommended. They seem to say it perfectly.

www.greenhouse.gov.au
www.jc-solarhomes.com
www.soundhome.com
www.azsolarcenter.com
www.earthshelters.com

Active Solar Heating is different from Passive Solar Heating in that you are not exposed to the variables of sunlight, airflow and materials within your home reflecting or absorbing heat. Certainly some elements of Passive Heating can be achieved pretty easily but it is probably unlikely that you can quantify it. You cannot buy a Passive Solar Heater. It’s just that some features of your home will contribute to Passive Solar Heating. You can however, buy an Active Solar Heater and you can say what it will do for you for sure.

Some active solar heaters simply collect hot air from a large black metal plate that sits in the sunlight next to an air intake on your house. See www.oikos.com. This system can be further improved if the hot air you collect in a greenhouse or patio area of your home is used with a heat pump to transmit heat into your house. Think of the heat pump as a fridge in reverse. (See heat pumps in the next section for a clearer picture of what heat pumps do). It takes the hot air from the outside and makes it hotter and fans then push the air round to where you need it. Generally though, using air heated by a metal plate is a bit dated as air con units do more or less the same job and come self-contained.

http://jc-solarhomes.com has some great designs for homes that take advantage of naturally available heat.

Mainly though, Active Solar Heating is an unnecessarily vague description for a solar water heater and in my recent conversations to a friend about his newly built house and his environmental solutions he has fitted a solar water heater because they are 'awesome' and 'the last house had one and it saved us a fortune'. I looked in the phone book to find signs of suppliers of this new technology and the brave people that had embraced it without question of its ability. I was naturally disappointed to find three pages of companies that could supply and fit them and then realised that it is not actually cutting edge technology any more. Well it was to me.

As you can imagine with such a well developed piece of kit as a solar water heater there are many variations and models and sorry I cannot tell you which ones are the best. Hopefully 25 years of development will mean that whatever the purchase you make, it will do what it’s supposed to do for many trouble-free years and put value on your house at the same time.

Solar water heaters are basically roof mounted radiators. Work on 1m x 1m per person. Cold water that would normally go into your hot water tank and be heated there is, instead, pumped (this can be a solar pump) into a panel on the roof where it passes slowly through a series of tubes. It leaves the roof panel much hotter than when it went in and when it returns to the hot water tank, only a small amount of power is needed to raise the temperature of the water to the desired heat. There are options for storing the water on the roof to further heat it, or in cold climbs the sun is used to heat antifreeze which in turn heats the water for your home. It’s all really very effective and is controlled by electronic things that keep the system operational and delivering hot water to your hot water tank.

However, it is most common to find that people cannot rely solely on a solar water heater for their hot water needs. In a family home a huge amount of hot water is consumed. The reason for having the solar heater is so that your electric water heater does not have to work as hard. Typically, electricity bills for hot water heating are reduced by about half.

If a solar water heater is included into your alternative energy portfolio, you are approaching a possible solution for providing heating for your home whilst your solar panels and wind generator provide power for your appliances and one day charge your car.

Further information is available at www.apricus-solar.com and for suppliers and products see our Products section.

A Heat Pump is a compressor. The compressor works with a material called a refridgerant by compressing it and making it become hot and liquid, or reducing its pressure and turning it into gas and making it cold. The refridgerant is a special material designed to change state from gas to liquid as the compressor is brought into use. Your heat pump or air con unit has a button you can press that essentially selects the temperature you want and the compressor turns on and either makes the refridgerant into a gas for cooling or a liquid for heating.

A fridge is a heat pump. It effectively pumps a very cold low pressure refridgerant around the inside of the fridge and all the hot air is gradually removed. The noise you hear is the compressor making the refridgerant cold by keeping it gaseous and at a very low pressure. An air conditioning unit is a fridge with a fan on it and the reason why they are expensive to run is that they use the cold in the air outside to make the air inside even colder. On hot days there is still an amount of cold in the air but not much. They should be put in the coldest location possible, preferably in the shade.

The concept of using pressure to govern temperature is difficult to grasp, but I imagine that heat pumps or air con units operate like a magnifying glass with the sun on one side and intense heat on the other or a cool wind on one side and an icy chill on the other. The heat is made hotter and the cold more intense. The energy saving part of all of this is that the heat pump magnifies this hot or cold air simply by the use of only a small amount of power to operate the compressor. To make that amount of heat directly with an electric fire would take 3 to 4 times more energy. Typically, cooling air uses more energy than heating it.

I remember an example of a farmer heating his home from the milking shed. By using the hot environment of the milking shed, the compressor worked very little to heat up the refridgerant which was pumped down the pipes to his house that heated the radiators. Using this source of hot air from the cows meant that the compressor did not have to work as hard as trying to extract heat from the normal outdoors.

In the colder regions of the US they combine heat pumps with the heat of the ground to heat their homes and this type of system is well developed and considered normal to home owners. Below 3m (10ft), the ground is a more or less constant temperature all year round, so as the air temperature outside approaches freezing, this heat source is utilized. Remember though that the energy consumed in gaining this heat is the small amount used to operate the pump.

All Heat Pumps including Geothermal are explained at:

www.flex.net

Heat pumps/Air conditioners are available in any phone book. You can also see what is available in Products.

Air conditioners are typically associated with cooling although they can also be used to provide warm air. If warm air is needed much more, then the heat pump should ideally be exposed to a source of heat. The theory is that since ground water maintains a temperature of around 10 degrees C no matter what time of year it is, this heat/cold source can be used to heat your home in the winter and cool it in summer. The geothermal heat pump pumps water into the ground via a series of pipes drilled into the ground and then looped back to your home. Rather than using air as the source of temperature let’s say, the geothermal system relies on this water.

It may sound like a big job but it is not and can be done at any time. Either you do it during the construction of your home or you can let the mini tunneling machine push the pipes into the ground around your garden. Typically it takes around a day to do the piping but if your house is built on pure rock it might become impossible to do due to the expense. Many parts of the US and Canada consider this sort of home heating to be normal but not so in Europe or anywhere else just yet.

Typically, heating bills (this will not heat your water, just room heating and cooling) will be reduced by up to 60% compared to normal home heating, and it is an asset that will add value to your home.

Companies that can do this are featured in Products.

Biomass is wood and whilst wood will burn and give off carbon dioxide, there is the idea that there is a lot of forestry wood waste that would rot anyway and give off methane, which is a worse greenhouse gas. It’s true that there appears to be a lot of waste wood in some nations, and historically and currently, wood has been/is the prime mover in nearly all parts of the world.

Introducing efficient wood burners is total common sense in the countries that have all the waste and spare wood. The boilers and stoves available are very efficient and as you would imagine with a boiler, it means you can sit next to your roaring fire and at the same time heat the water that is plumbed into it.

However, encouraging the use of biomass (usually for cooking) in developing nations where wood is neither spare nor a waste product, is essentially damaging the environment. Large areas of North West India have been deforested simply to satisfy the demands of the local people for cooking. Even today, rural peoples still carry machetes around and all the lowest branches of the trees are lopped off. There is a range of cookers available in third world countries that are less harmful to the environment.

In the first world, the product range varies from just the simple wood burner to the simple pellet burner which is more efficient, and then there are burners for cooking on and there are wood burning boilers that are room and water heaters together. They all come in a variety of colours and designs and even though they may not be supremely environmental I like them. I think you have to convince yourself that you are indeed saving the world from the ravages of methane to realise the fullest satisfaction of a wood burner. Go and buy a decent saw and an axe and sort out all the fallen/rotting trees in your neighbourhood and have a look in the Products section.

Where there is a copious supply of material, industrial applications can be established, and rather than just being used for water and room heating boilers, wood can be used in Combined Heat and Power Systems to extract the most out of wood fuel. In this case, the heat energy is used to heat water, air for room heating, and to generate steam and ultimately electricity.

A family car is a great example for Combined Heat and Power. Its engine uses petrol to drive the wheels round and at the same time it makes electricity for the battery and provides hot air for the occupants. If you decided not to drive it anymore, you could raise it on blocks and use the wheels to drive a generator round. With the engine running you would also heat up water and if you turned on the fan, hot air would emerge. A CHP system is basically the same as this but of course a CHP plant is devoted to using all its effort to make things go round and its by-product, heat, is captured in the air and water system surrounding the motor used for power generation.

CHP systems can be tailor made for producing power, hot water and hot air for your home, office and industry. No source of heat or power is wasted. Institutions such as museums and hospitals are choosing to use biomass (waste wood) where available, otherwise gas turbines are the primary source of power. In Japan, the refridgerator sized gas powered CHP systems are very popular in new homes and they combine water boiling and power generation nicely. It used to be perceived that these were noisy but not anymore. The industry surrounding this technology has seized upon silence to promote the invisibility of energy and heat generation which it now calls cogeneration.

See: www.climate-energy.com/faq.asp for these Micro-CHP applications.

CHP is not really an alternative energy, but a system that allows us to utilize our resources more effectively. The transition to full blown alternative energies will take at least a generation and using CHP will no doubt endure as the fuels used in CHP will be available for a long time. It is possible to convert existing boilers and generation systems to CHP and most large establishments like hospitals and universities which already have a boiler, are well placed to benefit from a conversion.

Gain a better idea at:

www.chpa.co.uk - Combined Heat and Power Association site in the UK
www.epa.gov - Similar for the US

See our Products page for further details.