FAQs

There are several types of heat technologies on the market.  If you are near a large water source you can use a water to water heat pump.  This is regarded as the most efficient of all heat pumps.  However, it can be expensive to install and may need additional pumps to supply the water to the heat pump.

 

Geo thermal heat pumps take the stored heat from the ground either through a buried piping loop, or a borehole.  Both of these heat pump technologies can be expensive to install if you are unable to do the groundwork yourself.  If a ground loop is not installed correctly, this can cause permafrost.  Not all building sites are suitable for these technologies, due to either bedrock issues or space - but they are very efficient.

 

The air to water heat pump was chosen for the project as it demonstrates a virtual plug and use technology.  Very little site work is required other than a base for the unit.  Some form of shelter in an environment like Shetland is advisable.

 

An air to water heat pump extracts heat from the ambient air temperature and the heat exchangers remove the heat as this is passed through heat exchangers - the reverse of the refrigeration process.  An air to water heat pump can be sited in a small urban garden or even built into balconies in high rise structures, apartments for private developments or social housing units where a shared system would lead to energy efficiencies.

 

The project is also incorporating heat recovery.  This is a system that evacuates all the air within the house over a given period and passes the exhausted air through a filter - recovering 90 per cent of the heat.  The pre-heated air is again passed through a filter and is distributed through louves in the ceiling throughout the house.  This requires ducting to be installed but Villavent produce a retro fit product for existing housing.  This system has an override and, in summer, can switch automatically to air conditioning.

 

The 10 per cent heat loss is being recovered directly through the air to water heat pump through insulated ducting plugged into the inlet louvre of the heat pump.  We should be able to recover six per cent of this, leaving 4 per cent that is spilled.  This may increase to 8 to 9 per cent but, with any system like this, there are some inbuilt deficiencies.

 

A copper domestic water cyclinder is approximately twice the cost of the stainless steel unit that we are using.  This is fully insulated.  In Scotland, there are problems associated with mineral deposits in the water which can eat into copper tanks.  Some of this can be traced to poor fluxing of water pipes on installation.  The system we are using is unvented and is hooked up to an external inline water heater.

A 4,200 litre water battery is being used as the primary energy store for the under floor heating system.  This tank is constructed from GRP and is insulated with 200mm Celotex foam insulation.  This will only lose 0.5 of a degree over 100 hours if left unused.  To take advantage of this energy resource we are using a large Titanium coil to preheat the domestic hot water.  The coil is sited in the top part of the tank and takes advantage of heat convection.  The water main passes through the coil and is forced upstairs by gravity pressure into the insulated stainless steel tank.  When you turn on a hot water tap or shower, the inline water heater samples the incoming temperature 12 times a second and raises the water temperature on demand to the required preset temperature.  This system removes the need for a cold water header tank.

 

The entire structure of the house is timber and is clad with shiplapp timber from sustainable resources.  Apart from the block work for the foundation underbuild, the structure is made from stored carbon.  30 per cent of  the density of timber is stored carbon.  Aside from the energy, labour and transportation of the timber, no substantial energy has been used for the manufacture of building materials traditionally used in the construction of a conventional structure.

 

The complete house kit can be shipped to virtually any location and assembled by local labour, thus aiding local economies in terms of employment.  This is important in a fragile economy like Unst.

 

The Zero Carbon House is an off-the-shelf house supplied by Scotframe Timber Frame Engineering, reconfigured, and is available to anyone.  The UK is to be viewed as a maritime environment where lightweight structures with substantial insulation are easier and cheaper to heat than conventional heavy mass structures - where you have to heat the mass of the structure to gain any benefit from the heating source. 

 

The frame was erected by three men to water tight in 4.5 days in horrendous weather conditions.  A timber frame structure is relatively cheap to build, is quick to erect and ideal for severe climates like Shetland where you may only have a 'window of opportunity' to build.