Low Energy Technology
Heat Recovery Ventilation (HRV)
Constructing an air-tight house means an HRV unit becomes an essential component to provide constant fresh air to the living space.
HRV units work by having ducts installed throughout the building, going from the HRV unit to most rooms, with two ducts going to outside from the unit. The runs of these ducts are best designed by us at the frame design stage, so that holes can be pre-cut within the timber frame ready for the ducts to be pushed through – simplifying the work on site greatly.
HRV units work by taking air from the stale air locations within the house – kitchens and bathrooms, then extracting this air to outside via a heat exchanger, so that fresh air is preheated by this air leaving the building (at a 92% efficiency for the PAUL system). Fresh, warmed air is then delivered into the living areas – lounge and bedrooms via a vent from outside. This system provides a constant exchange of air within the building, without loosing the heat contained in that air. The process is very subtle, with air gently being pumped round and takes time to get used to with most people being used to the sledge hammer approach of oil heating where masses of heat are put into a space, the majority of which is quickly lost through the building structure.
HRV units also contain filters to avoid dust and particles entering the duct system so the air feels very fresh. These filters need to be changed on a 6 month basis to ensure the continued efficient running of the system.
As an option, the units can also contain a heater to provide hot air into the building during the very cold winter months. This heater can be electric, or a water based radiator much like a car radiator which can be fed from the building’s hot tank. Alternatively heat can be delivered into the building (if needed) from a room sealed wood stove or similar.
To achieve the passivhaus standard the HRV unit needs be extremely efficient, a recommended product being the PAUL HRV from the Green Building Store. This achieves a 92% efficiency, which means little heat (8%) is lost during the air exchange process. If an inefficient unit is used, then much heat will be lost (similar to leaving a window open) negating the advantage of building an air-tight house.
Installation notes
It is vital the ductwork is installed correctly and the vents are commissioned. All duct work being metal needs to be fully insulated along the complete run, otherwise most heat will be lost through the duct walls, rather than coming out of the vent. It is also important to have vents above door openings, to allow air to circulate between rooms.
Log Stoves - close to carbon neutral heating
We no longer need to heat a new house with a standard fossil fuel based central heating system – our houses have a minimal heating demand due to their super insulation and air tight nature. The small amount of heating required can be supplied via a heater in the HRV unit, or more often clients opt for a room sealed wood stove. Wood stove’s provide an excellent centre piece to a lounge, are fuelled by a local product – rather than using oil extracted from abroad, refined and transported to your home to be burnt for heat.
Wood is also a near on carbon neutral source of heat - the tree sequesters carbon from the atmosphere during its life time, which is then released again when the logs are burnt ? so there is no net change in atmospheric carbon unlike when fossil fuels are burnt.
Using wood fuel also means your money goes into your local wood fuel economy rather than leaving the country – and of course is near on a carbon neutral source of heat.
For woFor wood stoves in an air-tight house it is vital an air sealed unit is installed – otherwise complications will arise with the HRV unit.
Our Touchwood House project features a log stove as the main heat source, the same as the Jotel stove above. Log stoves now have a modern look and are impressive lounge centrepieces.
Installation notes
It is vital room sealed stoves are used in an air tight house – rather than conventional types that combust the air within the room
Log Boilers
Log boilers have a water jacket around the firebox which heats the water to then be stored in the thermal store. These types of boilers can be very efficient with most of the heat produced going into the water (rather than into the room), which can then be used for domestic hot water, showering or underfloor heating systems. If this system also has a circuit going from the hot tank to a large solar panel then all heat / hot water in the building can be delivered in a near carbon neutral manner, with the solar providing all the heat in the summer and the logs in the winter. The thermal store can also have an electric emersion heater installed for those times when you need hot water quickly.
Our recent cottage renovation project features this system and works very well.
Wood Pellet Boiler
Wood pellets are around 10mm long and made from compressed sawdust, looking a bit like pig food. Being small this fuel flows like a liquid so the boiler can be computer controlled with an automatic auger feed, operating much like a conventional gas/oil boiler.
Pellet boilers are linked directly to a thermal store, automatically heating the water when it drops below a preset temperature. These thermal stores can also work in conjunction with a large solar panel and so provide continuous hot water to the house during the year with the owner being unaware if the heat is derived from the solar array in the summer or wood pellets in the winter months.
Typically pellets are fed by auger to the boiler from a large buffer store which can be filled by hand from 10kg bags. Once filled the system can be left alone, with the boiler automatically coming on when the temperature in the thermal store drops below the minimum.
Our Portland Place project features a large Ökofen wood pellet boiler supplying both 3 bedroom properties which works in conjunction with the large solar panel.
Photovoltaic (PV) Panels
With the new government feed in tariff scheme PV panels make good financial sense with payback periods of around 8 years followed by an annual income from the system. PV systems can even be installed free of charge now, with the installer keeping the annual re-fit payment and the client receiving free electricity during the day.
Solar Water Heating
Heating your water directly from the sun is a simple but reliable technology; most Touchwood homes feature solar panels. To make effective use of the heat produced it is essential a large thermal store is installed (rather than a hot tank), the system will then be capable of providing free continuous hot water for around 7 months of the year - and will also pre-charge the thermal store during spring / autumn so reducing the run time of your winter hot water supply system.
Installation notes
Be aware of poorly installed and designed systems where a small solar panel is connected to a small hot tank so providing an inadequate volume of hot water to be of practical use. Or one where poor controls result in the immersion heater filling the hot tank with hot water in the morning, so making the solar panel redundant during the sunny time of the day – the hot tank needs to contain cold water in the morning so the solar panel can heat it during the day.
Ideally the tank temperature needs to be displayed in a visible location such as in the kitchen. Then if there has been a prolonged period of no sun, you will know when and if you need to use an alternative method such as immersion heater or boiler. Solar panels are not really plug in and forget technology, the user needs to have an interest in them. Personally my tank temperature is displayed in the lounge, with a button nearby to turn the immersion heater on. I tend to use the immersion heater around 10 times a year (10 hours in total) the rest of my hot water is supplied by solar for 8 months, and a wood boiler in the winter.
Many solar panels are installed incorrectly, resulting in them rarely producing any heat - a great shame since this is a brilliant CO2 saving technology.
Thermal Store
To make effective use of solar panels it is vital a large thermal store is used, otherwise the panels will not work effectively – most plumbers we have spoken to fudge this issue. On a conventional hot tank, when a hot tap is turned on the water in the tank directly goes from the tank to the tap. When some thought is applied, this is clearly a very poor way of using the heat:- If thIf the tank contains very hot water, the hot taps will supply this very hot water which will then require cold to be added at the point of use – otherwise users will be scalded in showers etc. This is a dire waste of the heat energy stored in the water.
- Once hot water leaves the tank, the header tank will supply new cold water to the tank which will further waste energy by bringing down the tank temperature.
- For hard water areas the constant replacement and subsequent heating of the water means lime is constantly being deposited in the tank – so the tank will only have a short lifespan.
- Hot tanks are typically quite small so do not store much heat.
- If water is stored in the tank for a long period at medium grade temperature there is a danger of water born bacteria breeding, meaning water from the hot taps should not be drunk
The alternative thermal store is filled with water (plus chemicals) upon install. This water then never leaves the tank. Instead when a hot tap is turned on, cold water is fed directly from the cold main through a loop (coil) within the tank. When this cold passes through it picks up heat via conduction within the pipe then arrives at the tap. The speed of this flow is adjusted so that if (for example) the tank is full of 80 degree water, the hot supply flows through quickly and so is heated to around 45 degrees. This is then a good temperature to shower in, without the need to add cold water which would waste all that heat.
Taking heat off at the temperature you require is massively more efficient. If say, the supply cold main is at 10 degrees, we are taking off 35 degrees from the tank, leaving 45 degrees in there. For the hot tank scenario we would be taking water off at 80 degrees and replacing it with 10 degree cold water – this is clearly a very inefficient use of your hot water store.
Warmcel Insulation
Warmcel is a UK produced insulation product, the main component being treated recycled newspaper. To install Warmcel we pump it into the wall cavity under high pressure – this installation method being a major advantage of the product since it ensures the product fills the cavity completely.
This offers excellent insulation, environmental performance and near zero embodied energy. Warmcel also provides a great deal of thermal mass to the structure, stabilising the internal temperature.
Wind Turbines
We have been involved with wind turbines of various sizes and have actual production figures to show which sizes are worth installing and which are too small. It is now widely acknowledged that roof mounted varieties are too small to be worth using.
The location of a turbine is critical to the machine producing a significant amount of power. Touchwood have been providing wind turbine site surveys for Segen Limited, and so we are well qualified to advise on whether your situation is suitable for this technology.
With the feed-in tariff now in place, the turbines below are eligible for payment of 26.7p /kWh produced, resulting in a payback period of around 7 years – making these turbines economically impressive for a site with a good wind resource.
The Gaia 11
The Gaia 11kW turbine has a very large blade with
a diameter of some 13m. This provides excellent performance at the low wind speed
sites typical in lowland areas of the UK.
With 150 wind turbines already installed, Gaia-Wind has more than 1,000 years of operational turbine experience.
The Gaia turbine is technologically a large turbine scaled down, rather than a simplistic small turbine scaled up. This means the machine has the advanced control software installed normally associated with large wind farms which maximises energy production through constantly measuring wind speed and direction. The machine can also be monitored online to see how much energy is being produced.
Technical spec:
| Rating: | 11kW |
| Blades: | 2 |
| Diameter: | 13 metres |
| Tower Height: | 18metres |
| Grid Connection: | 3 phase only |
| Foundations: | 5m x 5m x 400mm Concrete |
Full Product Specification
| AMWS | Annual MWh | Daily KWh |
| 4 | 18.9 | 51 |
| 4.5 | 25.1 | 68 |
| 5 | 31.3 | 85 |
| 5.5 | 37 | 101 |
| 6 | 42.4 | 116 |
| 6.5 | 47 | 128 |
| 7 | 51.2 | <>140 |
The Iskra 5 kW Wind Turbine
Working with Segen we are now able to supply the 5kW Iskra AT5-1 Wind Turbine. This machine is large enough to produce around 8,000kWh/year on a reasonable site in the South of the UK.
Touchwood were so impressed by the Iskra we have our own on a site in Hertfordshire which was featured on the Grand Design Live TV show.
Technical spec:
- Rated Power :5kW (at 10 m/s)
- Max Power: 5kW
- Blade Diameter : 5.4m
- Tower Height : 12m monopole
- Rotor Speed: 200rpm
- >Start wind Speed: 3 m/s
Full Product Specification
| AMWS | Annual MWh | Daily kWh |
| 4 | 5.0 | 13.0 |
| 5 | 8.7 | 23.9 |
| 6 | 13.1 | 35.9 |
| 7 | 17.1 | 46.8 |
| 8 | 20.2 | 55.3 |
| 9 | 22.2 | 60.8 |
Note:Note: the annual electricity consumption of a medium sized house is 4 to 6 mWh. This is equivalent to a daily consumption of 11 to 16 kWh.
AMWS is the Annual Mean Wind Speed in m/s, a rough idea of the AMWS for your area can be found on the BWEA website. Typically a good site in the South East has wind speeds of around 5.0m/s at hub height.
Heat Pumps
In the UK with our mild, wet winters heat pumps have been shown to have a COP of 2.3 to 2.5. i.e for each 1kW of electricity put in, 2.3kW to 2.5kW of heat is returned. This has to be taken in context – currently roughly 70% of electricity in the UK is produced from fossil fuels with an average efficiency of 30% (i.e 30% of the energy in the fossil fuel creates electricity, the rest being lost in the form of heat). Due to the processes in involved here, fossil fuel -> electricity - > heat pump -> heat, there is a lot of efficiency losses making heat pumps powered by fossil fuel plant a debatable option. As the grid becomes powered by more renewable electricity though, heat pumps make a lot of sense so if other options such as solar / biomass are unviable then a heat pump is ok, preferably with onsite electricity production from PV or similar.