Energy is life. The quality of life is directly related to the easy availability of energy.
We will no doubt one day find ways of providing energy freely to all, without disturbing the health of the natural enviroment, but until then we must minimise the impact buildings have, with designs that reduce day to day and embodied energy consumption, as far as possible.
Renewable technology notes
Biomass Boilers burn wood pellets, chips, or logs ,to power boilers heating water in the hot water cylinder, which may be connected to a central heating or hot water system. A log burner may be fitted with a back boiler to provide water heating.
Carbon emissions are much lower than emissions from fossil fuels, especially when the fuel is sourced locally.
Solar Photovoltaic Panels generate carbon free electricity from daylight, even low winter light. A 4kw array in the UK on a south facing roof will on average generate 3400 kwh of energy per year. A 24 sq. metre area of roof is required to accommodate 16 to 18, 250 watt, PV panels.
Site generated electricity can be used to power lighting, heating, household appliances and immersion heaters and can be stored in battery packs.
Battery storage enables unused electricity generated during the day, which would otherwise be exported to the national grid, to be stored in a battery, usually on a garage wall, for use in the evenings when the house is fully occupied and energy demand is high.
Solar Thermal Panels collect carbon free energy from direct sunlight, or cloud diffused sunlight, to heat the hot water cylinder. A south facing array of 6 sq. metres would provide 60% of hot water requirements per year for an average 3-bedroom home in the UK.
Solar Thermal Stores are large, highly insulated hot water cylinders that store domestic hot water efficiently for long periods of time. They deliver mains pressure hot water to kitchens and bathrooms and low pressure hot water to radiators or underfloor heating circuits. They can be interconnected with Solar Thermal Panels, Solar PV Panels and Heat Pumps, as well as conventional boilers, log burners with back boilers, Aga boilers, or electric immersion heaters and are designed to manage a number of heat inputs and outputs to suit any preferred application.
Air Source Heat Pumps convert heat from a low temperature source to a higher temperature. They are designed to deliver either domestic hot water (air to water systems), or space heating (air to air systems).
Ground Source Heat Pumps use underground pipe work as a low temperature heat source and therefore require sufficient land or garden to accommodate the installation.
Heat Pumps are an energy efficient and environmentally friendly way of producing energy for the home. They have much lower carbon emissions than conventional gas or oil fired boilers and are very low maintenance.
Domestic Hot Water is one of the largest consumers of energy in UK homes (20% to 25%), but is an area of design where renewable energy technology offers huge potential for reducing household bills.
A well-designed supply delivers continuous mains pressure water to hot taps at 50 °C to 55 °C and at 40 °C to radiators and towel warmers. Hot water should be stored at or above 60 °C to prevent legionella bacteria build up.
If a suitable south facing roof is available, a design that integrates Solar Thermal Panels with Solar PV Panels, connected to a Solar Thermal Store, is one of the most energy efficient ways of heating water. Water in the Thermal Store is heated by a combination of Solar Thermal Panels during sunny, or cloud diffused sunny periods and an immersion heater powered by Solar PV Panels during daylights hours and by battery stored electricity, in the evenings and can benefit from economy 7, low cost electricity at night, if necessary, ensuring plenty of hot water first thing in the morning.
Heating super insulated homes, requires very little energy. A surprising amount of heat gain is produced internally by people living in the house, cooking activities, domestic appliances and passive solar gain.
Optimum internal temperatures of 20 °C in living areas and 18 °C in bedrooms can easily be achieved with one or two warm water radiators, or by electric radiators and night storage heaters, or by warming air in the ventilation supply ducts.
Well-designed systems allow temperatures in each room to be adjusted, or turned off. In warm water systems temperatures can be adjusted from a centrally located control unit wired to communicate with individual radiators.
A classic way of heating homes designed to Passive House Criteria (PHPP), is to warm the air in the supply duct of the ventilation system with a low voltage electric element, or with a warm water wrap. Whole house heating in this way, which heats the whole house rather than individual rooms, is energy efficient and low cost and is the preferred heating method for houses designed to PHPP thermal calculation criteria.
Ventilation is essential to our sense of comfort and wellbeing in highly insulated homes. MVHR systems (Mechanical Ventilation with Heat Recovery), are an excellent way of delivering the correct quantity of air to each room, with healthy levels of relative humidity (40% to 60%) and C0₂ concentration (350 to 1000 ppm). Continuous air changes remove pollution, dust and odours from the air and prevent mould growth or condensation build up on internal surfaces. Fresh, filtered pre-warmed air is pushed around the home by small 20 watt motors, costing around £80 a year to run.
A heat exchanger recovers 95% of wasted heat from moisture laden stale air extracted from kitchens and bathrooms and uses it to pre-warm fresh air in the supply duct, transferring the heat without mixing the air.
It is important that MVHR systems are designed and installed by specialists. They require once yearly maintenance checks and twice yearly filter change.
Cooling is essential in super-insulated homes, when on hot summer days opening windows and doors is insufficient to bring internal temperatures down to comfort levels.
For homes with MVHR ventilation, a cooling unit can be fitted to the heat exchanger to reverse its function and deliver cool fresh air throughout the house instead of warm air.
Similarly, where homes are heated with Heat Pumps, reversing their function will deliver cooling instead of heating.
It is important that cooling units offer easy control to enable them to be switched on during daytime periods and off in the evenings.
Passive House Design is an energy standard where the anticipated energy performance of a home can be predicted through the use of PHPP energy modelling software. It is favoured by home owners who prefer to see the energy performance of a design demonstrated by calculation, based on floor and wall surface areas, construction details, local climate data, air leakage test results and commissioning records.
Domestic Renewable Heat Incentive (RHI) is a government financial incentive to promote the use of renewable heat to reduce UK carbon emissions and meet its renewable energy targets.
Four technology types are eligible for the scheme:
- Biomass boilers and stoves.
- Air source heat pumps.
- Ground source heat pumps.
- Solar thermal panels.
Feed-in Tariffs (FIT’s) is a government scheme to encourage uptake of small scale renewable electricity generation and is eligible for tariff payments for each KWh of electricity generated which may be used to power home electrical appliances, making a saving on home electricity bills, as well as reducing the carbon footprint of the property.