The term biomass heating refers to the combustion of plant based organic materials for the purpose of heating a volume of air. Biomass fuels fall into two main categories:

• Woody resources from sustainable sources such as fast growing trees or subsiduary waste products such as sawdust or recycled untreated pallets.
• Non-woody resources such as animal waste and the secondary organic output of activities such as oil seed rape and sugar cane processing.

These fuels are repositories for solar energy – energy from the sun is captured via the process of photosynthesis and stored by the plant, then released by combustion.

The important point to note is that fossil fuels such as oil, coal and gas that have taken millions of years to form are excluded from the definition – a biomass fuel will be carbon neutral. The CO2 released when energy is generated from combustion of the biomass is balanced by the CO2 absorbed during the fuel’s production. In the case of fossil fuels, when burned they release carbon dioxide that was captured millions of years ago and as such only increase current total CO2 levels.

For space heating purposes, the biomass will be utilised either by the primary heating source in a room (for example, a wood burning stove) or the secondary heating source of the building (for example, a pellet fed boiler connected to the central heating and hot water systems).

Biomass systems are often bulky and so can require extensive storage space for both fuel and machinery. Unlike other sustainable heating solutions (such as heat pumps) the fuel will need to be sourced (often bought) and so fuel and transportation costs, as well the environmental impact of production and transportation will need to be taken into account.

With careful planning and appropriate sourcing of fuel, a biomass heating solution will have both environmental and economic advantages, providing a carbon neutral heating solution with lower running costs than traditional (gas, oil, coal) powered alternatives.

The younger sibling of the ground source heat pump (GSHP), the air source heat pump (ASHP) is an exciting development in heating technology. They operate on the same principles as the under-ground alternative, but draw thermal energy from the air rather than underground – air at ambient temperatures is passed over a finned heat exchanger and heat energy extracted into the evaporator of the heat pump. ASHP’s release up to four times more heat energy than they consume in powering their various components and so offer an energy efficient, sustainable heating solution. They are best coupled with well insulated, energy efficient buildings and under floor heating systems.

Currently (summer 2007), a 6kW ASHP costs around £3,500 with a larger 12kW pump weighing in at about £6,000. This excludes the cost of the distribution system such as an under floor heating installation.

As air is the medium from which thermal energy is extracted, the installation of an ASHP is relatively straightforward – there is no need to dig extensive trenches or drill the borehole necessary for a GSHP. The pump is sited at a suitable distance from building and connected via pipe work buried in trenches. ASHP’s are designed to operate with minimal noise pollution.

The basis of heat pump technology is something that we are all familiar with as it is the same as that used in refrigerators or air conditioning units. The core function of these units is to take heat from the ground and transfer it to a building for the purpose of heating water. This heated water is commonly used for space heating but can additionally be used as the basis for all hot water provision in the building given an additional boost from a complementary boiler system.

Heat pumps consume energy in the form of the electricity used to power the pump; this is a relatively efficient use of energy producing between two and four units of heat for each unit of electricity consumed. The system is at it most efficient when used to run an underfloor heating system.

Heat is gathered from a ground loop; this is constructed from lengths of pipe in a closed loop and filled with a blend of water and antifreeze. This liquid is pumped through the pipework loop and absorbs heat from the surrounding ground. The ground loop is either buried in trenches to the depth of around a meter or sunk into a borehole. The borehole option requires less ground area, but is more expensive to excavate and install than a trench.

The pumped liquid bears its absorbed heat to the heat pump where the evaporator takes the heat from the liquid and the compressor circulates the gaseous refrigerant and compresses it to the desired temperature. The condenser then transfers the heat to a hot water tank from which the heat distribution system is fed. In turn, the heat distribution system heats space through under-floor piping or wall mounted radiators.

At the time of writing; from a cost perspective this method of heating is cheaper than all options except mains gas. The high cost of electricity from solar photovoltaic (PV) cells means that supplying the electricy needs of the system from that source is not currently cost effective and off-peak electricity provisioning should be considered.

For the coldest times of the year it is appropriate to consider an additional secondary source of heating such as a multi-fuel or wood burner that should be fuelled from sustainable sources.

A heating system based around this technology is a cornerstone of a healthy house design, providing a lower air temperature, surface heating, healthy heating solution.

From the Romans to present day, underfloor heating has been a good idea. Underfloor heating provides gently radiating heat from the whole of the floor surface. This radiant heat is similar to the heat from the sun, heating the occupants of the room directly rather than the air around them (must admit I’ve never fully followed that, but that’s what I’m told!). As such the whole of the room is heated and the hot / cool spots and convection air currents caused by traditional radiators avoided. Thus dust movement is reduced and humidity levels in the air maintained – the moted health benefits for underfloor heating lie in these attributes.

Is it green? Underfloor heating has a couple of green credentials:

• It requires a lower water temperature (and therefore consumes less energy) than traditional radiators.
• Heat wastage is minimised as the air is not dried-out or circulated unnecessarily.

The underfloor heating pipes can be set into the screed of a structural floor slab or laid on-top of the floor slab in a layer beneath the floor covering. Maintenance of the pipe work is minimal once installed and should last as long as the floor it is set into.

Running costs are attractive at up to 25% less than a traditional radiator based system running off the same heat source. Additionally, installation costs are comparable.

Many heat sources can be used in conjunction with underfloor heating. Perhaps the current system of choice is a ground source heat pump … of which more coming soon …

Through recent technological innovations it is now possible to insulate buildings to such an extent that no heating system is required to maintain comfortable temperatures.

There are varying categories of super insulated buildings.

Zero Heat Building
This category of building, through insulation and draft proofing, requires no additional heat source, except for in extreme conditions. The heat provided by the occupants’ bodies, household appliances, the sun and artificial lighting is sufficient for ordinary requirements.

To achieve this typically insulation of 500mm of cellulose fibre will be required in the roof, 300mm of expanded polystyrene in the floor, 250mm of filled wall cavity and triple glazed windows and doors will be necessary.

Zero CO2 Building
A zero heat building when supplied with electricity and any additional heating from renewable sources becomes a zero CO2 building. It must produce zero net emissions of carbon-dioxide over its lifetime.

The Autonomous Building
Take a zero CO2 building; remove it from mains services (gas, water, electricity and sewage) provide it with electricity generation, sewage processing and water collection solutions (all of which are renewable, sustainable and ecologically sound) and you have an autonomous building.