AOAC Sustainability Project.

Ground Source Heating

 

What is it?

Ground Source Heating utilises naturally occurring heat energy form the ground in order to provide building heating. This can be done via water source heat pumps using buried ground loops on bore holes where in winter temperature is significantly above that of the surface. The ground loops are a vessel through which a transference medium (water generally) is passed to absorb naturally occurring heat. That medium is then passed into a building to provide space heating and, in some cases, to pre-heat domestic hot water on fluoride cooling.

 

How?

There are 3 elements to a ground source pump:

 

The Ground Loop: A length of pipe buried in the ground either in a borehole or horizontal trench. The pipe is a closed circuit and filled with water and antifreeze which is pumped around the pipe absorbing heat from the ground. The ground loop can be vertical, horizontal, spiral or a coil.

A Heat Pump: This converts the energy gathered by the ground loop into useful energy. The pump has 3 main parts, an evaporator to absorb heat from the ground loop, a compressor to pressurise a gaseous refrigerant to the temperature needed for the heat distribution circuit and a condenser which give up heat to a hot water tank and feeds the distribution system.

Heat Distribution System: This consists of under floor heating or radiators for space heating and in some cases water storage for hot water supply.

 

Benefits

The system does not need and external fuel and is designed to heat an entire building.

Average CoP is around 3-4 making it an efficient way of heating a building.

 

Disadvantages

Ground hoops require large land area.

Costs typically 2-3 times more then conventional heating.

 

Savings

On average the saving is £400-£800 on your domestic heating bills and 2-8 tonnes of Co2 per year, dependant on the type of fuel being replaced.

 

 

 

Solar Water Heating

 

What is it?

Like PV systems Solar HWS’s utilise the natural energy stored in light but instead of using it to create electricity they use it to heat water.

His obviously decreases heating bills.

 

How?

For a Solar HWS all thats required is a hot water boiler system, solar water heating panels and connective piping between the two containing heat activated or thermostatic valves. The sun shines onto the panels (ideally aligned south facing at an angle of 20-500) through which water is being pumped, this heats the water. Once the water has reached approx. 800C thermostatic valves open and allow heated water to flow into the main boiler until the water temperature falls sufficiently and the valves close again.

Typical panel sizes for commercial properties are approx 2.4m x 1.2m. Power outputs for such a panel in peak output conditions i.e. midday summer sun with no clouds, is 1.6kW, equivalent to 500W/m2 with a maximum water temperature of 87C.

These types of systems are only intended as supplementary systems.

 

Benefits

Low purchase, implementation and maintenance costs mean payback periods can be as little as five years.

CO2 reductions of up to 350kg/year and huge PR benefits make these systems highly viable for commercial properties.

Very few moving parts so lifetimes are around 25 years.

Pre-packaged panels allow easy and cheap fitment.

 

 

Photovoltaic Solar Panels

 

What is it?

PV’s are devices that can be used to convert the naturally occurring energy in light into useful electricity output. The field of PV systems has tremendous potential due to the abundance of light that is currently only minimally utilised.

 

How?

PV Cells are made of special materials called semiconductors, such as silicon, which is currently most commonly used. When light strikes a cell it transfers energy to the semiconducting material. In turn this dislodges electrons allowing them to flow freely and form a current.

The cells will also contain one or more electric fields that act to force freed electrons to flow in a certain direction. By connecting metal contacts to either side of the cell this current can be extracted from the cell. Multiple cells are then connected together into arrays which are then contained in panels for fitment.

 

Benefits

PV systems do not produce any greenhouse gases and each kWp can save approx 455kg of CO2 emissions per year, adding up to about 11 tonnes over a systems lifetime.

 

Costs

For commercial applications these panels come in several main varieties:

 

PV Tiles: These look nearly identical to normal roofing tiles but are covered in a Photovoltaic layer. The advantage of this type of panel is that they can be blended into existing tiled roofs with minimal visual appearance. Typical costs are approx £920/m2 with peak power outputs of 92W/m2.

Roof Mounted PV Panels: These are large panels of solar cells that cen either be face mounted on a sloped roof or made to free-stand on a flat roof. Obviously these panels are much less visually attractive but have definitive power gains and cost decreases over the tiles. Typical peak power outputs are 130W/m2 with costs of £630/m2.