Solar Heat Harvesting

Heating System Efficiency has a huge impact on heating costs and on the planet, the greater the efficiency the less the cost.

This webpage shows UK 2017 heating efficiencies and details of a new available extremely efficient Solar Heat Harvester system that achieves a home heating efficiency 10 to 50 times higher than all the others.

The following table was derived from SEDBUK 2017 data. SEDBUK stands for 'Seasonal Efficiency of Domestic Boilers in the UK', it is an energy efficiency rating scheme which was developed by boiler manufacturers and the UK government to enable a fairer comparison of the energy efficiency of boilers.

Home Heating System TypeSystem Efficiency Figure
Natural gas condensing boiler 0.9
Natural gas non condensing boiler0.7
Fuel oil condensing boiler0.85
Fuel oil non condensing boiler0.7
Electrical Heating1
Air source heat pump 2.75
Ground source heat pump3.5

The charts below show the efficiencies of some of the heating system types tabled above, together with the efficiencies of Attic Heat Harvesting (AHH) and Conservatory Heat Harvesting (CHH), our Solar Heat Harvesting systems.

The energy efficiency of the heating systems in the table are fixed i.e. they are not dependent on air temperatures. In contrast the efficiencies of Solar Heat Harvester systems are directly proportional to the hot – cold air temperature difference, and to the rate of airflow achieved. The impact of both temperature difference and air flow rate are shown in the charts below.

The huge advantage of Solar Heat Harvesting Systems is that very high heating efficiencies can be achieved at very low cost. Even at an air temperature difference of just 1°C the efficiencies of both Attic (at airflow rates above 800cmh) and Conservatory Heat Harvester systems exceed that of the other heating systems. At an air temperature difference of 5°C the energy efficiency is five times greater.

Data for Solar Heat Harvesting Systems in the charts was derived from a thermodynamics equation shown below.

Typical annual air temperatures differences achieved by our Solar Heat Harvesting systems range from 5 to 10°C and efficiencies achieved range from 20 to 50.

AHH heating system efficiency

Conservatory heat harvester system efficiency

Heat in Hot Air

The heat, P, energy transferred by our Solar Heat Harvester Systems is based on the following thermodynamics equation for forced air heating systems:-

P = q * ρ * c * Δ T / 3600

Where in S.I. units:
P - power [kW]
q - flow rate [m³/h]
ρ - density of fluid [kg/m³]
c - specific heat of fluid[kJ/kgK]
Δ T - temperature difference[K]

‘ρ’ the density of dry air at STP and 'c' the specific heat of air at constant pressure are constants that can be included in the constant K which for SI Units is 0.000362 and Imperial Units is 0.00341

In S.I. units ∴ P [kW] = (0.000362 * volume of air moved in m³/h * Temp difference in °C

In 'Imperial' Units P [kW] = 0.000341 * volume of air in ft³/min * Temp difference in °F

The Home Heating System Efficiency is given by:

Efficiency = Heat created at the required destination (P) * the running time / the energy used to create it

The home heating system efficiency is inversely proportional to the energy used to create the heat.

Our Attic Heat Harvester systems use an efficient fan that consumes 80 watts, the flow rate achieved is very dependent on the system ducting length and straightness. The flow rate achieved at the Balerno installation, where the air path was long, tortuous and restricting was 1000cmf, the fan is capable of achieving a flow rate without restrictions of 3500cmf.

Our Conservatory Heat Harvester Systems use either a quiet running brushless DC driven fan that provides an air flow of 500cmf and consumes 40 watts at maximum speed, or a quiet running brushless DC driven fan that provides an air flow of 1000cmf and consumes 99 watts at maximum speed.