Solar Space Heating System

Secondary home heating from a new inexpensive, simple and reliable Conservatory Solar Space Heating system (CSSH) costs 10 to 100 times less per kilo Watt Hour (kWh) than from conventional home heating. The heat is free, the cost to transfer it very small, by using a Conservatory Heat Harvester you can reduce heating cost.

This chart shows the 2017 cost per kWh, a standard unit of heat, for a range of common Home Heating systems and the cost from Solar Space Heating CSSH and ASSH systems.

use free solar heat to reduce heating costs


You can reduce heating costs by using a system that has a low cost per kWh.

Cornwall home with Conservatory Heat Harvester installed

Mullion outdoor and indoor temperatures

The chart shows conservatory and outdoor temperatures at a Mullion, Cornwall 1992 built home, for 9 days in April. The maximum conservatory air temperature exceeded 20°C, a comfortable home temperature, by from 5°C to 25°C for more than 8 hours every day showing that much free solar heat is available.

In late 2015 a modified secondary home heating system that replaces the expensive costly heat from the current oil fired central heating system was retro-fitted to the ground floor conservatory to reduce heating costs, and to reduce high conservatory temperatures making it far more comfortable.

At times of the year when Solar Space Heating cannot be used e.g. winter months, the home's normal heating system is used.

The system custom Attic Heat Harvester Controller continually monitors the temperatures high in the conservatory and in the home. When the home temperature is below a user pre-set maximum, and the conservatory air temperature is sufficiently high, the controller turns on a quiet efficient brushless motor driven fan that, at maximum speed, initially consumed 40 but now consumes 7 watts (a new recently developed extremely efficient fan was fitted in 2018) and has an airflow rate of 500 cmh.

Mullion Conservatory Heat Harvesting system diagram

The air circulates through the home and returns to the conservatory at a low level. Gravity closed air vents prohibit air movement between the conservatory and the home when the fan is not operating.

The controller calculates and records system performance parameters, which can be viewed on its integrated display. Parameters saved include: current transferred heat and efficiency, total transferred heat and efficiency, total annual operating cost, blower hours, average temperature difference, and the maximum and minimum conservatory temperature. The controller has a number of user settable parameters enabling system performance to be adjusted.

The two charts below show Conservatory Solar Space Heating efficiency and airflow rates for four different recently available energy efficient fans, operated at both low (LS) and high speeds (HS), together with the efficiency of common home heating systems. The fan fitted in 2018 to the Mullion home is a W1G200-EC87-25 which is connected to operate at low speed. The Conservatory Solar Space Heating system efficiency is proportional to: a) the airflow rate the fan achieves b) the fan power consumption and c) the conservatory – home temperature difference as shown in the charts below.

At an air temperature difference of just 0.5°C our Solar Space Heating system that uses hot conservatory air efficiency exceeds all others. In the system 2016 and 2017 performance charts below which used a far less energy efficient fan, the average air temperature difference was 9°c achieving an efficiency of 40.

solar heat harvesting system efficiency comparison

solar heat harvesting system efficiency comparison

The following charts show Mullion Conservatory Heat Harvesting System 2016 and 2017 annual performance and 2017 monthly performance.

Conservatory Heat Harvester annual cost and heat produced

Solar Heat Harvesting annual heat, fan hours and efficiency to reduce heating cost

In 2016 the system provided 661kWh of heat at a total cost of £2.54. In 2017 the system provided 801kWh of heat to the home at a total cost of £2.89.

The system efficiency during the two years was 39 and 41, this means that the system is:

    more than 40 times as efficient and less expensive than electric heating
    more than 14 times more efficient and less expensive than an air source heat pump
    more than 11 times as efficient and less expensive than a ground source heat pump

Both annual and monthly performance are weather dependant. At Mullion, generally most heat is transferred in the spring and autumn, and in June, July and August little heat is required as shown in the following charts.

Conservatory Heat Harvester heat and cost per month


CHH monthly operating hours and efficiency expoiting free solar heat

The Mullion weather in 2017 was somewhat unusual, the spring weather was good, but autumn weather was unusually cool, however the automatic Conservatory Heat Harvesting system makes the most of any weather only transferring hot conservatory air when it is both required and available.

The surprising high efficiency of Solar Space Heating systems that use hot conservatory air results from the thermodynamics equation for Heat in Hot Air and to the very low energy required to transfer the air due to the high efficiency of the brushless DC electric fan motor used. The system efficiency for 2018 when the new fan was used will be some 7 times higher and the operating costs 7 times less!

The Mullion Home comfort levels early and late in the year were increased because hot conservatory temperatures were decreased in early spring and late autumn when the solar heated air was being transferred by the solar heat harvesting system to warm the home. During the months when the oil fired central heating was turned off home temperatures were increased to the maximum value preset by the user in the controller during cooler weather spells.

Fossil fuels in our world are being depleted at a very alarming and unsustainable rate. By using Solar Home Space heating using hot conservatory air in your home you can reduce your fossil fuel use and your current home heating system use and the associated costs by £10's to £100's of pounds every year.