Solar Heat Harvesting

Supplementary home heating from a new inexpensive, simple and reliable Conservatory Heat Harvesting system (CHH) costs 10 to 50 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 Heat Harvesting CHH and AHH systems.

use free solar heat to reduce heating costs

Cornwall home with Conservatory Heat Harvester installed

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

Mullion outdoor and indoor temperatures

The chart shows conservatory and outdoor air 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 Attic Heat Harvester (AHH) System was retro-fitted to the ground floor conservatory to reduce heating costs, and increase home comfort levels.

At times of the year when Solar Heat Harvesting 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, consumes just 40 watts 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.

October 2017 Home Heating and the Mullion Conservatory Heat Harvester (CHH) system efficiencies are shown in the chart. The CHH system efficiency is proportional to the Conservatory – Home air Temperature Difference. Other heating system efficiencies are mostly independent of temperatures.

At an air temperature difference of just 1°C our Conservatory Heat Harvester system efficiency exceeds all others. In the system 2016 and 2017 performance charts below, the average air temperature difference was 9°C achieving an efficiency of 40.

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 Conservatory Heat Harvester systems 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 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 conservatory solar heated 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.