Attic Heat Harvester
attic heat harvesting system, reducing heating cost


Supplemental home heating for the cost of running a light bulb

Optimising Controller Parameters

reduce heating costs - buy now Attic Heat Harvester Controllers have 11 user set parameters enabling you to customise the controller to your application and to achieve maximum system performance to reduce heating cost.

Parameter

a) minimum 'Attic - Room' temperature

b) maximum Room Temperature

c) maximum Attic temperature

d) Harvesting Fan air Flow rate

e) Harvesting Fan Power

f) Cooling Fan Power (option)

g) electricity cost per kWh

h) Metric or English units

i) Current Day and Time

j) Weekday Heat On Time

k) Weekend Heat On Time
Default Value

3C (5.4F)

23C (73.3F)

43C (110F)

1220 cmh (706cfm)

80watts

60watts

0.14 currency units

Metric

Mon:00:00

0:00

0:00

a) Minimum 'Attic - Room' temperature

This parameter determines when the attic heat harvester system fan turns on impacting heating system efficiency and the heat moved from the attic to your home. Increasing the setting increases heating system efficiency but reduces total heat transferred.

We suggest during periods of the year when maximum attic temperature exceeds room temperature by modest amounts set the parameter to a low value, e.g. 1.5 °C maximising heat transfer. When the difference is high set the parameter higher, e.g. 4 °C maximising heating system efficiency.

heating system efficiences graph
System Efficiency vs
Attic - Room Temperature Difference
Heat produced vs attic - room temp
Heat Produced and Efficiency vs
Attic - Room Temperature Difference

The first chart shows heating system efficiencies vs attic - room temperature difference. All conventional heating systems with the exception of systems that use heat pumps can achieve an efficiency of from 0.25 to 1. Heat pump base systems can achieve an efficiency of up to 3, the heat they use is free BUT they consume a lot of electrical energy to transfer the heat. The attic heat harvester system also uses free solar energy but uses very little electrical energy to transfer the heat.

The attic heat harvester efficiency is proportional to the attic - room temperature difference and to the air flow rate achieved. At a typical air flow rate of 1500cmh (880cfm)and an attic - room temperature difference of 0.5°C the attic heat harvester efficiency exceeds that of heat pump systems, at a temperature difference of 5°C the efficiency is 15 times more!

The second chart shows the impact of increasing the minimum attic - room temperature difference parameter which reduces the heat transferred but increases the system efficiency.

b) Maximum Room Temperature

In general setting maximum room temperature low reduces heating costs. With attic heat harvesting however when day time attic air temperatures are expected to be high and night time outdoor temperatures are expected to be low raising the maximum room temperature can reduce the need for expensive conventional heating systems at night reducing total heating costs. You can further reduce heating costs by watching your local weather forecast and setting the maximum room temperature parameter appropriately.

To reduce heating cost during periods of the year when you can use both attic heat harvesting and your conventional heating system this parameter should be set significantly higher than the conventional heating system thermostat to get as much cheap heat as possible. This is best achieved by reducing the conventional heating system thermostat setting.

Conventional heating systems use electricity in standby mode. We suggest turning off your conventional heating system during periods of the year when you only use attic heat harvesting, the electricity you save will exceed that used by the attic heat harvester so the heat harvested will be better than free!

c) Maximum Attic temperature

Hot attics increase home cooling costs. The controller can be ordered with an option to turn on an attic fan to exhaust hot attic air when attic temperature exceeds the maximum attic temperature reducing cooling costs, set this parameter to suit your home and local weather.

d) Harvesting Fan air Flow rate

System performance and performance calculations depend on achieved harvesting fan air flow rate which in turn depends on the harvesting fan used, the ability of the heated air to exit the heated area and move to other areas of your home, and on the air duct diameter, length and straightness.

The default air flow rate is set to suit the fan we supply and to an average flow rate achieved.

Anemometers are available to measure air flow rate achieved, the controller air flow rate parameter should be set to this value to provide accurate performance data.

e) Harvesting Fan Power

The electrical power consumed by the harvesting fan impacts heating system efficiency and cost. The fan we provide consumes 80 watts. If you use a different fan this parameter should be set to suit the fan to ensure accurate controller efficiency and cost data.

f) Cooling Fan Power

This parameter should be set to suit the cooling fan you use. If the parameter is incorrect the calculated cooling cost will be incorrect.

g) the electricity cost per kWh

The controller heating and cooling cost calculations use this parameter, it can be obtained from your electricity invoice.

h) System Unit selection, either Metric or English

Set units to suit your preference.

i) Current Day and Time

To increase heating system efficiency the controller has an integrated programmable timer synchronised to the frequency of your local electricity supply, and permits you to delay the daily heat harvesting start time. To use this feature the current time and at least the weekday or the weekend heating start time must be set.

j) Weekday Heat On Time

Set this time to delay the weekday heating start time, if the value is set to 00:00 heating start time will not be delayed.

k) Weekend Heat On Time

Set this time to delay the weekend (Saturday and Sunday) heating start time, if the value is set to 00:00 heating start time will not be delayed.