Solar Space Heating System

Increasing the Heating System Efficiency to Reduce Heating Cost

Attic Heat Harvester Controllers are used in Attic and Conservatory Solar Space Heating. The controller has 11 parameters, whose type is defined below, that users can set enabling you to customise the controller to:

1.  Suit your temperature and operation Time Wish Parameters (TWP)

2.  Produce Accurate system Performance calculation Parameters (AP)

3.  Be Compatible with the other components used in your application Parameters (CP)

4.  Change system Performance to maximize heat transferred or to maximize system efficiency Parameters (PP)

Parameter Default Value Parameter type
a) minimum 'Attic – Room' temperature3C (5.4F)PP
b) maximum Room Temperature23C (73.3F)TWP
c) maximum Attic temperature43C (110F)TWP
d) Harvesting Fan air Flow rate1220 cmh (706cfm)AP
e) Harvesting Fan Power80wattsAP
f) Cooling Fan Power (option)60wattsAP
g) Electricity cost per kWh0.14 currency unitsAP
h) Metric or English unitsMetricTWP
i) Current Day and TimeMon:00:00TWP
j) Weekday Heat On Time0:00TWP
k) Weekend Heat On Time0:00TWP

a) Minimum 'Attic – Room' temperature
This parameter determines when your Solar Space Heating System fan turns on impacting heating system efficiency and the heat moved from the attic/conservatory to your home.

The chart below may help you to understand the following 3 paragraphs.

Increasing the setting increases heating system efficiency. Reducing this value does the opposite but more solar heated air is transferred to your home. From 2015 the controller automatically increases the parameter value above the preset value and increases system efficiency during periods exceeding a few days when the maximum daily attic/conservatory temperatures are high increasing the system efficiency and reducing heating cost. The value is automatically decreased it to the user preset or the system default as the averaged temperatures decrease.

Solar Heat Harvesting Efficiency is proportional to the source-destination air temperature difference. To maximise the solar heat transferred we suggest during periods of the year when maximum attic temperature exceeds room temperature by modest amounts that you set the parameter to a low value, e.g. 1.5 °C, this will increase the amount of heat transferred reducing the operating hours of your conventional home heating system and reduce heating costs.

When the difference between the maximum attic temperature exceeds room temperature by large amounts set the parameter higher, e.g. 4 °C or greater, this will increase the heating Solar Heat Harvester system efficiency as shown in the following chart for Attic Heat Harvesting and Conservatory Heat Harvesting.

How Solar Heat Harvester Systems reduce Home Heating Costs
Attic Heat Harvester reduce heating costs

Attic Heat Harvester reduce heating costs

b) Maximum Room temperature
When the room temperature reaches or is above this pre-set value the Solar Harvesting system is turned off. If your central heating system is on and it's thermostat is set higher than the maximum room temperature set in the controller solar heat harvesting will not operate. To reduce heating costs ensure that the central heating thermostat is set to a lower temperature than the Attic Heat Harvester Controller Maximum Room Temperature parameter.

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/conservatory heat harvesting, the electricity saved will considerably exceed that used by the solar heat harvester and 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 Blower/Fan air flow rate
To get accurate Solar Space Heating performance figures from the controller the air flow rate parameter should be set to suit that achieved by the fan at the hot air outlet in your home, this is dependent on the fan used and on any back pressure experienced by the fan which will reduce the air flow. Anemometers are available which measure air flow.

In Attic Heat Harvesting Systems the hot air is fed via insulated ducting to a low room in the home. The air flow through ducting is impacted by the air duct diameter, length and straightness, each impact the back pressure. In homes that are relatively airtight it is vital that there is a return air path into the attic or the fan back pressure will be dramatically increased and the airflow greatly reduced.

The Conservatory Heat Harvesting fans we suggest have a quite accurately defined airflow provided the fan does not experience back pressure. If heat is being harvested from conservatories it is vital that there is a cool return air path into the conservatory or the airflow will be dramatically reduced.

e) Harvesting Blower/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 (Imperial)
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. Many different fans can be used, we can supply a number of these, this parameter should be set to suit the fan you are using.