Attic Heat Harvester
1 floor attic heat harvesting system


Heat your home for the cost of running a light bulb

Differential Temperature Controller

attic heat harvester, differential temperature controller The versatile Differential Temperature Controller is based on a powerful micro-controller. The system functionality is defined by a program that is pre-programmed into the device by the manufacturer. Attic Heat Harvester Ltd can modify the system functionality by developing different programs to meet the requirements of innumerable other applications.

When operating as a control system for an attic heat harvesting application the core function of the Differential Temperature Controller is to compare two temperatures. If temperature 1 exceeds temperature 2 by a user preset amount a relay is closed, supplying ac power to a fan.

Many other functions are also integrated into the controller, these include: air valve control; calculation and display of system performance data, user ability to pre-set a number of system parameters to precisely suit the application, and system test features.

In the attic heat harvester guise the Differential Temperature Controller has a 2 line x 8 digit 'back lit' LCD display, 3 key buttons, 2 temperature sensor inputs, and 2 or 3 relay outputs. One relay supplies ac power to a fan, a second is used to open and close the air valve, and the third optional relay is used to supply ac power to an optional attic cooling fan.

AHHS differential temperature controller


The Attic heat harvester display has a number of display modes that:

a)  Display system status and firmware version during the power up sequence - this information should be provided should you need to contact the manufacturer with a controller related query.

b)  Display attic and room temperature - the 'normal' display mode

c)  Display attic heat harvester performance data

d) Display the user pre-settable system parameters which can be changed by using the + and - keys

e)  Display the results of system tests

f)  Enables attic heat harvester performance data to be reset, i.e. cleared

g)  Enables the fan and air valves to be manually operated

Attic Heat Harvester Performance Monitoring

Attic heat harvester performance data display mode is selected by pressing and holding the 'MODE' for 1 second then releasing it.

The Differential Temperature Controller displays attic heat harvester performance data in the following sequence:

a)  The current power being generated in kWs, and the current system efficiency, e.g. 1.2 = 120%, and 34 = 3,400%

b)  The total power in kWh and the total system efficiency for the system since it was last reset

c)  The fan operating hours and the average attic - room temperature since the system was last reset

d)  The total number of hours that the fan has been off when the attic temperature exceeded the room temperature, and the average temperature difference during this time - this gives the user some idea of the unused solar heat available

e)  The maximum and minimum attic temperatures

f)  If the attic cooling option is purchased when the system was ordered, the number of hours that the fan has run in attic cooling mode

The attic heat harvester performance data display sequence can be terminated by the 'MODE' key.

Differential Temperature Controller Pre-settable Parameters

System Parameters configure the controller to meet your applications needs, these can be displayed and edited as required by pressing and holding the MODE key at least 2 seconds then releasing it, then by using the + and - keys as needed.

The Differential Temperature Controller configurable parameters are:

a)  Attic - Room temperature. This enables the user to set how much higher than the room temperature the attic temperature has to be before the fan is turned on. This parameter impacts a) the system efficiency, - increasing the difference increases the system efficiency (and vice versa), and b) the power transferred - increasing the difference can decrease the power transferred as the fan runs for less time.

b)  Maximum Room Temperature. This enables the user to preset the room temperature at which the fan switches off preventing further heating.

c)  Fan Flow - this parameter defines the air flow rate for your system. It is used to perform system power and efficiency calculations and if incorrect calculation accuracy is impaired. If Attic Heat Harvester Ltd supply the system components and they are installed as suggested this parameter will have been correctly set.

d)  Fan Power - this parameter defines how much power the fan consumes. The parameter is used to perform system efficiency calculations and if incorrect calculation accuracy is impaired. If Attic Heat Harvester Ltd supply the system components and they are installed as suggested this parameter will have been correctly set.

e)  Metric or English units - this parameter defines whether the display is to operate in °C and cubic meters per hour cmh, or °F and cubic ft per minute cfm.

A more complete description of the DTC keypad and LCD Operation is here and the information on the differential temperature controller technical specification is here.