Solar Home Space Heating systems use a Fan/Blower to efficiently transfer free solar heated hot air from hot to colder areas of your home. Annual system running costs to supply a significant part of your home heating typically range from £1 to £10.
Once you have decided to install a Solar Space Heating system there are a number of things to decide, one is what fan to use.
We have tested many different fans to determine those most suitable, our suggestions are based on five criteria:
a) The airflow the fan generates – this requirement is mostly dependant on the size of your home, attic and conservatory.
b) How each fan performs when it experiences back pressure which reduces the fan airflow achieved. Maximum back pressure for each of the fans we suggest is included in the SHH Suggested fan tables referred to below. In conservatory heat harvesting applications, provided that the airflow is not impeded on it's route through your home, nor by small diameter main or return air holes, back pressures are low. However in Attic heat harvester applications where a relatively straight and smooth air route cannot be achieved, or where long or small diameter ducts are used the fan can experience considerable back pressure.
c) The fans efficiency calculated as cmh/w - (cubic metres/hr/watt), the air flow produced per watt of electricity used, this will directly impact your annual system running costs, the higher the efficiency the lower the running cost.
d) How quiet an operating fan is, this can be important for conservatory heat harvesting systems. In Attic heat harvesting systems noise in the home made by the attic fan is usually greatly reduced due to its remoteness and to attic floor insulation.
e) How much power the fan uses.
Ordered Fan performance comparison tables for a range of suggested fans for low and medium back pressure applications are included in this website. The ordered tables are: a) Airflow, b) Back Pressure,, c) Fan Efficiency, d) Noise Levels, and e) Fan Power.
We suggest that in Attic Heat Harvester applications for homes with large attics you use a 450mm fan fitted to a funnel that reduces the duct diameter to suit a 350mm (14inch) or 301mm (12inch) diameter air valve and insulated duct. In the Balerno Solar Space Heating application a 305mm air valve and insulated duct was used.
a) The size of your home
The fan size that best suits your home generally depends on the size / volume of your home, and attic or conservatory. Most of the fans we recommend can be connected to operate at one of two speeds, at the slower speeds the airflow is lower but the airflow per watt, which impacts the system efficiency, is higher.
For large homes with large attics we generally recommend a fan which consumes 90 watts that is fitted with a funnel. In a single floor home this can achieve an air flow of 3500cmh, in 2 and 3 floor homes the air flow is reduced due to the longer duct lengths to typically 2500 or 2000cmh respectively.
For medium sized homes and medium to large conservatories we suggest either a 200 or 230mm diameter fan with maximum rated airflows 750 or 970cmh respectively.
For small homes/conservatories we suggest one of two 200mm diameter fans that, with air flow holes of at least the fan diameter, that can be connected to run at one of two speeds, and generate an air flow of from 310 to 750cmh when no back pressure is experienced. Fan power consumption ranges from 3.4 to 28 watts.
b) Back pressure experienced by the fan
The effectiveness and annual saving you win from your solar heating system will, in part, depend on how much back pressure the hot air flow experiences on its journey through your home, or to the outside world if the air can easily escape.
In attic heat harvesting applications backpressure depends on the size of the air duct, how long it is, how straight it is, and how continuous it is.
In the Attic Solar Space Heating system at the Balerno, Edinburgh installation a 450mm diameter fan was used together with a funnel that reduced the air flow diameter from 450mm to 305mm to suit a 305mm inner diameter insulated duct that went through 2 floors to the kitchen and living room below.
Sometimes it is not possible to eliminate most of the back pressure, fans are available that can cope with medium backpressure.
In conservatory solar space heating applications generally fan backpressure can be avoided by making the air holes at least as large as the fan diameter, and by ensuring that the heated air can easily flow through your home and back to the conservatory. Sometimes gravity air valves will be need to be fitted in the homes internal walls.
c) Fan operating noise level
In some applications low fan noise is important, the fan noise level, where available, for all fans we recommend are included in the fan comparison table referred to previously.
d) The fans Efficiency
Fan efficiency can be expressed as airflow/watt, this impacts the annual running cost of your solar space heating system, the greater the efficiency the less the cost.
e) The fans Power consumption
The lower back pressure fans can be connected to operate at either a low speed to consume less power, or high speed when greater power is consumed. Ordered fan power consumption table.
We have also produced a specifications table for recommended fans that can operate in medium backpressure applications.