Radiator Fans rather than upgraded Radiators with ASHP

michaels

SO we all know that with more efficient low flow temps for an ASHP it is likely that rads may be undersized.  The correct option is of course to fit larger rads but I was wondering if Radiator Fans could be used instead as a short term solution?

With rads it is easy to find the heat output at different flow rate but I can't find out any info on how much adding fans might increase output.

ecoCalm Radiator Fan Booster 2.0 for Home, Smart Radiator Ventilator with Thermostat Controller, Suitable for Radiators Such as TYP21, TYP22, TYP32 (Duo Set) : Amazon.co.uk: DIY & Tools

Reed_Richards

Powered radiator fans certainly increase the heat output of a radiator.  I suspect that the amount of increase depends on how well the fans are positioned, as well as fan speed.

matelodave

Probably a good idea to include the cost of peak rate leccy whilst they are running 

However, depending on your level of intellectual curiosity you could have a shufti at this - https://www.engineersedge.com/heat_transfer/convective_heat_transfer_coefficients__13378.htm which suggest that the velocity of the moving air also has a part to play in calculating the heat gain.

Lots of other info on t'interweb if you want to get into the weeds

michaels

Reed_Richards said:

Powered radiator fans certainly increase the heat output of a radiator.  I suspect that the amount of increase depends on how well the fans are positioned, as well as fan speed.

All true of course, but what matters is if they add 5% or 50% for which there is no info online that I can find.

born_again

Reed_Richards said:

Powered radiator fans certainly increase the heat output of a radiator.  I suspect that the amount of increase depends on how well the fans are positioned, as well as fan speed.

While the above is true, they also cool the radiator down faster, meaning heating will be kicking in to heat it back up.
Seem to remember a similar long running thread on this subject before.

Ouch £99 that is a expensive set of fans.

matelodave

Grind your way through this - https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html however the cheap and easy way to see it it works is to get a couple of computer fans off Amazon or E-bay to increase the airflow over the radiator and do some measuring.

You could measure the flow temps of the rad (in and out) using a differential thermometer to find the DeltaT across the rad either without the fan and then with the fan to see by how much the Dt changes.

This should indicate the effectiveness of the fans. by increasing the Dt as more heat should be extracted from the rad with the fans running. You could then play about with fan speeds and number of fans to see what happens.

Although its probably the wrong time of the year to do that but it would give you a project for next autumn 

stripling

michaels said:

SO we all know that with more efficient low flow temps for an ASHP it is likely that rads may be undersized.  The correct option is of course to fit larger rads but I was wondering if Radiator Fans could be used instead as a short term solution?

With rads it is easy to find the heat output at different flow rate but I can't find out any info on how much adding fans might increase output.

ecoCalm Radiator Fan Booster 2.0 for Home, Smart Radiator Ventilator with Thermostat Controller, Suitable for Radiators Such as TYP21, TYP22, TYP32 (Duo Set) : Amazon.co.uk: DIY & Tools

How can a fan 'increase' output? All it is doing is redistributing (around the room) what is already there. Larger radiators not only increase heat from the heat pump they also increase efficiency by increasing the volume of water circulating.  

michaels

stripling said:

michaels said:

SO we all know that with more efficient low flow temps for an ASHP it is likely that rads may be undersized.  The correct option is of course to fit larger rads but I was wondering if Radiator Fans could be used instead as a short term solution?

With rads it is easy to find the heat output at different flow rate but I can't find out any info on how much adding fans might increase output.

ecoCalm Radiator Fan Booster 2.0 for Home, Smart Radiator Ventilator with Thermostat Controller, Suitable for Radiators Such as TYP21, TYP22, TYP32 (Duo Set) : Amazon.co.uk: DIY & Tools

How can a fan 'increase' output? All it is doing is redistributing (around the room) what is already there. Larger radiators not only increase heat from the heat pump they also increase efficiency by increasing the volume of water circulating.  

The rate of transfer of heat from the rad to the air will depend on the delta t between the air touching the rad and the rad. Circulate the air past the rad quicker than natural convection and the air touching the rad will be colder on average hence increasing the rate of heat transfer.

Think about how it feels colder when the wind is blowing because you lose heat quicker.

shinytop

michaels said:

stripling said:

michaels said:

SO we all know that with more efficient low flow temps for an ASHP it is likely that rads may be undersized.  The correct option is of course to fit larger rads but I was wondering if Radiator Fans could be used instead as a short term solution?

With rads it is easy to find the heat output at different flow rate but I can't find out any info on how much adding fans might increase output.

ecoCalm Radiator Fan Booster 2.0 for Home, Smart Radiator Ventilator with Thermostat Controller, Suitable for Radiators Such as TYP21, TYP22, TYP32 (Duo Set) : Amazon.co.uk: DIY & Tools

How can a fan 'increase' output? All it is doing is redistributing (around the room) what is already there. Larger radiators not only increase heat from the heat pump they also increase efficiency by increasing the volume of water circulating.  

The rate of transfer of heat from the rad to the air will depend on the delta t between the air touching the rad and the rad. Circulate the air past the rad quicker than natural convection and the air touching the rad will be colder on average hence increasing the rate of heat transfer.

Think about how it feels colder when the wind is blowing because you lose heat quicker.

I can confirm this is true; we have a fancoil radiator in the kitchen (think car radiator with a fancy cover) that gives off next no heat unless the fan is switched on, when it emits a nice stream of warm air that warms the kitchen.  And of course a car radiator has a fan for the same reason, to increase the amount of heat dissipated for the same water flow. 

FreeBear

matelodave said: You could measure the flow temps of the rad (in and out) using a differential thermometer to find the DeltaT across the rad either without the fan and then with the fan to see by how much the Dt changes.

Throw in a flow sensor (on the return side is usually best), and coupled with an Arduino or ESP, you could calculate how much energy is being dissipated.

shinytop said:I can confirm this is true; we have a fancoil radiator in the kitchen (think car radiator with a fancy cover) that gives off next no heat unless the fan is switched on, when it emits a nice stream of warm air that warms the kitchen.  And of course a car radiator has a fan for the same reason, to increase the amount of heat dissipated for the same water flow. 

Got a plinth heater in my kitchen. Depending on water temperature, it will kick out 2kW at low speed, and 2.4kW at high(flow temp of 75°C). But as my flow temperatures are between 40°C and 60°C, actual output is more like 1-1.5kW..

stripling

@michaels
The rate of transfer of heat from the rad to the air will depend on the delta t between the air touching the rad and the rad. Circulate the air past the rad quicker than natural convection and the air touching the rad will be colder on average hence increasing the rate of heat transfer.
Think about how it feels colder when the wind is blowing because you lose heat quicker.

That's such a nice, clear, succinct explanation. Thank you. 😁