Radiator cover

Hi,
all the DIY progs. are hot for radiator covers - not a naked radiator in sight.
However it has always seemed to me that enclosing a radiator must reduce the heat output, even where most of the heat is from convection not radiation.
So I was pondering over installing a silent fan in a radiator cover, to encourage the flow of air and thus redistribution of heat.
The first obvious solution is one or more 'silent' PC fans as they are compact, come in a housing with screw holes, and are designed to run for long periods/continuously. I suspect you could even link them to a heat sensor so they only ran when the radiator was hot. However this would also require a PC power unit to reduce the voltage, which increases the cost and the footprint of the unit.
Any suggestions as to suitable 240V solutions? Bathroom fans are too big and noisy.
TIA Dave R
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"David W.E. Roberts" wrote on 17/12/2003 :-

What a good idea....
I don't think the normal PC fans will have adequate capacity to move the quantity of air needed, however....
The big main frame computers and often control panels use a 240v AC fan of much larger diameter. 6" seems to be a common size. They are very well made, designed to last in continuous use for lots of years and can be picked up from scrap merchants for just a few pence.
Add a mains voltage thermostat and you have a much better means of controlling local room temperature than those temperature controllers fitted in place of the valve.
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Harry (M1BYT)...
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when
which
That depends on how many you use!

I think you will find these big fans way too noisy! The best way I can see, would to be to have a few of the PC 80mm case fans (maybe 4 or 5) Sick a resistor in so they are not going full chat (To reduce the noise) (A variable resistor may be nice, so you can adjust the speed of them) You can also add a thermistor, somehow glued to the rad with some kind of heat transfer glue (If there is such a thing) You would also need a small plugtop transformer and a nearby socket (Unless you felt like buying an alarm PSU, and running wires to all the rads you want to mod!) (connect the PSU to the boiler wiring, and the fans will only run when the CH is on, removing the need for the thermistors!)
Sparks...
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On 17/12/2003 "Sparks" opined:-

Having made use of both the high quality mains units and the small 12v ones, I can assure you that the mains ones are much quieter. The slower the airflow through the fan the quieter they are, assuming there is no mechanical noise from the bearings. Mains powered computer grade cooling fans are extremely quiet.
I accept your point that there would no good reason to run the fan, unless the radiator was hot. I would therefore suggest wiring two thermostats in series with the fan(s). One which closes when the radiator is hot and a second one which closes as the room cools, controlling room temperature.
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when
which
Unfortunately 6" diameter is likely to be far too large. I was thinking of a maximum footprint of about 3" including housing to allow it to be mounted in the horizontal plane underneath the radiator to blow upwards. This would also conceal the fan(s). I was also not thinking of using a room thermostat because that involves wiring external to the radiator cover. I was intending to rely on the TRV and just activate the fan(s) when the radiator itself was hot (i.e. the TRV said the room temperature was too low. I was assuming a sensor which was designed for cooling PCs or PC chips could fall within the required temperature range.
Sounds like a fun project (despite my total lack of electronics expertise).
Will price up probable bits, including PSU vs transformer plug, to see how ridiculously expensive it might be.
I assume that a couple of fans might make enough difference, as two PCs seem to keep our small home office warm - radiator very rarely comes on. I only need to compenste for the loss of efficiency caused by the cover, so a relatively gentle flow of air should do.
Cheers
Dave R
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"David W.E. Roberts" wrote on 17/12/2003 :-

You could perhaps incline a 6" fan so as to fit it in, or use a 240v tangental fan, similar to those used in fan heaters.

You could simply mount the room thermostat on the cover. It would be a shame to go to this much trouble, yet not make it able to provide some worthwhile room temperature control.

You can buy a simple mechanical fixed temperature thermal switch for around a pound each. Maplins and Farnell sell them in a range of temperatures, able to switch mains voltages.

A replacement PC power supply tends to be more expensive than buying a complete new PC case including PSU.
Certainly doing the job with low voltage would be a safer option, but I think you will require many more of the small 12v fans than you assume.
A little like loud speakers, fans work best via a baffle. If there is an easy route from the input to the output, then that will be the route that the air flow will take. So you should be looking at either providing forced air flow or a convected air flow, but not both.
Had you a little more electronics experience, then I would suggest that the fan speeds be variable, based upon the difference between desired and actual room temperature.
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Harry (M1BYT)...
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Yes, it would then be called a fan convector. A real fan convector is more expensive than a radiator, but much smaller for the same output. Unfortunately, many look a bit 1970s, but I can live with that for my conservatory.
Christian.
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On Wed, 17 Dec 2003 10:31:13 -0000, "David W.E. Roberts"

The normal derating factor suggested by the HVCA is 30%

You could use a small wall wart and drop the voltage to under-run them. Then they will be quieter as well.
Even with this cost, they will be less than a fan convector. I believe that Myson makes a bare bones one of these for building into your own woodwork.
For any of these solutions, don't forget that the TRV needs to be located outside the box, or one with a remote sensor used.
Then a pipe thermostat to turn on the fans?
Getting expensive, isn't it......

.andy
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Good idea. I have been looking at fan assisted radiators for our local church. Quite expensive! However, their feature is that they blow the air out at ground level ( below 4" ). This causes a strange air flow effect that makes the hot air hug the ground for 15 to 20 feet. The idea is that you heat the air around the people rather than the ceiling.
May be worth experimenting/googling to see if there is any science about this...
Colin
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On 17/12/2003 "Colin" opined:-

That is the reason why those fancy ceiling fans are used in winter. Warm air rises to the ceiling, ceiling fans draw the warm air down towards the room occupants.
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Harry (M1BYT)...
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We've got regular ones in our church and they have worked pretty well. A useful tip for you is to arrange the wiring so that the heaters come on one by one on their individual low limit stats rather than having a master thermostat switch them all on and off - when the sudden noise/quiet is likely to be unacceptable.
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Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
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