Boosting central heating output in one room?

[ericmark]

I have rooms set so living room cool at night and mothers down stairs bedroom cool in the day, (upstairs bedrooms radiators rarely come on anyway) however every so often something happens and we want to heat a room which was cool. Mother going to bed in day for example.

I can quickly change the setting on the radiator, and the radiator does get hot, but it takes ages to get heat from radiator into the room, I am considering a fan aimed at the radiator, I know you can get fan assisted radiators, so what about a fan aimed at standard radiator?

But how big? a normal room fan as used in summer, or a small fan USB powered, the radiator is under the window, and furthest from boiler, wondered if anyone has tried it? Also considering control, thought maybe my beer brewing thermostatic control, at least as a test, has anyone already done it, no point reinventing the wheel?

So any one tried it, and if so how did it go.

 

[Mottie]

My mum has a remote wireless thermostat. Sometimes she’s in the lounge, sometimes she’s in the bedroom reading or watching telly. Probably inefficient but she takes the thermostat with her when she changes rooms so that whichever room she’s in is the same temperature as whatever the thermostat is in. Both rads in those rooms don’t have TRV’s.

 

[ban-all-sheds]

How often does the need for this arise?

I know that electric heating is expensive, but if the need is infrequent, and when it does arise it is short term until the CH is doing its thing, why not just get a fan heater and avoid faffing about trying to fan the radiator?

 

[ericmark]

I tried the Horstmann HRFS1 programmable wireless thermostat

this also could be carried room to room for a time it worked, but it gradually lost it's range and would fail to switch off, the room would get like a sauna, seems it has no fail safe, if anything blocks the signal only way to get it to work is for it to be manually set hotter or colder than setting then brought back to setting. Once bitten twice shy so decided not to get a second one.

The electronic TRV heads with wifi have two way coms, and to date have worked well, and given time the room will go to exactly the temperature set, that is not a problem any more, the problem is speed of change. Set to 18°C because day time and room not used that is what temperature the room goes to, however if my mother decides she wants to go into the bedroom, turn the heating to 20°C and radiator gets hot, however it takes a long time for that heat to get into the room.

Can't blame the control, the radiator is hot, but it can take 3 hours to warm the room, so once I can get home to pick up the controller I was considering a fan aimed at the radiator to remove the heat from the radiator and transfer it into the room, if I put the sensor on the return pipe then once whole radiator is hot the fan will start, once room is warm enough the TRV will close the return pipe will cool and the fan will stop.

In essence a copy of how a Myson radiator works, theory is good, but wondered if anyone has already tried doing it. If so how well did it work, at the moment can't get home to pick up bits required due to snow, is it worth it.

 

[WhydidIstart]

Hi, I've used a fan aimed at a radiator to help warm a room quickly before. I found a large room fan set on low works best. It creates the best flow of air across the whole rad and is nice and quiet. Small usb style fans seemed to be noisier and only created a small amount of airflow local to only part of the rad.

As a more permanent fix I found fitting a larger rad plus the reflective foil behind it made a big difference to how fast the room heats up.

You could also make sure your boiler is heating the rads nice and hot, i.e. 75C or higher, as long as that doesn't purse a danger to anyone in the house.

 

[JohnD]

I fitted longer radiators, or swapped singles for doubles, so the rooms would heat up faster after a week away. A long radiator also heats the room more evenly than a short but tall one. As TRVs are fitted, the large radiator does not overheat the room.

Modern boilers are very unlikely to be underpowered, unless you have a really large house

If you can do basic plumbing, it is not a difficult job.

I've noticed that housebuilders often fit very meagre radiators, presumably to pare costs to the bone.

 

[John D v2.0]

Agreed with the above suggestions, we have an old fan from a redundant cooker hood, attached to a plug and set to the slowest speed. It works extremely quickly with oversized radiators to warm the room, and it's also excellent for drying washing in a flash.
Not completely health and safety compliant, but it works well.

 

[ericmark]

I think as soon as I can collect the thermostat I will set up a test, I don't really want the fan running with a cold radiator so will collect thermostat first, I would hope to find the fan only runs when the temperature setting for room has changed, and when room is being just held at a temperature the fan will turn off as the TRV works reducing the temperature of radiator and so the temperature of return water.

If it works then the question is do I build a unit using a STC-1000? or just use an Inkbird 308? £10 v £25 and with £10 still need to buy box cable and sockets. Or once I have worked out temperature can I used a fixed temperature device.

I have tried to set the room thermostat and programmer to go off just before the temperature rise then on again on temperature rise, however the slow speed of rise means the room thermostat in hall is some times satisfied before the electronic heads on the TRV have got rooms to target temperature, the hope is if I can speed up the change in room temperature it will complete before hall thermostat starts to cycle (it has built in anti hysteresis software) I think the best cure would be to hard wire some thermostats, however that is a lot of work.

 

[ericmark]

Today bedroom down stairs cold, 2°C outside about 2 inches of snow, the baby alarm in bedroom shows 19°C as did the TRV until I plugged in the fan, it dropped to 17°C and has now gone to 18°C target is 20°C oh just rechecked now 19°C I have lifted target to 22°C under normal conditions without fan looking at 3 hours to get that. Used a tower fan blowing between the fins from the TRV end so the TVR is getting the cold air.

At the moment no thermostat, just on 120 minute timer, the radiator has cooled right down, so it clearly does need a thermostat to stop fan once radiator is cold. In the half hour I have been writing this, the room gained 2°C which is amazing it would normally take two hours,

The fan is too big, it does the job well being tall and blowing down end of radiator, but just shifts too much air, however shows the idea works.

 

[SimonH2]

You could also make sure your boiler is heating the rads nice and hot, i.e. 75C or higher, as long as that doesn't purse a danger to anyone in the house.

Bear in mind that such a temperature will almost certainly stop a boiler condensing and significantly reduce it's efficiency. To keep condensing, the return (including bypass flow) needs to stay below about 54˚C

I fitted longer radiators, or swapped singles for doubles ...

I started doing that at the last house - working room by room as I was "doing them up". I'm going to have to do something more drastic (and less aesthetic) in the short term here as only one room has an adequate radiator - so they all need upgrading but I can't get under the floors (laminate which can't really be lifted without making a mess of it) to properly alter the plumbing.

Modern boilers are very unlikely to be underpowered, unless you have a really large house

Indeed, especially if you have a Combi as that forces them to be grossly overpowered unless you have such a huge house that a combi would be unlikely to be suitable anyway.

I've noticed that housebuilders often fit very meagre radiators, presumably to pare costs to the bone.

Yes, cutting costs to the bone, together with architects that believe "what the computer says" about the required heat input - yeah, it'll heat the room, but barely manage to get it up to temp in the first place.

 

[ban-all-sheds]

Indeed, especially if you have a Combi as that forces them to be grossly overpowered unless you have such a huge house that a combi would be unlikely to be suitable anyway.

Or have a house which is not well insulated by current new-build standards. Some boilers have a 10:1 modulation ratio, so it ought to be possible to have a combi which is not grossly overpowered.

 

[ericmark]

Experiment in mothers house, after the radiator cooled found both supply and return pipes cold which should not have happened, swapped batteries in the eTRV and it now seems to work OK, the eTRV should flash the red LED to warn of flat battery this did not happen, and it was reporting around 2.86 volt not sure if battery was over discharged or if fitting new batteries re-calibrated the valve? But room seems to be heating quicker now without the fan.

My own house the problem is items in front of the radiator, the Myson which by design is fan assisted got around that problem, it is very quick to heat the room, but with old non modulating boiler also quick to cool once boiler has turned off. Noise is not noticed during the day, but at night when watching TV with volume low so not to annoy neighbours, when the fan kicks in you do notice it. Mine simply switches on/off, but the more modern type has variable fan speeds which auto select to maintain the temperature. The Myson does not alter water flow when the fan kicks in, so does not need a by-pass valve to allow water to return when valves have closed, with all Myson this is not a problem, it will control the modern boiler with the return water temperature well, but not sure what would happen with a mixture of Myson fan assisted and standard radiators?

My Myson pre-dates the TRV and that was one of the reasons for fitting it, independent thermostatic control to the room thermostat, it is over 25 years old and still going strong. Only maintenance is a drop of oil on the sintered bronze bushes.

With a modern modulating boiler they should work well, allowing a very fast warm up, and since the boiler modulates it would not switch off, it would just auto reduce fan speed, however EvoHome and the like would not work, the building management systems for the Myson fan assisted make EvoHome seem rather a cheap option.

So there seems to be a place for a hybrid, a radiator which will heat most of the time without fan assistance, but when changing temperatures will energise a fan for fast warm up. My thoughts were if a thermostat was connected to return, when running normal the TRV will have reduced water flow so return is only warm, so fan would not be triggered, but when there was a high demand for heat, then the TRV would be fully open and the return from radiator would get warmer so could trigger the fan, should the fan over cool the radiator it would be switched off again.

Since it will cost me nothing to test, I already have a suitable thermostat normally used to brew beer with, still on the cards to set up a test. However I think with a eTRV it may fail because of the built in anti-hysteresis which reduces the speed at which the valve opens, it opens a small amount at a time to stop over shoot, so may not open radiator enough to keep the fan running. Once the snow has melted and I can get home, I will pick up a thermostatic controlled socket used to brew and give it a go.

 

[SimonH2]

So there seems to be a place for a hybrid, a radiator which will heat most of the time without fan assistance, but when changing temperatures will energise a fan for fast warm up. My thoughts were if a thermostat was connected to return, when running normal the TRV will have reduced water flow so return is only warm, so fan would not be triggered, but when there was a high demand for heat, then the TRV would be fully open and the return from radiator would get warmer so could trigger the fan, should the fan over cool the radiator it would be switched off again.

A couple of jobs ago I was involved in the office heating and cooling. We put electric head* valves on the Mysons connected to the same controller that controlled the cold water flow through the coolers. It would probably have been better to have had twin-coil fan coil units - but the Mysons were already in place.
So the Mysons were preset with thermostat on full and the cover screwed down to stop fiddling. When heating was required, the AC controller would open the valve, and the Myson fan would turn on using it's internal pipe stat. When room warm, the valve would be shut, and when the fan had cooled the internal pies it would then turn off.

* A lot like a TRV head, but with an electric heater element to warm up the wax capsule to operate it - apply power and it opens, remove power and it closes, with considerable lags. There are also motor driven ones (more expensive) and ones with a 0-10V control input (even more expensive).

Anyway, I think your idea has merit. If you have a large fan coil so it can also convect without the fan running, a logical control process could be to run the fan in variable speed mode to control the return water temperature. Under light demand, convection will be sufficient; as demand increases, return water temp will increase, and so the fan can start to be used.
A quick thought suggests the control algorithm needs care. If the fan responds too quickly you could have instability: TRV opens, return temperature goes up, fan starts up and runs too quickly, return water temp drops due to extra heat extracted, fan runs down, return water warms up, fan runs up, ...
Since you probably don't want the complication of setting up a PID controller, just severely limiting the rate of change of fan speed and running it in proportional mode only would probably deal with that. Eg, you set the system up so that fan stats with the return water at 30˚ and gets to full speed when it's got to 40˚ - but restrict the system so that the fan takes a minute or two to get from stopped to full speed (and vice-versa).

 

[ban-all-sheds]

Honestly, Eric - I can't help thinking that this has become, for you, more an exercise in playing with control systems than one of implementing a simple way to heat the room quicker on occasions.

 

[ericmark]

Honestly, Eric - I can't help thinking that this has become, for you, more an exercise in playing with control systems than one of implementing a simple way to heat the room quicker on occasions.

Probably correct, OK started genuine enough when battery went discharged and the system had a hiccup, but now just want to see if it works.

As to "SimonH2" the two controllers I have are the MH1210A and the STC-1000 in both cases I can set the difference set value STC-100 0.3ºC~10.0ºC and MH1210A 0.1ºC~30.0ºC also can set a delay start. Keeping what you have said in mind, I will use the MH1210A controller.

Interested with the electric head valves, I suspect those used for underfloor heating would work well. Unlike the standard radiator valves they are on/off.

I as you might have worked out from Ban's comments tried to do mothers house on the cheap, and even when I did spend, I did not spend enough, or too much depends on what you see as ideal. My house was so simple, I did not see a problem, my house is open plan, and the Myson circulates air and a single central thermostat controls whole house with TRV's fitted in bedrooms only to stop over heating if doors left open, it just works and has done for years. It took a long time to work out problem with mothers house, and when I did realised it was the bay windows acting as a sun trap. This means in her house the two main rooms need individual control, which TRV's give.

However that leaves how to control the boiler, I use two thermostats in parallel one in hall where there is also a TRV and one in kitchen not ideal place stuck on the side of the oven. However between them it works, in main kitchen one controls overnight and hall one during the day, not ideal but it works.

So when mums bedroom went cold I went into panic mode, what has gone wrong now was my thought. As said it was the batteries in the eTRV but did not work that out to start with.