Heating control problem

[Tricky Dicky]

The bungalow we moved into at the end of Summer has a gas fired CH system w ith a Worcester 27i combi-boiler. To control the system we have a Horstmann Centaurstat 7 programmable thermostat in the lounge and with the exception of the lounge and bathroom all other radiators have TRVs. The system works OK in the main except for one of the bedrooms which has had a window remov ed and a conservatory added, this is fully double glazed including the roof .

However, this conservatory room is used as a second reception room and we a re finding it loses heat much quicker than for instance the lounge. It does heat up fairly rapidly once heat gets to the radiators but because the lou nge retains its heat better the system does not fire enough to maintain tem perature in the conservatory room. To overcome this I find I have to boost the temperature on the thermostat but then the lounge becomes too hot the rest of the house is OK as the TRVs prevent overheating.

When we first moved in the thermostat was in a hallway and situated above a radiator. The hallway like the lounge retains heat well this combination c aused us to swap the thermostat to the lounge and swap the TRVs in the loun ge with normal valves and put the TRVs on the hallway radiator. This improv ed operation in the rest of the house except the conservatory room.

I want to find a way to boost the heat in the conservatory room when needed but keep it at bedroom temperatures at other times. I am considering repla cing the valves with TRVs in the lounge a bypass would still be available t hrough the bathroom radiator. I know that a room controlled by a room stat should not have TRVs but the way I see it is that by doing that I can boost the temp as required in the conservatory room and rely on the TRVs to prev ent other rooms getting to hot. I know one alternative is to place the ther mostat in the conservatory room but feel it might prove problematic when we want to keep it at bedroom temperature whilst wanting to maintain a higher temp. in the lounge.

Am I on the right lines or are there any other suggestions?

Richard

[Biggles]

Use 2 thermostats - existing one in lounge and new one in conservatory, wired in parallel?

Biggles

[Tricky Dicky]

That would not stop the lounge overheating it would just nullify the lounge stat and pump heat through the standard radiator valves on the lounge radiator.

Richard

[Colin Stamp]

It sounds like the rads in the lounge are too big. Size is a bit critical for the rads in the room with the room stat since they define how much heat the rest of the house gets access to. Really, the room with the room stat needs to be the one that needs the highest boiler duty cycle, then the TRVs in the other rooms can all do their job. Since it sounds like there's more than one rad in the lounge, have you tried turning one off?

Once you've got the boiler running enough to heat the conservatory, you will be able to control the temperature in there using the TRVs. You could even add programmable heads to them if you want.

I wouldn't put TRVs in the lounge because the system will become very twitchy when you start turning them down to try to achieve what you want. You're likely to end up with the room stat never being satisfied and calling for heat 100% of the time.

Cheers,

Colin.

[dennis]

Do the job properly and zone it. TRV systems are just a tiny step better than the old systems they used to install with just a boiler stat.

[Tricky Dicky]

Colin

I have only one rad in the lounge and although sizeable so is the room and although I have not done the calculations I would say it is appropriate. It looks very much like it may mean re-siting the stat in the bedroom/conserv atory putting TRVs on the lounge rad and trying to control the heat as you suggested.

Richard

[Tricky Dicky]

Dennis

That thought had passed through my mind but it would cause considerable dis ruption to re-plumb the conservatory/bedroom as a separate zone at the mome nt and although it is still on the cards when we eventually re-do the bathr oom where the zone valve would need to be placed since the boiler is sited in what was formally the airing cupboard where a HW cylinder was housed.

Thanks Richad

[Roger Mills]

The only solution which will actually work is to create a separate zone for the conservatory with its own programmable stat. That way, it becomes independent of the rest of the house, and you can heat it when you need to without affecting anything else.

Re-plumbing may be a bit inconvenient, but there's no reason why you can't use Hep2O - or equivalent - which makes it relatively easy to install continuous pipes all the way from boiler to conservatory without needing any joins or bends. Depending on the size of radiator needed, you may get away with 10mm pipe - making it even easier.

[Dave Liquorice]

The OP says the system works well apart from the room that has been modified by having a gert big heat sink attached to it, aka the conservatory.

So either that additional heat loss needs to be stopped, fit door, folding paneling or WHY between room and conservatory or increase the heat into that room/conservatory, fit rad in conservatory, higher output rad in room.

[Colin Stamp]

I probably should have added "relative to the ones in the bedroom/conservatory combo". It was there in my mind...

He also says that the system is able to adequately heat the modified room whilst the room stat in the lounge is demanding loads of heat, so whilst there is no-doubt a big imbalance, it's not an uncorrectable one. Hence my comment about needing to have the room stat in the room which needs the highest duty cycle. A quick, dirty fix is to reduce the heat input to the lounge so that it matches the modified room in terms of heat input/loss. Reading between the lines, the lounge isn't short of heat at the moment.

By all means try to even out the imbalance between the heat input/loss ratios but, unless you go silly, that modified room is still likely end-up having the worst ratio, so it should really be the one with the room stat and no TRVs. Then the system should work as well as a TRV system can (which is actually pretty well, IME.)

Cheers,

Colin.

[Colin Stamp]

Sounds like a good plan. IME a decent TRV setup is the next best thing to having a zone in every room, but only if the room stat is in the room that needs the most boiler time.

Cheers,

Colin.

[Tricky Dicky]

Dave

You are right about the conservatory being a heat sink. The previous owners who added the conservatory slightly reduced the original bedroom, there is quite a large radiator in the conservatory part and a smaller one in what is left of the original bedroom. These radiators provide adequate heat for the whole area and from cold the room heats up quite comfortably in about h alf an hour. The problem only manifests itself once the lounge heats up bec ause in there the heat loss is far less so once the system goes into temper ature maintenance mode the radiators in the conservatory/bedroom just do no t get enough heat into them to counter the heat loss. To counter this I hav e to bump up the temperature setting on the stat this does not affect the r adiators in the rest of the house because the TRVs keep the the rooms at th eir set temperatures. The lounge though with no TRV (because of the room st at) starts to get warmer than needed. When we use the room with the conserv atory as a bedroom, when my grandson comes for his weekly overnight stay, w e have a sofa bed that he uses. Due to the reduced room size when extended this sofa bed extends into the original window opening which is the only fe asible separation point where a door could be placed thus preventing that a s a solution. We do have a curtain with a thermal lining across it even tha t hangs slightly askew to get around the foot of the bed, as a bedroom this arrangement leaves the bedroom relatively comfortable. It's when we use th e whole room as a second reception room and try to maintain a temperature s imilar to the lounge that we have the problem. As I said as long as heat ge ts to the two radiators they do an adequate job of heating the place up it' s the dual use of the room that's causing the problem. As a bedroom we are OK with the cooler temperature and this is why I am hesitating to do the si mple thing of moving the stat into the room as it will possibly prevent oth er parts of the house reaching adequate temperatures when set on a cooler s etting. This is why my original proposal of re-equipping the lounge radiato r with a TRV despite having a room stat seemed the answer. The thinking beh ind it was if the stat and TVR were set to the same temperature between the m they would maintain the lounge at the desired level. However, if more hea t was required in the conservatory/bedroom the stat could be turned up, the TVR on the lounge radiator would prevent that room getting any warmer just like the other TVRs in the other rooms already do. As the boiler fired up to attain the new set temperature the only radiators getting additional hea t would be the conservatory/bedroom and as these radiators already have TRV s the temperature would not exceed the maximum required. As the bathroom ra diator does not have a TRV it would provide an effective by pass should all TRV equipped radiators close their valves.

Richard

[harryagain]

However, this conservatory room is used as a second reception room and we are finding it loses heat much quicker than for instance the lounge. It does heat up fairly rapidly once heat gets to the radiators but because the lounge retains its heat better the system does not fire enough to maintain temperature in the conservatory room. To overcome this I find I have to boost the temperature on the thermostat but then the lounge becomes too hot the rest of the house is OK as the TRVs prevent overheating.

When we first moved in the thermostat was in a hallway and situated above a radiator. The hallway like the lounge retains heat well this combination caused us to swap the thermostat to the lounge and swap the TRVs in the lounge with normal valves and put the TRVs on the hallway radiator. This improved operation in the rest of the house except the conservatory room.

I want to find a way to boost the heat in the conservatory room when needed but keep it at bedroom temperatures at other times. I am considering replacing the valves with TRVs in the lounge a bypass would still be available through the bathroom radiator. I know that a room controlled by a room stat should not have TRVs but the way I see it is that by doing that I can boost the temp as required in the conservatory room and rely on the TRVs to prevent other rooms getting to hot. I know one alternative is to place the thermostat in the conservatory room but feel it might prove problematic when we want to keep it at bedroom temperature whilst wanting to maintain a higher temp. in the lounge.

Am I on the right lines or are there any other suggestions?

Richard

The nub of the problem is that the heat source in the conservatory is too small. There is a huge heat loss from any conservatory and the heating system is usually sized on the assumption that the conservatory will not be used in very cold weather. Usually there is a door between the conservatory and the rest of the house. If you are not prepared to increase the size of the heat source/radiator etc, you would probably be best to have a portable heat source for the conservatory for occasional use in cold weather. Any buggering about with heating sensors/thermostats is not likely to succeed.

Often conservatorys have a separate heating "zone" from the rest of the building, this is always the best way.

Attempts to heat any conservatory will be very expensive in heating costs.

[Jeremy Nicoll - news posts]

A wireless stat that you can keep in the lounge if you're not using the conservatory, but move to the conservatory when you are using that, plus a TRV in the lounge (to limit heating there when you're trying to heat the conservatory) might help.

[Tricky Dicky]

What are the advantages/disadvantages of scrapping the room stat and going fully TRV on all radiators except the bathroom, which will provide the bypass, and having a programmable timer?

Any suggestions for a programmable timer, with it being a combi boiler it only needs to control the CH. As a backup there is a connection to have a remote frost stat connected to the boiler which I think I will take advantage of.

Richard

[Colin Stamp]

I think that would be a pretty inefficient way of running the boiler. Also, the bathroom will get a lot more heat than it needs.

It sounds like putting a TRV in the lounge and moving the room stat to the conservatory room will do what you want. As Jeremy says, a wireless room stat would be more flexible still. Just remember to turn the TRVs right up in whichever room you put it.

Cheers,

Colin.

[Scion]

Tricky Dicky put finger to keyboard:

If your need to heat the conservatory to higher than bedroom temperature is only occasional then I'd suggest an oil filled radiator with inbuilt thermostat. These are available with selectable on/off time controls if required.