Central heating Q

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Hi peeps,
The thermostat that controls our central heating boiler is in the, fairly small, hallway. Is this the best place for it?
If our living room and kitchen doors are closed and someone opens the front door won't the stat think the house is freezing and fire up the heating? If the stat's trying to get the hallway up to, say, 28 degrees, wouldn't the rads in other parts of the house be getting hotter than they needed to?
Our last house had the stat in the living room, which sounds a much better idea to me - if the main room is warm then the rest of the house is too, surely?
Also, I'm thinking of putting TRVs on all the rads so that the bedroom rads can be turned down in the daytime. I'm guessing that they can just be swapped with the existing valves (after draining down of course)?
If I did this would it mean that I could leave the stat where it was? It'd be a right pig to move and I'd rather not!
Any problems with this, or advice?
Ta,
Si
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If
rads
If the thermostat is in the living room and you have a gas fire- even for 'looks' - then the living room can be as warm as toast and the rest of the house freezing.
In the hall, with a properly balanced system, you should be able to get a acceptable temperature in the other rooms. If you them turn on the gas fire in the living room (for that warm look or a roll in front of the fire with the Mrs) you don't confuse the system.
Opening the front door etc will cause a 'burst' of the heating but that inrush of could air will need warming or it can give cold draughts in the other rooms.
On balance, I favour the thermostat in the hall.
Also, do a good job of draught excluding- that does wonders for the warm 'feel' of the house.
Regards
Brian
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Brian
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The thinking was along those lines actually!
We didn't want the rest of the house "freezing", as such, but bits of it could do with being a lot cooler than they are, the way things work at the moment - the bedrooms and kitchen get too hot so we were thinking of ways to a) lower the temps in those rooms which are not used a lot in the daytime and b) lower the running costs a bit.
I assume TRVs would help? Are they as easy to fit as they look?

That's a good point.

We've recently had double-glazing fitted, that should help a lot.
Thanks for the reply,
Si
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On Tue, 29 Jul 2003 20:04:58 +0100, "Mungo \"two sheds\" Toadfoot"

Yes they are. It used to be that you had to be sure to fit them so that the flow went in a specific direction. Nowadays most are reversible.
Otherwise, it's a fairly straightforward replacement exercise. One of the biggest pains tends to be removing the olive from the existing fitting to be able to put on the new nut and olive. From experience, I do think it's worth buying decent TRVs like Drayton, Invensys, Honeywell etc. A few pounds more but they do tend to last more than proportionately longer IME. Generally the expanding capsule in the head fails after a typical life of 7-10 years. You can buy spare heads and change them if the body is still sound.
Another option if the plumbing is appropriate could be to fit a zone valve with a timer/thermostat for the areas not wanted during the day. You could then use a setback thermostat to just drop the temperature a little.
I mentioned electronic thermostats in my other post. Another feature of these is setback where you can drop the temperature at certain times rather than off completely. Once adjusted suitably, you will get greater comfort. Also it can be less expensive to run if you just drop the temperature by 6 degrees or so overnight rather than completely off. The reason is that you then don't need the massive surge of heat in the morning to bring the building up to temperature and the overshoot and waste that that can bring. You do need to play around a little to set these effectively.

Yes it should, but you don't need to completely hermetically seal the place or you will get other problems.

.andy
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I wanted to do this and asked Honeywell for advice, as I have a Honeywell CM67 ChronoTherm (fancy thermostat). A very nice man at Honeywell sent me a wiring diagram for three zones and hot water, I actually wanted 4 zones and no HW control but it is easy to see how it is all wired up.
Cheers Jonathan
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Do have any figures to prove this? Unless it is sluggish UFH, setting the temp back does not result in greater economy. In the 1960s the electricity boards had a slogan "Lag It And Leave It", saying lag a cylinder and leave the immersion heater on 24/7. Under tests this was slagged as highly uneconomical. Switching the immersion on when needed or on a clock was proven to be far more economical.
In commercial buildings a low temp limit of 10C is maintained as under this temp the fabric of the building and its furnishings may be effected. A good optimum start stat as the Honeywell CM76 is the best way. It works out the right time to start the system to reach the target start temp.
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Actually yes, but first let me make the point that I did say *can* be less expensive, not *would* be. It would depend on the circumstances I am sure.
Remember that I said that I can gather all of the boiler data to a log on a PC. This includes fan speed (which relates to power level and gas usage), pump speed, flow and return temperatures and inside and outside temperatures, as well as whether the boiler is driving CH or DHW..
Last winter I did experiments over a few week-long periods with a 5 degree setback from 21 to 16 degrees and without setback at all. I took out the DHW use and looked at the CH only and matched 24 hour periods when the outside temperature pattern was similar.
There was, on average, a 3-5% lower use of gas when setback was used.

It isn't, but UFH is towards the extreme end of the scale in terms of thermal inertia. A house with conventional system and masonry walls still has a thermal inertia, albeit not as great.

At that point it probably did. WIth today's insulation, and I have a 100mm layer around my cylinder, the heat loss is negligible - a few watts. I therefore leave the hot water on 24*7 because it makes no sense to turn it off. It is very rare that the boiler does a hot water cycle between 2300 and 0700 unless hot water is drawn. Before you ask the question, yes I have data for that as well.
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What about comparison to optimised start and stop?

leave
The point is that the older cylinders can be equated to heating systems. Not so much today.
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That was with optimised start and stop. The controller does that anyway when ramping between two temperatures whether it has been completely off or just at a lower set point.

Probably. Really with decent insulation on the cylinder, whether the timer would allow the water to be heated 24*7 or just 16*7 becomes largely irrelevant.
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On Tue, 29 Jul 2003 19:00:47 +0100, "Mungo \"two sheds\" Toadfoot"

Yes.
Yes and no. There are two main components to heat loss - the first being what is lost through the surfaces (walls, floor, ceiling, etc.) and the second is heating the air. When you calculate heat losses for radiator sizing (or use a program to do it), the surface losses are accounted for by area, temperature difference and U value. The heat required to warm the air is calculated on the basis that you are heating the volume of air of the space at a certain number of air changes per hour (generally 1-2 depending on the room, more for kitchens and bathrooms.) Once the fabric of the building is warm, the heat loss through the surfaces varies with the temperature difference. If the building were completely cold and you turn on the heating, you would also be putting heat into the thermal mass of the building (mainly the bricks). However, once the fabric is warm, opening the door for a short time is only going to mean that the air needs to be reheated which does not require as long a run as the initial start from totally cold. This would mean that the radiators in the other rooms will run for longer than needed and the rooms will overheat if you just have standard valves.

Again yes and no. Provided that you have no extra heat in there such as a fire, you would get a reasonable result. Once you add heat from another source, the effect will be to cause the room to be warm enough and the CH only adding part of the heat. Its thermostat will be satisfied earlier and the rest of the house will be cooler than you may want. You can even get this effect if you have a smallish but well insulated room and you get a number of visitors. Each will add about 100W so 500W, which could be 25% of the heat requirement would be enough to throw the system off.
I don't think that there is a perfect place. Kitchens and bathrooms are out, so apart from hallways and stairs there isn't a huge choice.
Currently I have mine on an upstairs landing which is quite effective, but I do also have an outside temperature sensor and I can program the relative impact of one sensor vs. the other.

Yes they can. Remember not to put one where the thermostat is going to go or you will have two control systems fighting each other and the system will likely run quite cold.

You could do. One solution you might like to consider is to use an RF thermostat. The receiver can either go where the existing thermostat is, or close to the wiring centre or boiler (i.e. where you can tap into the wiring. With this arrangement you can take the thermostat where you like and control that. In this case, having a TRV on every radiator is more appropriate and then you simply turn the one in the room where the thermostat is to fully open.
In any case, it is worth fitting a decent electronic type thermostat because they operate more accurately and without the overshoot of the bimetallic strip type. That would also have the effect of reducing overheating in the rest of the house if the thermostat suddenly gets a cool blast of air.

.andy
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No, I didn't, but there is so I won't fit a TRV to it - thanks.

be
it -

stats
different
temperatures
I fancy that too. Sounds a bit 'spensive though :O)
Si
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On Wed, 30 Jul 2003 08:44:05 +0100, "Jonathan@Home"

My boiler (MAN Micromat) has its own control system and sensors.
The boiler itself modulates the burner via use of the fan speed and will give an output from 4kW up to full power. THe pump is internal and it modulates that as well, linearly. There are sensors for the flow and return water temperatures and it will run quite well just using those if you have a system with TRVs. As they adjust, it will vary heat output accordingly.
The manufacturer supplies an outside temperature sensor with the boiler which can be used to provide feedforward control. Since a house as a fairly substantial thermal time constant, sensing a change in outside temperature (especially if there is a relatively sudden one) allows the boiler to begin to adjust for it rather than waiting for the disturbance to show up in the house. This results in better temperature control and economy than can be achieved with an inside sensor alone.
One can also add an internal controller that is specific to the boiler, (but made by Siemens (Landis & Gyr) ). This hooks into the boiler and allows it to measure the actual room temperature. A conventional on/off thermostat or a proportional control type work by turning the heat demand on and off, albeit to good effect with a proportional type if adjusted correctly.
On this controller, it's possible to do all of the normal setback adjustments, and the boiler microprocessor begins to learn the heating behaviour of the house. You can also adjust the relative sensitivity and effect of the inside control and the outside control if you want to optimise further. One effect, for example is that sometimes the boiler will fire up at very low output just after sunset and the radiators will become tepid - about 40 degrees - increasing if need be. The boiler will also accept a conventional or proportional controller, although control is then not as fine.
This article explains a little about the principles of feedforward in a control system, albeit an industrial process. The concept is similar for a CH system of this type.
http://www.pc-education.mcmaster.ca/Lecture_Slides/Chap_15_Marlin_2002.pdf
There's an optional bullet type sensor for DHW cylinders which goes into a pocket in the cylinder. This hooks directly to the boiler, allowing it to sense water temperature directly rather than from an on off thermostat. This allows it to detect rate of change of temperature among other things. For example if the set point is 60 degrees and I am just drawing off little bits of water, the boiler ignores it until the temperature reaches 55 degrees, at which point it fires up and does a water reheat cycle at full power, cylinder only. If I run a shower or draw a bath, it sees a rapid drop in temperature and responds more quickly. There is also a mechanism whereby the boiler begins to throttle back as the set point is approached so that it doesn't overshoot.
The manufacturer even supplies optional PC software so that you can log its every move and even display temperature, power level etc graphs should you be so minded. I take the data from mine and use it for energy consumption recording among other things.
For the CM67, have a look at this application note.
http://content.honeywell.com/uk/homes/files/pag106.pdf
It rather looks as though the outside sensor is there to display temperature on the room thermostat as opposed to taking it into account for control purposes. It may be worth asking Honeywell though.
As regards sharing the clock module, I think it will depend on how it interfaces with the rest of the logic of the controller. If the module simply outputs the time based on the MSF signal (which it could) then it may work. OTOH, if the main microprocessor has to program the chip in the time module or send commands to tell the chip to provide the time then it probably won't work to drive multiple controllers from one time module.
.andy
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If
rads
If you are having TRVs on all rads (check with the boiler instructions that you can do this), dispense with the wall stat. Install a Grundfoss Alpha variable speed pump which are notably quieter than the old pumps as they match their power to the heating load and flow especially if you have TRVs. The regs say you must have a "control interlock" that cuts out the burner when the house does not require heating. This can be done by having a flow switch on the return pipe. If the TVRs all close down the pump switches itself, the flowswitch say no flow and the burners is off too. One TVR opens up and the pump switches on, the flow switch detects flow and the burner lights.
The boiler may require a minimum flow through the heat exchanger. Insert a by-pass with a gate valve in it from the flow to the return after the pump. With all rads off the valve must be set to give minimum flow through the boiler. The flow switch must be before the by-pass tee on the return. Boiler -> return pipe -> by-pass tee -> flowswitch.
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You are a complete numpty.
Building regs require that you have a room thermostat and at least TRV's on all radiators in sleeping areas (of course you can have more). They also state quite clearly that the use or TRV's alone are not sufficient.
You are required to comply with the building regs if you make any changes to your heating system to bring it up to standard.
Do you regularly fit systems like this? If so, the BCO would be very interested I'm sure.
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Actually, much as I hate to say it, IMM is correct here.
The regulations don't specify that TRVs are used at all. The requirements are that the rooms are individually controlled, which could be TRVs or a separate zone with room programmer/thermostat.

The regulations state that boiler interlock is required. Although traditionally done using a room thermostat that controls the boiler directly, it is not a requirement to do it this way. A flow switch on an automatic bypass loop, for example, is perfectly adequete and compliant to turn the boiler off when all the TRVs close.
Obviously, TRVs alone are not enough, as you say. However, TRVs with a bypass loop and flow switch are. As long as the boiler switches off when the heating load is satisfied, the building regulations requirement is met.
Some quotes of Approved Document L1:
1.38
Temperature control could be effected by room thermostats and/or thermostatic radiator valves or any other suitable temperature sensing devices, together with appropriate control devices.
1.41 (b) Where it is proposed to effect control by thermostatic radiator valves, a room thermostat (or other device such as a flow switch) should also be provided to switch off the boiler when there is no demand for heating or hot water.
Christian.
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Gotcha. Mis-read the documentation I had (slightly) - my source didn't have the line on 'flow switch'. I stand corrected, and promise to check the source document in future and not something second hand.
Now I have a question - Maybe not in the regs, but I thought it was considered 'best practice' to have the mix I went for - TRV's in some places, and a room thermostat for overall control (along with a conventional timer). And preferably a programmable stat. I just can't find the reference for that information ATM.
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a
hot
The best is what I explained. Individual control in all rooms and a flow switch to act the "interlock". The regs state "or other device such as a flow switch". "Any other device" are the key words.
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Not the best of course, but cheap and effective individual control in each room. The best will be complicated and expensive.

This is true, but expensive and more complexity.

A CM67 and zone valve for each room? Nice but expensive.

Very expensive as a controller will be required to mosulate the TVR valve, and then a timer for that room too. Ouch!

That is why you use an Alpha pump.

You are delving into the realms of commercial systems, where say a large conference room would have its own controls. In a domestic house? Not likely.
The cheapest and more practical is what is suggested: Alpha pump, by-pass, flowswitch and TRVs all around. Then split the system into two zones, probably up and down, using a stat/programmer in each zone and one zone valve. Cheap, easy, simple, economical to run and will satisfy most peoples needs.
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Obviously, the system would have been overspecified, but it was an example of the "best" rather than "best value". The system I'm just doing myself will be converted to up and down zones with a 2 port valve and programmable controller each in the lounge and master bedroom. The other rooms will have to fend for themselves on TRVs.
A system like that is pretty cheap, easy to install (or even modify an existing system to) and allows separate timing for the sleeping and living room areas as a whole, which is quite an advantage when the time usage profiles are so different between the two. The differences between 2 bedrooms, though, aren't quite so great, so might not justify the provision of additional zoning.
BTW, how does the Alpha know when to restart? Does it "poll" at a certain frequency to check the resistance?
Christian.
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Best, yes. Over engineered, probably yeas for an average home.

I did this 10 years ago for a relative, except they had the downstairs stat in the hall, which acted more as a high limit rather than a comfort control. The upsairs is only on in tgemmornings and evenings, and if heat is wanted outside these times, just flick the override switch. Now I would have two simple timers for each zone, TVRs all around and an Alpha.

The pipework to split the system may be quite a task in some homes.

The one I did saved about 20-30% in fuel. It was a big house, so made all the difference. having two separate zones is a cheap undertaking, yet saves more than fitting a condensing boiler.

It starts up occasionally to detect the pressure. On start up they can make a stammering sound. This is normal as it judders by switching off and on to dislodge any debris in the pipework.
A normal pump can be used except that a timer would have to be activated to turn the pump when the flowswitch cuts out. A cheap one can got from RS, Maplin, etc, and some thought into the operation and wiring. using an Alpha and flowswitch is simple and easy.
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