Tuning CH

[Kostas Kavoussanakis]

I am not sure what I want to do counts as balancing and if it is subject to the balancing section of the FAQ. Balancing looks fiddly to me and back-breaking is not required, I have done this already. :-) So I am hoping for a simpler solution.

The problem is my (largish, remote from the boiler and adjacent to an unheated sun-lounge) lounge lags 1-1.5C from the hall. The hall is heated by the only non-TRVed radiator in the house, as it also hosts my new Honeywell CM907 thermostat.

Because the rest of the house has TRVs, I can just raise the CM907 to

22.5, so the lounge reaches 21-21.5, but I don't see the benefit of boiling the hall. I have done this, so as to test it's possible for the lounge rads to heat the lounge to the desired temp. In case it matters, I note that the thermostatic valves in the lounge are the only ones left in the house that have the TRVs fitted at the wrong side of the rads. For the past 23 years that the house has been up :-(

I have checked that the lounge lockshields are fully open. I am now thinking of restricting flow to the hall radiator (remember it is the bypass rad, no TRV). Is this a good idea? Which side do I restrict, the in or the out?

And while I am at it, I have an encyclopaedic question: does the fact that one has TRVs mean that, because a room that's before another reaches the TRV shutdown temp, it can cut out others after it in the circuit? Or are rads not really in line?

Many thanks in advance for any answers,

Kostas

[Ed Sirett]

If the valves do not bang, chatter, or groan then you are fortunate and there is no problem.

It is possible (but unlikely) that the hall is the bypass (you'll need to find out what you have. See FAQs and wiki. Y-plan or S-plan ? combi or non-combi? etc.

Otherwise turning the hall radiator down is a good move, perhaps even off altogether if the hall gets enough heat from elsewhere?

It makes little difference whether you restrict the in or the out. Do the side that is harder to tamper with.

Almost certainly the rads are not in line (known as a one pipe system) instead they are all in parallel with each other. One pipe systems are sometimes found in older larger public/commercial installations.

The effect of the TRVs is to help balance the system for you but it helps a lot if the system is already pretty good without their help.

[Tim Lamb]

In message , Ed Sirett writes

Yes:-)

It is time (cold last night) that I re-visit a similar problem here.

Largish system, 100,000 BTU boiler, 3 speed youngish Grundfoss pump, TRVs throughout apart from 2 bathroom rads, plus a retro-fit wall stat!

Unfortunately the wall stat. is fitted too close to the kitchen and responds to cooking activity leaving remote parts of the house too cold. The other problem is that, on full speed, the system howls during the boiler overrun time.

There was some comment in here about fitting modulating pumps and I wondered how this would work. Presumably, without the wall stat. the boiler would maintain the pipework and the two by-pass rads at boiler temperature?

regards

>

[Kostas Kavoussanakis]

Thanks Ed,

Some comments (and further questi> >> The problem is my (largish, remote from the boiler and adjacent to

All the other rads have TRVs; doesn't that make it de-facto the bypass rad? I know it's a non-combi (Potterton Netaheat). I had a look at the FAQ (nice descriptions, thanks) but I could not find a way for the layman to deduce what set-up they have. Is there such a thing?

Does "otherwise" here mean that if I have a specific set-up, restricting it is a bad idea? What set-up would that be? I am *not* going to shut this rad down completely; I depend on it as a bypass, as I said.

Thanks for all the other answers!

Kostas

[Ed Sirett]

A (correctly set up) smart by pass would probably solve the howling problems.

[Ed Sirett]

A radiator which can not (easily) be turned off provided a path for water to circulate on a Y-plan system.

If you have an S-plan then you will have/may need a bypass provided elsewhere. Although a Netaheat has a cast iron heat exchanger and probably does not require any bypass.

You probably don't need this rad as a bypass but without knowing the exact details of the system I can't really say. I SUSPECT that you don't need to keep this radiator open.

[Tim Lamb]

In message , Ed Sirett writes

So what is a smart by pass?

regards

[Ed Sirett]

A pressure sensitive valve which allows water to flow when there is sufficient differential pressure between the inlet an outlet ports. The pressure is adjustable (educated guess work required). I'd installed it, screw it to the highest setting and then if there is any howling I'd start to open it until the howling stops. Hopefully the heating will operate as before minus the "wolf" stuff.

E.g

[Tim Lamb]

In message , Ed Sirett writes

Moving the thermostat away from the kitchen door is also do-able but I would like to try the system as it was intended to run: on TRV's alone. In a rather rambling house with lots of exterior walls, a central thermostat is never going to give good control in all weather conditions.

regards

[Mike Clarke]

Similar situation here, on a sunny day in mid winter the rooms at the front can be up to 70 F without any heating while it's only 60 F elsewhere in the house. A wired room stat in one of the back rooms won't do because there's some days when we may not be using that room so the rad would be shut off. We've got TRVs throughout which do a reasonable job but the boiler spends a lot of time short cycling, I'm contemplating adding a Honeywell CM927 wireless stat so we can move it around as needed.

[Kostas Kavoussanakis]

Room thermostats should be in areas unaffected by drafts and where there is no TRV to confuse them.

FWIW, I replaced my old Honeywell thermostat with the CM907 and found that it short cycles *a lot*, esp. compared with the previous stat. I am guessing this is a result of the algorithm it uses to keep temperature steady.

Kostas p.s.: Ed, thanks for the repeated answers to my queries.

[Ed Sirett]

and yet where they eventually receive heat from the heating system in a general sense. what's more it would be good if they were in a convenient position to control.

[Mike Clarke]

But in my current setup there's no room thermostat to turn the boiler off at all so when all the TRVs have decided that things are warm and cosy the boiler still continues to pump hot water through the pipework and the one bypass radiator in the bathroom. This results in lots of unwanted short cycling.

[Tim Lamb]

In message , Mike Clarke writes

Presumably only the pipework feeding the bypass radiator?

I have been wondering about this. How significant is short cycling in terms of boiler efficiency? The *waste* heat from the pipework is still contributing to overall home heating and perhaps leads to some TRV's being set lower than otherwise.

I suppose it is only a real problem where the bypass is a radiator.

A pressure switch could perhaps detect the closure of the last TRV but what would you do with the information? Drop the boiler thermostat setting?

No amount of fine tuning is going to convince the housewife that the central heating is *on* if the radiators are not actually hot!

regards

>

[Mike Clarke]

In our case it's probably quite significant. When once the house has warmed up in the morning it doesn't need much heat to keep the temperature through the day. The timer only has 2 on/off cycles per day so it comes on for the morning and late evening. Through the day we turn it on manually for a few short top-ups of about 30 minutes to 1 hour as required. If we leave it on all the time and rely on the TRVs then the boiler frequently cycles on for brief periods, the minimum level that it will modulate down to is 9KW so through the day that would be quite a significant energy burn which is just not needed. A room stat would overcome this and save us the hassle of turning it on and off from time to time. We have no problem going along and turning it on when we start to feel cool but a stat wouldn't forget to turn it off again as we sometimes do and would keep the temperature more steady than we manage to. But, as I said in my earlier post, there's no single location which would be appropriate for all conditions, hence the thoughts of using a "portable" wireless one.

The boiler has an integral bypass but I prefer to let it have a bit of real load too. Even if I relied on just the integral bypass there would still be quite a fair bit of wastage with most of the heat going straight up the flue.

That's the problem, the only override available with our Worcester 350 combi is the connection for a room stat, when this turns off it stops the entire boiler, including the pump, so there's no way of sensing when a TRV has opened again. There are ways of getting round this with a heat exchanger and extra pump, e.g. but probably not worth the disruption and cost.

Another interesting, but expensive, solution is Honeywell CM Zone wireless TRVs but that's about

500 quid on top of the cost of the TRVs to control 6 radiators.

Not just housewives. Lots of people fail to comprehend the concept of thermostats.

[Ed Sirett]

Depends on the boiler type, a modern one with built-in anti-short cycling delay timers will not suffer as much as a natural draught cast iron dinosaur.

When a natural draught boiler cuts on it's internal themrostat it is not doing nothing it is going in reverse you might aswell have a radiator fitted outside.

[Tim Lamb]

In message , Ed Sirett writes

er... confused mode..... does this mean that constantly pumped systems with TRV's are seriously less fuel efficient than a system with a mix of TRV's and a central thermostat controlling the circulating pump?

regards

[Kostas Kavoussanakis]

Understood, but this does not change my initial argument that, if my CM907 behaves in a typical way, adding a CM927 room thermostat will not get rid of short-cycling.

Kostas

[Kostas Kavoussanakis]

All these valid points for a programmable stat, I agree.

Kostas

[Mike Clarke]

I wonder if there'd be anything to be gained by increasing the minimum boiler ON time to 2,3,4 or 5 minutes from the default of 1 minute and reducing the cycles per hour setting? I'm only guessing because I haven't actually had my hands on a CM927 yet, just going by what I see in the installation notes on the Honeywell website.