Balancing a separate Conservatory heating zone

[Mary Hinge]

Just replaced an ancient 30KW Kingfisher II floor-standing lump with a shiny new GlowWorm HXI 30KW condensor (credit due to IMM believe it or not for

tip, saved £££s thanks).

The house is a large, Edwardian detached job with four big bedrooms. Before replacing the boiler I did an approx size of all the rads and came up with 27KW needed if you allow ~3.3KW for the HW cylinder, and therefore went for a 30KW boiler. I also had the pump and S-Plan control valves replaced as they were rather old, and took the oppurtuinity to put the conservatory on a separate zone. The new pump is an Alpha 15/60 (currently set to constant head setting as there is a bypass).

The conservatory has two 3.3KW Double-panel convectors, and a 600W single-panel convector. There is also 500W single-panel convector in the bog adjacent to the conservatory, which will eventually be moved back to the main rad zone (couldn't move it without ripping floor up so it will have to wait a while).

One thing I've found is that it seems impossible to get a 20 degree C drop across the conservatory rads when only that zone is calling for heat. If you shut down the lockshields the boiler seems to get insufficient flow, heats up really quickly in a couple of mins then shuts down. Opening up the lockshields fully to increase flow seems to suit the boiler more, and you do seem to get a bit more of a temperature drop across the two big rads (approx 10 degrees). Closing down the smaller rads doesn't really seem to acheive much as the flow across the boiler drops and the temperature drop across the big rads actually drops to virtually nothing, without actually increasing the temp drop on the smaller rads.

One advantage of the low temp drop in this zone is the conservatory heats up pretty quickly; I would guess the downside is less efficiency in the boiler due to the high return temperature. Once the circuit has heated up the boiler cuts out at about 70 degrees, drops to about 60 degrees then cuts in again for a couple of mins or so.

Can you confirm this behaviour is to be expected? Any comments/observations?

TIA,

MH

[Christian McArdle]

Personally I wouldn't worry about it. Sounds like the pump is going too fast when there is only conservatory load. TBH, this won't be a common case, as the house zone will often be calling for heat too.

As you say, the radiators are well oversized and cause the conservatory to heat up rapidly, so the slightly increased return temp will only apply for a short period (10 minutes you suggest). Additional energy savings to be had by reducing this the return temp for such a short period are very marginal.

Christian.

[Phil Addison]

Yes, it's a shame he spoils what good advice he has by the arrogant and insulting nature of the majority of his posts. It means that any useful advice he has can get lost in the welter of trivia.

I have not used that pump, but I'm sure Andy Hall will be able to advise on its best settings.

Well yes - shutting down LSVs does reduce the flow. 7.4kW is a significant load and will need a decent flow rate to transfer that heat from the boiler to the rads. You need to wait quite a long time after throttling the LSV down to allow the rad too cool - are you waiting long enough? Also if the rads are oversized you will want to throttle them down to a *larger* temp drop than normal or the room will overheat. Don't forget that a larger drop corresponds to *less* heat output because the average surface temperature is reduced.

Confirms the above. With 10C or so across them they will be delivering their full rated output.

What do you mean by "the flow across the boiler drops"?

It sounds as though you initially had the small rads LSV wide open thus bypassing the big rads. When you closed the small ones down, the big ones were then able to get a decent flow. I think you need to re-read the FAQ, as following it should sort all this out.

Do you ever want to run both zones together? If so you need to do the balancing in that mode.

Please take special note of the Principle section of the Balancing FAQ, especially 2nd paragraph, regarding not being able to get a specific temperature drop across rads.

It should not do that with a heat load of over 7kW. Lack of balance is a likely cause. Also, adding extra rads may mean re-balancing the rest of the house, depending on pipe layout. You should have one, and only one, rad with its LSV wide open.

No.

Read

and come back if you have more questions.

Phil The uk.d-i-y FAQ is at

NOSPAM from address to email me

[Mary Hinge]

Firstly I got my sums wrong, the two large rads are around 1.7 KW each, so around 3.4KW *in total*. D'oh! Yes I waited for the system to fully cool before attemping balancing. Note that the conservatory is quite large, the heatloss program suggests 4.8KW is required, currently we have around 4KW in total so if anything slightly undersized. The room overheating is not possible as the conservatory is a completely independent zone with it's own thermostat.

I get the impression that not enough water seems to be going through it so it cannot modulate down low enough (the manual states a minimum flow of 1300 litres/hour).

In practice they don't seem to come on together very often. A lot of the main house zone pipework is 1 inch with a lot of rads hanging off of it, and doesn't seem to have much flow resistance so when both zones are on it doesn't seem to affect the main house. The conservatory zone is all in 15mm so has more flow resistance.

As stated above I made an error in my original statement; the total load is around 4.5KW

Thanks,

MH

[Phil Addison]

Just a quick reply to this bit - I'll digest the rest of your post later.

This 1 inch pipework sounds like a "single-pipe" system. This is an old and discredited system for domestic properties and the balancing FAQ process will not work with it. Is there a single 1" pipe passing under each radiator, with both the flow and return of the rad connected to it? Do you have calipers to check the diameter, because the old pipes were

1" *internal* diameter whereas modern ones are 22mm *outside* diameter? I don't have the o/d of imperial pipes handy, but you could have 3/4" i/d which has an o/d close to modern 22mm pipe.

If I am right about this, it could be that the pump is inadequate for the new zone that you have, which presumably uses two separate 15mm flow and return pipes. Can you see a make/model label on the pump?

Phil The uk.d-i-y FAQ is at

NOSPAM from address to email me

[Mary Hinge]

Definately not a single-pipe system. The 28mm feeds the main CH zone (upstairs and downstairs rads) with separate flow and return, I suspect it probably drops down to 22mm somewhere under the ground floor after the 22mm flow and return for the upstairs rads splits off.

The pump is a brand new Grundfos Alpha 15-60 and yes as stated the conservatory zone is all 15mm. You might need to re-read my original post for more background.

Thanks,

MH

[Phil Addison]

Oops, yes forgot that - I remembered the Edwardian bit and mention of some things being old. So basically, its back to what i said before: You need to balance it properly before we can do anymore diagnoses. With the info to date it appears to be an out of balance system, which is common for a new installation - most plumbers just do not understand balancing and either don't attempt it or don't achieve it.

You haven't yet said the make/model of the boiler, but assuming it is a modulating one, at 30kW rating it may not modulate down to 3.4kW so you may have to expect it to cycling on off to a degree.

Summarising the balance process, you put the pump on max, open all the rad valves (LSVs, TRVs, or hand valves) and allow it to heat up. Normally at least one rad will have a cooler return. Ignore those, and go to the ones with very hot returns and start shutting down their LSVs. That will send a greater flow to the cool ones which will show an increased return temperature. Keep repeating this procedure until all returns are very hot. Ideally use an IR thermometer to evaluate the actual return temperature - it makes it easier. Don't try to get a specific temperature drop, just get them all about the same.

If you can achieve that, then you can think about adjusting the pump.

Phil The uk.d-i-y FAQ is at

NOSPAM from address to email me