House temperature rise rate?

[wipeoutdude]

Hi,

Is there a target temperature rise rate for a heating system?

What I mean is that my newly fitted system seems to raise the temperature in the house at about 1C - 1.5C per hour.. Seems a bit slow to me..

So how fast should the heating system increase the temperature if it is spec'ed correctly?

Thanks..

 

[Dan Robinson]

Too many variables.

Emitter size
Flow temperatures
Boiler output
Control regime
Building fabric

 

[D_Hailsham]

Too many variables.

Emitter size
Flow temperatures
Boiler output
Control regime
Building fabric

But it's a newly fitted system. So the installer should have:

1. Taken the building fabric into account when calculating the heat loss.
2. Sized the boiler correctly.
3. Sized the emitters correctly for the desired room temperature taking into account flow/return temperatures
4. Provided a control regime which suits the customer's requirements.

 

[Dan Robinson]

And we have no useful information on any of it. . As per usual.


"new system" for many could just be a new boiler, in the same way "new" can be anything from a few days to a decade.

1 - 1.5 degree an hour.... . From what to what?


Ufh? Rads? Trench heating? Skirting heating? . Furniture blocking the emitters?


Is the boiler set to the correct flow temperature or has someone been fiddling?




Flock knows

 

[wipeoutdude]

Will try give as much info as I can...

New system means completely new from end to end.. So new combi boiler and rads throughout..

House is a 1950s bungalow, filled cavity walls, new double glazing throughout and lots of loft insulation (250mm-300mm)..

Temperature rise is about 1C per hour from ~19-20C to ~21-22C..

Heating flow temp is 70C.. Initially all lock shield valves were wide open.. I have been reducing them gradually to try and get the return temperature below 55C.. Some (bathroom towel warmers) are now only open about 1/8th of a turn and most of the rads are only 1/4 -1/2 turn from closed..

As a side question is it OK to have a the valves closed down that much? or would it be better to reduce the flow temperature and still have the return below 55C??

 

[D_Hailsham]

Heating flow temp is 70C.. Initially all lock shield valves were wide open.. I have been reducing them gradually to try and get the return temperature below 55C.. Some (bathroom towel warmers) are now only open about 1/8th of a turn and most of the rads are only 1/4 -1/2 turn from closed.

A flow of 70C and return of 55C is OK provided the installer took that into account when sizing the rads. But if he assumed the system would be run at the default 75C/65C then the rad output (at 70C/55C) will be nearly 20% less than he expected.

Is it OK to have the valves closed down that much? or would it be better to reduce the flow temperature and still have the return below 55C??

Yes its perfectly OK. Lowering the flow temperature will only reduce the rad output, which is the last thing you want.

 

[Dan Robinson]

I agree with D_Hailsham.

Has the system improved since you did the balancing?

Is the boiler cycling a lot?

How is the by-pass (if any) set?

You still haven't told us what make and model boiler you have and what controller is fitted.

 

[Steelmasons]

my newly fitted system seems to raise the temperature in the house at about 1C - 1.5C per hour.
..

Should've used a different installer.

There is a simple calculation for this.

 

[wipeoutdude]

Boiler is a Worcester Bosch 32 CDI compact that is being controlled by a Siemens RDJ10RF wireless controller..

Boiler is not cycling a lot.. Don't think the balancing made much difference really..

I don't know that there is a bypass.. Is there one built in to the boiler?

So which is the better situation for performance and efficiency?

1) Higher flow temperature and rad valves closed right down to reduce flow enough to achieve 55C or less return.. This means valves open about 1/8th of a turn..

2) Lower flow temperature but with a faster flow through the rads to get 55C or less return..

I guess the only way to improve the system performance would be to add more rads or replace some with larger rads but its probably more cost effective to just have the boiler running hotter and less efficiently..

 

[D_Hailsham]

A bit of homework!

1. Use Baxi Whole House Boiler Size Calculator to find out the heating requirement of your house. (set Hot water allowance in step 3 to 0 as you have a combi.)

2a. If the installer gave you a list of rad sizes & outputs, please provide the info.

or

2b. Use Stelrad Catalogue, page 44 (Elite 50C DeltaT)

3. Post the details

The purpose of balancing is not to obtain a specific return temperature but to ensure that each rad has the correct flow through it.

 

[wipeoutdude]

The whole house calculator says I need 7.6KW..

The sum of all the rads I have according to the stelrad page comes to 9.4KW..

So what does that mean? It's about right?

 

[D_Hailsham]

Sorry for the delay in replying.

The whole house calculator says I need 7.6KW.

And you have a boiler which can supply between 7kW and 24kW. For 95%+ of the time the boiler will only need to supply less than 7kW. which can only be done by the boiler switching on and off, i.e cycling.

The sum of all the rads I have according to the stelrad page comes to 9.4KW.

That figure assumes a 75C flow and 65C return. If used with a 70C flow and 55C return it reduces to 7.5kW and to 8kW for 75C flow, 55C return. As you can see, this gives you very little margin, especially when the external temperature drops below the design value (-1C or -3C).

Now the number of days when it is that cold outside will be very few, say 5% or the year or 18 days. So it might be worthwhile sacrificing a bit of efficiency on those days to ensure the house heats up faster.

The other thing which would help is to reduce the maximum output of the boiler which, as delivered, is 24kW for heating. The boiler will try to provide this but the temperature will rise very quickly as the rads are not capable of using this amount of heat. The boiler will modulate down and go into on/off mode, but the net effect is that the rads will heat up very slowly. If you reduce the max output to say 10kW the cycling effect will be considerably reduced. It's explained in the installation manual, though you might prefer to ask your installer to make the adjustment.

 

[wipeoutdude]

Interesting.. It's all starting to make sense now.. So in effect my rads have been sized for a non-combi boiler that would have a higher flow and return temperature.. By trying to run it at a lower temperature it's not really outputting enough heat, especially at the moment with the colder weather..

This probably also explains what I think is a slow temperature rise in the house..

I haven't noticed the boiler cycling at all.. Seems to just constantly run at a very low rate.. I have looked through the manual and managed to get to the info screens so have good information now..

if I set the flow to 60C (their recommended eco setting) and have all the lock sheild valves wide open I get a return temperature of about 54C.. So I am getting about a 5-6C drop through the system, all rads are getting hot.. According to the info screens the pump is apparently running at 10% (slowest possible) and the boiler is at 30%.. Obviously at this level the rads are very "underpowered" which explains why its running constantly and taking a long time to heat the house..

If I set the flow to 74C the return is about 64C.. Pump is running at 25% and boiler at 40%.. Obviously temperature rises much quicker..

How much less efficient is a combi boiler with a return of 65C vs 55C?

Seems I would have to add quite a few KW of rads to the system in order to run at the lower temperatures but as you say it's only a small number of days in a year that it's really cold so would the cost of the extra rads and installing them be worth it compared to running the boiler at a lower efficiency..

 

[D_Hailsham]

if I set the flow to 60C (their recommended eco setting) and have all the lock shield valves wide open I get a return temperature of about 54C.

The LS valves shouldn't be wide open. They need to be adjusted so the system is correctly balanced, i.e each rad is giving off the expected amount of heat. You may have a 6C drop across the boiler, but it won't be that at every rad.

At 60C flow and 54C return your 9.4kW of rads will be giving off only 6.3kW. Fine if it's 6C outside, but not when it's -1C. Good thing you don't live in Scotland, -13C!!

Do you have an infrared thermometer? If so, use it to check the flow and return pipe temperatures on all rads. (Iif the pipes are unpainted copper, wrap some insulating tape round the pipe and measure the tape temperature.)

 

[wipeoutdude]

Do you have an infrared thermometer? If so, use it to check the flow and return pipe temperatures on all rads. (Iif the pipes are unpainted copper, wrap some insulating tape round the pipe and measure the tape temperature.)

All the rads are getting hot which is what I thought the balancing was for..

So I will use the IR thermometer and then do I just keep closing the lock shield vales down? What return temperature am I aiming for? I know that to get a 20C drop the vales are just about closed.. Like 1/8 - 1/4 turn open..

I think if I was in Scotland I would probably have much bigger rads..