What size boiler needed

[sherylryan]

Out

Yes, it's working as I thought it might, apart from temp 1 at 60C which should be the same as the boiler flow at 76.5C or vica versa. The TMV is controlling (first mixing) the temp at 48C = temp 5, this is then (second) mixing with the manifold return of 34C to give a final mixed manifold temperature of 38C, there is only a dT of 4C across the loops so do your calc, LPM*60*dT/860, to give the loop output, kw.
The TMV mixed flow temp of 48C is returning to the boiler which is very good from a balanced corrosion and efficiency point of view, obviously if you require the manifold flow temp of 38c increased then you have to increase the TMV setting.

Its quite a clever control system IMO especially for a oil fired system as it obviates the need for recirculation if the manifold return was returned to the boiler.

Yes I can’t work out why the flow temp at 1 isn’t the same as the boiler. Output of 4.1kw.

It’s a shame the kitchen manifold doesn’t run like this. I ran it after this manifold and could not even get the flow temp out of boiler up to 55, but yet this got to 76.5 at boiler

Another thing I noticed today, if you reduce the pressure on the pump while radiators are calling for heat the flow temp rises and so does the return temp.

But if you reduce the pump pressure when the UFH is calling the flow temp rises and the return temp drops.

 

[ShaunCorbs]

Heatloss on pipework?

 

[sherylryan]

Heatloss on pipework?

Yes possibly. should the pump be set to flow rate instead of constant pressure?

 

[John.g]

A headscratcher Shaun, the return from the manifold to the boiler is a measured 46C (but is possibly 47C/48C) and its 46.3C measured at the boiler so very little loss in this pipework. The heat loss based on 76.5C/60C and a boiler flow of ~ 4.2LPM = loss of 4.57kw, no way IMO. (Boiler flow 76.C measured at the boiler, 60C measured at the manifold)

 

[ShaunCorbs]

Yes possibly. should the pump be set to flow rate instead of constant pressure?

Problem with setting it as flow is that’s ok if you have no controls and the load is matched eg your Heatloss is the same as your rads/ufh

But as you have multiple zones and on off controls I would leave it on pressure

The other way to do it is temp difference but you require a sensor if the pump is capable

 

[ShaunCorbs]

Op can you go round and when the system is on measure all of the flows and see if there’s any difference in temp etc ?

 

[sherylryan]

A headscratcher Shaun, the return from the manifold to the boiler is a measured 46C (but is possibly 47C/48C) and its 46.3C measured at the boiler so very little loss in this pipework. The heat loss based on 76.5C/60C and a boiler flow of ~ 4.2LPM = loss of 4.57kw, no way IMO. (Boiler flow 76.C measured at the boiler, 60C measured at the manifold)

Very confusing, I believe something is happening inside the boiler as the setpoint was 65 degrees but the flow leaving the boiler is high.

Flow gets well above setpoint with laundry UFH & Rads

Flow does not reach set point for Kitchen ufh manifold.

 

[ShaunCorbs]

If you press the right arrow on the pump should show the flow rate

 

[John.g]

I get 21kw providing your lpm is correct

Also ufh is a dt 7 not 12

Very confusing, I believe something is happening inside the boiler as the setpoint was 65 degrees but the flow leaving the boiler is high.

Flow gets well above setpoint with laundry UFH & Rads

Flow does not reach set point for Kitchen ufh manifold.

Can't show calcs just now but 60C does tally with manifold flow and temps, try and measure that 76.5C boiler temp as far away on the pipe as you can but before any T off to anywhere, the only way that it's a tue temperature is if the boiler is cycling rapidly but with the off time way longer than the on time, the temp will then certainly reach very high temps especially if no pump overrun installed. The boiler circ rate at 4.1kw manifold requirement will mean/should result in a lot of cycling especially with a boiler flow rate of less than 5LPM.

 

[sherylryan]

If you press the right arrow on the pump should show the flow rate

I tried to find it the other day but I’ll get the instruction manual out and have a look.

 

[sherylryan]

Can't show calcs just now but 60C does tally with manifold flow and temps, try and measure that 76.5C boiler temp as far away on the pipe as you can but before any T off to anywhere, the only way that it's a tue temperature is if the boiler is cycling rapidly but with the off time way longer than the on time, the temp will then certainly reach very high temps especially if no pump overrun installed. The boiler circ rate at 4.1kw manifold requirement will mean/should result in a lot of cycling especially with a boiler flow rate of less than 5LPM.

Ok, I’ll move the thermostat to the flow pipe before it tees of into the valves for UFH manifolds. Thank you.

 

[sherylryan]

Can't show calcs just now but 60C does tally with manifold flow and temps, try and measure that 76.5C boiler temp as far away on the pipe as you can but before any T off to anywhere, the only way that it's a tue temperature is if the boiler is cycling rapidly but with the off time way longer than the on time, the temp will then certainly reach very high temps especially if no pump overrun installed. The boiler circ rate at 4.1kw manifold requirement will mean/should result in a lot of cycling especially with a boiler flow rate of less than 5LPM.

So I ran the boiler and watch, flow directly out the back of the boiler 75 degrees on 2 different thermometers, temperature before 2 way valve for UFH manifold was 60 degrees.

This could possible explain the short cycling and the boiler re firing again when the flow water is still reading 66 degrees at the boiler.

I also ran the same experiment with the Kitchen manifold, flow temperature directly out of the boiler 54 degrees, flow temperature before 2 way valve for ufh manifold was 54 degrees. Never reached boiler setpoint.

 

[John.g]

Boiler not cutting out on kitchen manifold probably because heat demand greater than boiler output?

When boiler cycles on laundry manifold the circ pump should continue to run continuously even when the burner cuts out and should only stop when room stat shuts the boiler down, check this out, also monitor boiler temp while burner off and note the temperature that it cuts in at again, should normally be a 10 deg hysteresis before cut in, my 20kw Firebird has 10/12 deg.

 

[John.g]

Also check boiler return temp when burner cuts back in but I think you have posted trends on this previously?

 

[sherylryan]

Boiler not cutting out on kitchen manifold probably because heat demand greater than boiler output?

When boiler cycles on laundry manifold the circ pump should continue to run continuously even when the burner cuts out and should only stop when room stat shuts the boiler down, check this out, also monitor boiler temp while burner off and note the temperature that it cuts in at again, should normally be a 10 deg hysteresis before cut in, my 20kw Firebird has 10/12 deg.

Yes circ pump continues when boiler cuts out and stops when room starts reaches temperature.

When the boiler is off the temp on return rises and flow drops and boiler cuts in again when flow temp is 66/67 degrees. Return temp is 57 degrees.