Correct flow rates for UFH?

[Chriswills]

@PeterW any updates on this topic?

 

Now due to the temp drop this week, my consumption has gone to 113kw in a 24 hour period so eager to sort the weather compensation if it helps reduce. Or something else. 
 

@PeterW need your help

please. 

[PeterW]

So this sounds like a fairly large house and the energy calculation for SAP shows pretty poor by modern standard of insulation. Even if you said SAP was correct, and 75kW/m was the heat requirement then if you average this across the heat months I would I expect that 113kW in a day isn’t that unreasonable in really cold weather for a house from 2009 with a floor area of 248sqm. At a CoP of 2 you are using 220kW heat or losing 10kW per hour, and that’s not unreasonable given the construction standard. 
 

@A_L any thoughts on this ..? 

[Chriswills]

Can’t understand how the rating reflects the build standard as I project managed this house together with building regs personnel and I personally rock wooled and insulated every single area inside the house. All the outside was cavity with k rendered block walls, insulation boards, thermo blocks, dry walled and skimmed. 
 

if the heat pump ever packs in, I will never replace it and go gas instead. They just can’t warm up enough in the cold so what’s the point of them really. Huge expense for a huge cost in electricity and no way is it a saver. At least gas is not affected directly by cold. 
Sorry, rant over 

Edited January 24, 2021 by Chriswills

[Chriswills]

@PeterW is it worth playing with the temp compensation settings?

Last 24 hours I used the timer to knock it off at midnight and back in at 5am that gives us 74kw. Better ?

[PeterW]

3 hours ago, Chriswills said:

Can’t understand how the rating reflects the build standard as I project managed this house together with building regs personnel and I personally rock wooled and insulated every single area inside the house. All the outside was cavity with k rendered block walls, insulation boards, thermo blocks, dry walled and skimmed. 

But if you used 100/100/100 wall build up with only rock wool in the cavity, and only 80mm of insulation under the floor you met the Regs at the time. And the rating will reflect that. The numbers in the report are far higher than current Part L standards. Did it have a blower test done ..?

[ProDave]

3 hours ago, Chriswills said:

Can’t understand how the rating reflects the build standard as I project managed this house together with building regs personnel and I personally rock wooled and insulated every single area inside the house. All the outside was cavity with k rendered block walls, insulation boards, thermo blocks, dry walled and skimmed. 
 

if the heat pump ever packs in, I will never replace it and go gas instead. They just can’t warm up enough in the cold so what’s the point of them really. Huge expense for a huge cost in electricity and no way is it a saver. At least gas is not affected directly by cold. 
Sorry, rant over 

A heat pump will never get down to the cost of mains gas but in ideal conditions it will get close. By hoping they will you are missing the point.  I bet a replacement gas boiler would still result in what I would consider expensive heating, even if it was lower than the present cost of the heat pump.

 

For most of us a heat pump made sense for a low energy well insulated house, where mains gas is not available, and a heat pump gives probably the cheapest heating available for this particular house.

 

And there is the small matter of greenhouse gasses that should be less with a heat pump and improving all the time as more f the grid electricity comes from renewables.

[SteamyTea]

CoP is Coefficient of Performance.

It is just the term used to express the difference between Energy In to Energy Out.

So a real fire may have a CoP of 0.25, a car engine 0.27, a normal gas boiler 0.70, an electric immersion heater is 1. Heat pumps range from just under 1 to about 5, depending on the temperatures involved.

[A_L]

8 hours ago, PeterW said:

any thoughts on this ..? 

 

IMHO there are too many unknown variables to be confident about this. Particularly infiltration rate and use/heating of third floor.

[Chriswills]

38 minutes ago, A_L said:

 

IMHO there are too many unknown variables to be confident about this. Particularly infiltration rate and use/heating of third floor.

Third floor is as and when. It’s a movie room so has occasional use. First floor rads on from 7am to midnight albeit only 4 of them. I hate rads in y bedroom and never use them and ufh 24/7 although I’m getting better results on electricity by switching off from 12 until 5am. House is still warm when we get up and saves about 30kw. 

[Chriswills]

@PeterW do you think it’s worth trying weather compensation settings again?

[PeterW]

Depends. What are you trying to achieve ..?? Is it that the cost of heating is excessive ..??

One of the issues here will be the building fabric so without increasing insulation levels or decreasing losses through draughts etc, you sill be chasing ever reducing opportunities. The other issue is if you take the flow temps above 40°C you will hit the CoP and that’s not a new ASHP it’s unlikely to be inverter driven so will use more power. I would put it back into the auto setting it was on previously and monitor for 72 hours - then compare and see if you have used more or less (given the temperatures this week are meant to be pretty static)

[Chriswills]

@PeterW I’m around 74kw now when I switch the UFH pump off from 12 until 5 in the morning as opposed to 113kw leaving it on 24/7. We pay £0.1155 a KW so over a month that way it saves about £140. 
Temps are -3 here in the morning so I’m keeping a daily log on usage. 
I did try your previous advice on temp compensation settings but the return flow went too low, can you advise on settings to keep my return flow at 37 please and I will try it out

[Mr Punter]

On a slight point of pedantry, I do not find it easy to understand technical terms and measurements but I find it even more confusing when I keep reading the wrong units.  It is like frequently reading a misspelt word.

 

kW is a measure of power.

 

kWh is the measure of energy.  It is the unit used by most energy companies.  1 kWh = 1 kW for 1 hour, 10kW for 6 minutes etc.

[SteamyTea]

Or

A watt is a joule per second. J.s-¹.

3,600,000 J is 1 kWh.

 

 Joule is the SI unit of energy, not the kWh.

I think we should ditch the kills wot our and go for mega joule.

 

 

[ProDave]

It's "return flow" that confused me.

 

It's the flow temperature that is usually of interest and the one that is controlled.  Return temperature is what it is and may be of interest to note, but it is not the one usually controlled.

[Chriswills]

44 minutes ago, ProDave said:

It's "return flow" that confused me.

 

It's the flow temperature that is usually of interest and the one that is controlled.  Return temperature is what it is and may be of interest to note, but it is not the one usually controlled.

It is on this unit but I can read the flow too. So for example I set the return to 37 and the flow will read 40. Always a 3 degree delta. 
The input is always entered by selecting return temp. 

[Chriswills]

3 hours ago, Chriswills said:

It is on this unit but I can read the flow too. So for example I set the return to 37 and the flow will read 40. Always a 3 degree delta. 
The input is always entered by selecting return temp. 

What do you reckon @ProDave?

[ProDave]

50 minutes ago, Chriswills said:

What do you reckon @ProDave?

I have never encountered one like that.  Why would you want to control the return temperature?  usually you set the flow temperature and the return will be a bit lower.

[Chriswills]

@ProDave here’s the instructions. The delta to flow is plus 5 deg or supposed to be.  
Mine is set at 37 and when the return of the pump temp drops to 34 it switches on again until reaching the return of 37 and so on. 

 

 

 

[SteamyTea]

1 hour ago, ProDave said:

Why would you want to control the return temperature

Does seem odd.

Taking a trivial example:

4.2 [kJ.kg^-1.K^-1] x 2 [kg.s^-1] x 5 [K] = 4.2 kJ.s^-1 = 4.2 kW.

 

Would make the flow of the system critical in delivering power.

[Chriswills]

2 hours ago, SteamyTea said:

Does seem odd.

Taking a trivial example:

4.2 [kJ.kg^-1.K^-1] x 2 [kg.s^-1] x 5 [K] = 4.2 kJ.s^-1 = 4.2 kW.

 

Would make the flow of the system critical in delivering power.

Just the way it is I guess. 
 

What I need is some revised temp compensation settings to try. @PeterW
 

ATM leaving off overnight is saving me a lot of cash and heating not too bad either. It’s never going to be great I guess in this weather. 

Edited January 25, 2021 by Chriswills

[Chriswills]

@PeterW hello again. 
now this cold spell has hit, I have had to turn my temp on the ashp up to 42 from 37 as house is too cold and rads almost Luke warm at best. Now using 67 kw a day compared to about 50 kw in January. 
would like to try the weather compensation settings again. Can you help please ?

[dpmiller]

On 25/01/2021 at 17:46, ProDave said:

I have never encountered one like that.  Why would you want to control the return temperature?  usually you set the flow temperature and the return will be a bit lower.

 

the default setup on my ASHP was return temp too, but "return" in this case is a wandering probe that could instead be in a buffer tank. I've now re-set it to flow to try. Power consumption seems very similar in both modes.

 

In both cases my external probes tell me that return temp pretty much matches the circulating temp in the slab, but the delta and pump speed control are radically different. Tis velly interresting. I'm waiting for a flow-setter coming so I can get the pump speed best optimised. It's PWM but the limits are adjustable, plus I've got a secondary in the plant room too.

[Chriswills]

10 minutes ago, dpmiller said:

 

the default setup on my ASHP was return temp too, but "return" in this case is a wandering probe that could instead be in a buffer tank. I've now re-set it to flow to try. Power consumption seems very similar in both modes.

 

In both cases my external probes tell me that return temp pretty much matches the circulating temp in the slab, but the delta and pump speed control are radically different. Tis velly interresting. I'm waiting for a flow-setter coming so I can get the pump speed best optimised. It's PWM but the limits are adjustable, plus I've got a secondary in the plant room too.

GOT YOU...that could be an issue for me, as we have nothing coming from the ASHP to buffer to tell it anything. Maybe weather comp is my only hope here.

[ProDave]

The "issue" I have with this ASHP having the return as the set point, is it then maintains +5 for the flow temperature.

 

I have observed with mine when only one UFH loop is on, there is very little difference between the flow and return, perhaps 2 degrees or even less.  So I would never achieve the 5 degrees it wants and I would end up running with the flow temperature hotter than I want, by which time the return temperature would overshoot it's target.

 

But it is the way the manufacturer has designed it so you have to work with it.