ASHP: lagging pipes in loft

lovesgshp

Gterr
Have all of the upstairs rads got TRV's on them, including the bathroom?
With all the timers etc, then you could be influencing flow rates, as the majority of pumps need to have 70% of all circuits open.
Try what Albyota suggests and see if that has any effect.

gterr

Geotherm wrote: »

Gterr
Have all of the upstairs rads got TRV's on them, including the bathroom?
With all the timers etc, then you could be influencing flow rates, as the majority of pumps need to have 70% of all circuits open.
Try what Albyota suggests and see if that has any effect.

Thanks Albyota and Geotherm,

Yes, crazily all the rads have TRVs - even the bathroom one.
I think it's time to try lowering the heat curve. We can live with cooler radiators. Will try this for two or three days and get back to you. I had already thought of getting an element for the bathroom towel rail rad so we could have it warm in the summer when the rest are off.

It would be easier for my experiments if the outside temp would stay constant, but there you go!

Stay tuned!

lovesgshp

Gterr.
I asked one of our design engineers about what was happening with the radiator system problem and have copied below his reply. Please excuse the errors in his English!

If HP run at too high temperature the problem is the flow when radiators closed. Solutions: keep the radiators always open and install room sensor that correct the heat curve.

If when the radiators are open the heat pump run excessively (a lot of operating hour), the problem is probably too high heat loss.
The HP can't reach the temperature because when the radiators open a lot of cold water go into circulation.
Solutions:
a - if the HP cover the house heat loss the problem is only the peak demand when the radiators open. You can solve keeping the radiators always open or installing an adeguate buffer tank.
b - if the HP don't cover the house heat loss the problem is peak demand but it's not sure that you can solve unless an additional heat system.

I hope my english is comprehensible.
Have a nice day!

gterr

Thanks Geotherm.

I think I understand in principle what the engineer is saying.
We have a (theoretically) well-insulated new-build, and we have a primary store, and the rads are open all the time now, controlled only by time clock.

But it still seems to be a choice between
1. a cosy house and plus too-hot radiators plus high electric bills, and
2. House only just warm enough, some UF zones always asking for heat, and lower bills.

I still have some experimentation to do.
Yesterday I lowered the heat curve, to give a flow temp of about 37 C when outside temp is zero. But now the weather has gone mild again, so flow temp has fallen to about 30 C, and UF zones can't reach target temp.
To add to complexity, we have a southerly wind hitting the end of the house - the opposite end of the house to where the outside temp sensor is mounted. I have responded by lighting the wood burner. Now this will mess up my statistics!

I wonder if I should make the heat curve less steep, that is, less dependent on outside temp. This would be a big departure from the recommendations for use of the Worcester-Bosch heat pumps, but I notice from discussions on this forum that other makes of ASHP are set up with constant, or near-constant flow temps, so maybe not that ridiculous.

Cheers!

lovesgshp

gterr wrote: »

Thanks Geotherm.

I think I understand in principle what the engineer is saying.
We have a (theoretically) well-insulated new-build, and we have a primary store, and the rads are open all the time now, controlled only by time clock.

But it still seems to be a choice between
1. a cosy house and plus too-hot radiators plus high electric bills, and
2. House only just warm enough, some UF zones always asking for heat, and lower bills.

I still have some experimentation to do.
Yesterday I lowered the heat curve, to give a flow temp of about 37 C when outside temp is zero. But now the weather has gone mild again, so flow temp has fallen to about 30 C, and UF zones can't reach target temp.
To add to complexity, we have a southerly wind hitting the end of the house - the opposite end of the house to where the outside temp sensor is mounted. I have responded by lighting the wood burner. Now this will mess up my statistics!

I wonder if I should make the heat curve less steep, that is, less dependent on outside temp. This would be a big departure from the recommendations for use of the Worcester-Bosch heat pumps, but I notice from discussions on this forum that other makes of ASHP are set up with constant, or near-constant flow temps, so maybe not that ridiculous.

Cheers!

Change the flow temp to 45C and give some data from that. You can alter all the flow temperatures, but do not compare data from some discussions on other pumps, as they may be misleading.

gterr

Geotherm wrote: »

Change the flow temp to 45C and give some data from that. You can alter all the flow temperatures, but do not compare data from some discussions on other pumps, as they may be misleading.

You mean a constant flow temp of 45 C for all values of outside temp? This would be too high I think: A constant 35 or 37 would be ample.
Or did you mean adjusting the heat curve in another way?

Cheers.

gterr

Thought you might like to see some real data.

The chart shows how electricity usage correlates with outside temperature. I've also shown the heat curve, set at V=22, H=55 (i.e. when external temp is 20 C the flow temp is 22 C; and when external temp is -20 C the flow temp is 55 C)




Now, my question is: do we use more electricity when it's cold outside because more heat is lost from the house and more elec is needed to generate the heat to replace this,
OR, do we use more leccy when it's cold outside because when it's cold our flow temp is higher, and more energy is required to maintain and use these higher flow temps?

(And I don't like the look of our potential electricity usage if the outside temp were to fall to, say, -10C, or even -5C !!!)

Time for bed.

lovesgshp

gterr wrote: »

You mean a constant flow temp of 45 C for all values of outside temp? This would be too high I think: A constant 35 or 37 would be ample.
Or did you mean adjusting the heat curve in another way?

Cheers.

Hi
I just meant the H value.
Have emailed you the Rego 800 simulator, so you can look at how different settings affect values.

lovesgshp

gterr wrote: »

Thought you might like to see some real data.

The chart shows how electricity usage correlates with outside temperature. I've also shown the heat curve, set at V=22, H=55 (i.e. when external temp is 20 C the flow temp is 22 C; and when external temp is -20 C the flow temp is 55 C)




Now, my question is: do we use more electricity when it's cold outside because more heat is lost from the house and more elec is needed to generate the heat to replace this,
OR, do we use more leccy when it's cold outside because when it's cold our flow temp is higher, and more energy is required to maintain and use these higher flow temps?

(And I don't like the look of our potential electricity usage if the outside temp were to fall to, say, -10C, or even -5C !!!)

Time for bed.

Flow temp is higher as the weather compensation increases the heat output.

gterr

Geotherm wrote: »

Flow temp is higher as the weather compensation increases the heat output.

Yes, I do realise this. But electricity consumption is also correlated with flow temp. So, I need to know how much temp compensation is strictly needed to maintain target temps:

If the curve is too steep then when outside temps fall and flow temp rises the system may be using a higher flow temp than necessary (and maintaining a primary store of water at this higher temp), resulting in unnecessarily high usage of elec.
Also, if the curve is too steep then when outside temps rise, and flow temp decreases, we may end up with a flow temp that is too low to maintain our target temps.

I've been taking meter readings every 12 hours at 9am and 9pm, and with the original heat curve (V=22, H=55) we were using more units between 9pm and 9am than we were in the daytime between 9am and 9pm. Is this because we are losing a heck of a lot of heat from the building, or is it because the system is maintaining a higher-than-needed temp in the primary store?

Our system is complicated by being a mixture of UF coils and rads, each of which really needs a different flow temp. (And then we've got our own idiosyncratic plumbing - lack of bypass valve etc., and timer/stats in every UF zone - which further complicates the issue and probably compromises the economics.)

The thing that stops me making too free with the heat curve is that surely Worcester-Bosch have done no end of research and their recommended heat curves ought to be optimal, and should be better than anything I can do by trial and error and with my lack of preofessional knowledge.

Geotherm: Many thanks for emailing the simulation software for the Rego 800. I will have a look at this this weekend.

Many thanks for your continued interest and support with all this!