Posted by: @grahamf

↑

I am interested to find out whether other people's systems have a similar temperature difference between upstairs and downstairs 

Until I turned down the lsvs upstairs, yes.  No real need to buy frvs, lsvs, or trvs fitted with decorator caps to replace the heads, will do the same, albeit with slightly more fiddling, but it's a once only job.  Having adjusted the bedrooms are slightly cooler than downstairs, which we prefer.

Posted by: @grahamf

↑

We are running our heat pump with weather compensation and a room thermostat set at 20C in the hall

Before fiddling with the upstairs rads I would turn the downstairs thermostat up to 30 and adjust the weather compensation down to get the house temp right.  This should maximise both efficiency and comfort.  

Our arrangement of open doors etc. is very similar to yours but we have a requirement for a slightly higher temperature (22.5 deg. C) and we heat 24/7. I have employed the LSV’s to set the output from some radiators just to even out the room temperatures. On bedroom has a programmable TRV so that we may sleep in a cooler room. All the LSV’s downstairs are fully open and the Homely Mode (temperature probe) is in the living room. The maximum variation between rooms over perhaps a week or more might be 0.4 - 0.5 degrees C. so we find our comfort level to be very stable. We have one exception as we keep the bathroom LSV fully open and enjoy a slightly higher temperature and this we appreciate no end! Regards, Toodles.

We have smart TRVs in the bedrooms set at 20 or 21, but can set back further if required. We are operating under the principle that if used relatively sparingly (16 radiators in total with only 4 having TRVs) it should generally be ok, and this seems to work fine for us.

Fwiw I ried smart trvs with my gas heating.  I found it too much faff to use the smart features so reverted to dumb trvs and subsequently, when I got my ashp, to no trvs.  The most comfortable for me is the last of these, adjusted on the lsvs to be a bit cooler than the rest of the house and then left.  Obviously this will differ from person to person and house to house but, before spending money, try the simplest possible solution.

@benson We have 10 radiators fitted with TRV’s only two are ‘active’ and I am contemplating replacing the other eight with decorator’s caps for neatness. (I blame the MCS for asking installers to fit TRV’s even though they are [in my opinion anyway] more of a source of problems if used extensively than they are of any practical use) Toodles.

Posted by: @grahamf

↑

We all know that hot air rises, so maybe this is just a natural result of convection

Hi @grahamf, yes, exactly this. Unless you live in a house with all internal doors closed, high levels on insulation between downstairs and upstairs, and zero infiltration [air movement] between rooms, you'll get a thermal gradient between low and high elevation. CIBSE and ASHRAE guides have methods of calculating the rate of heat movement due to the natural buoyancy and the lower density of heated air, but to my knowledge, the phenomena is not considered in any heat loss and emitter sizing software. Nor have I seen any consideration of this or suitable correction factors that might be used in CIBSE's domestic heating design guide. CIBSE and Building Regulations assume the two levels are controlled as two zones, so heat can be demanded individually, but despite that being a BR requirement it's not efficient control with low & slow renewable heating where 'open loop' stable system flow rate is best.

It has become a much more prevalent phenomena in recent years due to better thermal insulation performance levels in houses & lower levels of air change in new build or well retrofitted housing stock. If I were to size emitters then for a typical 2 storey domestic dwelling with living space on the ground floor and bedrooms above, I would oversize downstairs by 10% and undersize upstairs by 10%, save for any WCs and bathrooms. Purely empirical 'wetted finger' numbers here, but there's a PHD research paper for some academic heat geek building services engineer on the subject. (They might already be on it...)

@allyfish thanks for your observations.  At the moment, I suspect that my upstairs radiators are receiving too much water flow even without the +/-10% adjustments you suggest.  I have decided to install FRVs upstairs, so that I have a more scientific flow control mechanism.  However, I am not expecting them to make much difference.

Posted by: @grahamf

↑

@allyfish thanks for your observations.  At the moment, I suspect that my upstairs radiators are receiving too much water flow even without the +/-10% adjustments you suggest.  I have decided to install FRVs upstairs, so that I have a more scientific flow control mechanism.  However, I am not expecting them to make much difference.

Why arent you expecting them to make much difference.  If the water flow is shut off completely they wont heat at all, and in principle the flow could be adjusted to be anywhere between that (ie zero) and your current flow rate.  

@jamespa

Posted by: @jamespa

↑

Before fiddling with the upstairs rads I would turn the downstairs thermostat up to 30 and adjust the weather compensation down to get the house temp right.  This should maximise both efficiency and comfort.  

I followed your advice and the room temperature drifted up slightly to around 20.5C, even hitting 20.7C at one point.  I am not sure that this was due to the thermostat temperature increase to 30C, as the very gentle upward trend had been continuing for several days - since we had our roof put back on!  

Anyway, I adjusted the weather compensation Shift down from +2 to +1, the smallest adjustment possible.  The temperature is now tracking 20C closely, without any intervention from the thermostat.  The heat pump turns off, when the outlet water temperature gets too hot.  The attached graph shows that it has been cold enough outside for the heat pump to cycle only a couple of times during the last 24 hours.

I am not expecting FRVs on the upstairs radiators to have much effect, because we leave all the doors open.  I think convention will trump the FRVs.  One option would be to close all the doors and then balance the temperatures, before opening the doors again.  Our installer set the downstairs FRVs to match the radiator capacities, which seems like a good place to start. 

Posted by: @grahamf

↑

I followed your advice and the room temperature drifted up slightly to around 20.5C, even hitting 20.7C at one point.  I am not sure that this was due to the thermostat temperature increase to 30C, as the very gentle upward trend had been continuing for several days - since we had our roof put back on!  

Anyway, I adjusted the weather compensation Shift down from +2 to +1, the smallest adjustment possible.  The temperature is now tracking 20C closely, without any intervention from the thermostat.  The heat pump turns off, when the outlet water temperature gets too hot.  The attached graph shows that it has been cold enough outside for the heat pump to cycle only a couple of times during the last 24 hours.

Good, what Id expect, you may need to tweak the WC as the temperature cools down, but hopefully thats it

Posted by: @grahamf

↑

I am not expecting FRVs on the upstairs radiators to have much effect, because we leave all the doors open.  I think convention will trump the FRVs.  One option would be to close all the doors and then balance the temperatures, before opening the doors again.  

As you obviously realise there is nothing the heating system can do to counter heat rising into open bedrooms if you want to maintain them at a lower temperature.  You could balance the rooms with the doors closed, but if you always leave them open, whats the point, you are creating artificial conditions for the balancing which dont represent how you are going to operate.  If the convection up the stairwell is too much your only options are

1.  To have separate cooling upstairs (or open windows)

2.  To keep the doors shut 

3.  Somehow to pipe warm air from upstairs back downstairs (MVHR can sometimes be used to do this)

Alternatively you could forcibly keep the upstairs at the same temperature as downstairs (by turning up the rads), but that might be uncomfortable. 

Thats just life, more specifically physics, which sometimes doesn't work in the way we would ideally like it to!

@jamespa (Thinks) I wonder if this is a reason for people living in ‘upside down’ houses? The sleeping areas are downstairs and living spaces upstairs. Toodles.