Can you explain the DT comment a bit more.  If the temp is coming in at say 28 degrees to the rads and leaving at 28, then the energy transfer must be zero.

Yes thats true, but that cant happen unless the room temperature is 28C!

Its best in most circumstances to think of DT as a consequence of other things, not something you control.  The emissions from a radiator are determined by its average surface temperature in relation to the room temperature.  The first of these is principally determined by the flow temperature.  So a radiator of a given area with an average surface temperature of 28C and a room temperature of 20C will emit a certain amount of heat.  This, together with the flow rate will determine the DT.  There is a bit of circularity here because a higher DT means a lower average surface temperature for any given flow temperature, so to do the calculation you have to iterate a few times (nature of course does the iteration for you).  Thats why a lower DT (which, if all else stays the same, can be achieved by increasing the flow rate) will actually result in a higher emission from the radiator in any given set of circumstances.

To complicate matters further some heat pumps have a DT control loop.  This secondary control loop modulates the water pump to target a specific system level DT.  However the DT variations as described above will still occur at the level of the individual emitters, so balancing for room temperature is still effective.

The rads are sized a bit small for the flow temp the UFH needs, so I need a little more temp.  I've closed 2-3 of the UFH heating loops as suggested but its not cold enough really to see it its helped. 

Yes.  So you can:

• reduce the DT across the rads by increasing the flow rate through them.  This increases their average surface temperature for any given FT.  The effect is limited though - if you start with a DT of 5 then the best you can get (at flow rate = infinity) is a DT of 0, 2.5C higher average temp
• increase the DT across the UFH by reducing the flow rate through it.  This reduces the average surface temperature for any given FT.  The effect is essentially unlimited, with zero flow rate (ie closing loops), the average surface temp falls to the room/slab temp so there are no heat is emitted
• increase the radiator area
• reduce the UFH area (which you are doing by closing loops)

One thing to be careful with if you close loops completely is that it reduces the system volume - ie the volume of water in the active sysem.  This will reduce the 'on' period when the heat pump is cycling, which reduces efficiency.  Its probably better to turn them all down very low than switch some off completely, but of course that depends on practicality.  In extremis if you reduce the system volume too far you can get into a problem with defrost, where there isn't enough hot water in the system to melt the ice that forms on the compressor.  This can cause a death spiral.  Heat pump manufacturers specify a minimum system volume for this purpose (in reality you want a larger system volume so that cycling is more efficient).

Hi, thanks for getting back to me. 

this week will be more interesting as its getting colder here is Sheffield.

Can you explain the DT comment a bit more.  If the temp is coming in at say 28 degrees to the rads and leaving at 28, then the energy transfer must be zero. So if the DT is 1, then is it not that only a bit of heat is transferred to the room at any given flow rate.  The rads are sized a bit small for the flow temp the UFH needs, so I need a little more temp.  I've closed 2-3 of the UFH heating loops as suggested but its not cold enough really to see it its helped. 

I'll keep you updated 

@toodles 

sorry, my bad. Its a 6 port LLH.  of the 2 higher ones, the rad circuit is the lower of those 2. 

I wonder what the logic of this was, that will be the cooler of the two whereas I would have thought you want the rad circuit on the warmer.

Never mind it shouldn't matter that much, how is the balancing going, are you getting closer?  From what I recall your problem is that its too cool upstairs where you have radiators, and too warm downstairs, where you have UFH.  More flow through the radiators and less flow through the UFH should sort this unless the radiators are too far undersized in the first place; has adjusting the relative flows made any difference? 

Say my flow/return is 30/25, the DT of the rads is only 1, and the UFH slightly over 5.  I’ve spoken to my installer about getting more DT off the rads.

Dont!  The adjustment you need to make will reduce the DT through the rads and will increase the DT through the UFH.  Thats the mechanism by which the UFH emits less (because the average temperature is reduced) and the rads emit more (because their average temperature is increased), which is what you are trying to achieve.  DT is much misunderstood!

Just to be clear the way the balancing works is this: 

The loss from an emitter (to the room) is determined by the average temperature of the emitter. 

If you increase the flow through an emitter then the average emitter temperature will increase because the DT across the emitter decreases as a result of the increased flow.  This will increase the loss from the emitter to the room (which will cause the DT to increase a bit, so if you are calculating it you need to iterate, but the real world does this for you). 

Conversely

If you decrease the flow through an emitter then the average emitter temperature will decrease because the DT across the emitter increases as a result of the reduced flow.  This will decrease the loss from the emitter to the room.

Thus, given what you have told us, Im expecting your system to be in balance (for temperature) when the DT across the radiators is relatively low and the DT across the UFH relatively high.

sorry, my bad. Its a 6 port LLH.  of the 2 higher ones, the rad circuit is the lower of those 2. 

Normal practice is that the top port opposite the flow from the heat pump would feed the heating circuit. The lower ports are for the return from the end of the heating pipework into the LLH and the port on the opposite side feeds back to the heat pump (return). This means that the flow from the heat pump enters one side at the top of the LLH and the flow out to the radiators is on the opposite side, also at the top; the return enters the LLH on the same side as the port that flows to the radiators but at the bottom, and the fourth port at the bottom is the return to the heat pump. This is the normal route to reduce distortion (mixing) to the minimum; at this point it is advantageous to minimise any difference in temperature across the ports by controlling the pump’s flow rate to further reduce didtortion.  Regards, Toodles.

Hi, thanks for reply. 

I've started to play, its still very warm outside so need it to get cooler, but I've closed 2 loops out of 9 where we are most overpowered with the UFH, This did increase the flow temp to the rads by a degree (I was getting a small amount of blending at the LLH, the rads is the lower out from the header so got blended by a degree). the rads are now seeing the primary flow temp. So I assume i've just nudged the secondary flow (hard to measure) to slightly below the primary flow (31 l/min) 

@davidnolan22 Hi, ok first of all it very hard to truly balance duel UFH circuits and rads when they have a shunt, Splan valve and a manifold pumps, usually we would want an open loop system to have one pump controlled by the ASHP supplying the whole balanced system. 

Isn't this a great example of KISS!

Brands Like Ecodan and many others have duel zone control and can modulate the flow slightly to different circuits but you would need to run the system hotter and unfortunately blend back down at the UFH manifolds to control the flow temperature which then can also cause a higher return on the flow and short cycle the ASHP. 

You may find that if the UFH loops are over designed for a flow rate of 40℃ and the rads are under designed for a flow rate of 30℃, so if you choose 30 the rads are short and if you choose 40 the UFH is over.  

Some tricks that may work. 

If you have multiple loops on the UFH example: lets say you have 4 loops in the dining area spread out like loops 123and 4 in order left to right you could close down loops 2 and 4 or 1 and 3, this would half the power of the UFH but keep it kind of spread out, if it is slightly over designed, this would then let you run the system at 40/35 and add more power to the rads.

Just make a note by taking pictures or videos of where settings are before adjusting anything so you can always put it back where it was.

Any heating system has little chance of working correctly if it is not balanced.

I know its confusing, I am half guessing how your system is set up and assembled so I may be making some assumptions, also balancing the systems needs quite a few measurements.

If you can get an actuator and UFH stat in the hall way and close down 1 loop in the hallway this would control half the output in the hall and control this area if it over heats.

If there are 2 loops in the UFH hallway you may be able to close one down to reduce the output. they system then could have the curve raised and allow more power to the rads and less would be in the UFH circuit in this one area.

I am hopefully giving you options here if the system is out of design.