Right, I think I've finally got my head around the whole setup for ASHP's. It has taken me a while to adjust to the method of thinking as multi zoning etc seems to be the common method generally accepted by Building Control

I propose the following:

1. Run the heatpump 24hrs a day - This is because it will run a more efficient COP due to the lower temperatures required to maintain a stable temperature as opposed to higher temps. for shorter time periods

2. Run UFH (kitchen and bathroom) on one zone and rads on a separate zone (the rest of house). UFH will be 15mm Hep20 Barrier pipe, maximum loop 100m, set 100mm apart. Rads will be fed with 22mm Hep20 pipe with 15mm run to each rad. Or do I just run the rads and UFH off a single zone and let the TRV's do the controlling??

3. Run the whole house at the same time with no zoning per se - Reason being that if you just heat one room the heat will escape due to high delta T so best to heat whole house even if unoccupied

3. Do not use weather compensation function, simply adjust the temperatures manually starting from 30c and working up to 45c flow (my design temp.) during the colder weeks. This is what John Cantor advised in a private email exchange. This was based on the fact the weather compensation means it runs a lower COP during the night time due to the colder evenings. He believes that ASHP should adopt average temps rather than weather compensation.

5. Run all radiators on TRV's for controllability and personal comfort. Will also aid in any rooms that have higher solar gain etc getting too hot. As I intend to run a woodburner in the living room a TRV will be useful as it will shut off the rad as the heat builds up from the stove

6. Run the UFH using an in floor temperature sensor (can you recommend one or do I need two??) to keep the screed temperature at 1c above required air temperature. These sensors essentially operate a TRV on each UFH circuit. Kitchen screed will be 75mm, bathroom screed will be 25mm biscuit mix

7. Based on 6, would I therefore need some form of blending valve or not required for the UFH?

8. Is there a requirement for a central thermostat or just switch on/off at the controls and leave on for the heating season? Maybe set it to an outside temp. so when delta T between outside/inside hits a required level say 5c or more?

I think this is keeping it very simple and hope I haven't missed anything as I will be running the pipework over the next week?

can anyone offer advice please?

Hi Victorianeco

Some thoughts below:


1. Run the heatpump 24hrs a day - This is because it will run a more efficient COP due to the lower temperatures required to maintain a stable temperature as opposed to higher temps. for shorter time periods.

Makes sense

2. Run UFH (kitchen and bathroom) on one zone and rads on a separate zone (the rest of house). UFH will be 15mm Hep20 Barrier pipe, maximum loop 100m, set 100mm apart. Rads will be fed with 22mm Hep20 pipe with 15mm run to each rad. Or do I just run the rads and UFH off a single zone and let the TRV's do the controlling??

If you have 2 zones you will need to 230v stats (from memory its an Ecodan you are using). If you haven't got a buffer and I would suggest you use one, we would fit 28mm for the main circs. 100m loops unless in a snail are too long, 80m max for flow rates and high delta T.

3. Run the whole house at the same time with no zoning per se - Reason being that if you just heat one room the heat will escape due to high delta T so best to heat whole house even if unoccupied

Makes sense but see the note above about rads and UFH on separate zones, the TRV's are effectively creating zones, they just don't interlock with the heat pump but they will create the same issue you are wanting to avoid.

3. Do not use weather compensation function, simply adjust the temperatures manually starting from 30c and working up to 45c flow (my design temp.) during the colder weeks. This is what John Cantor advised in a private email exchange. This was based on the fact the weather compensation means it runs a lower COP during the night time due to the colder evenings. He believes that ASHP should adopt average temps rather than weather compensation.

I have worked with John on a project and admire him and his work, but a legion of northern europeans cant be wrong on weather compensation. Clock your hot water production off over night and poss setback your air temps, with a more sophisticated heat pump you can set back the flow temps over night but not on the Ecodan. We have found though that setbacks tend to end up costing you more unless the house is very well insulated.

5. Run all radiators on TRV's for controllability and personal comfort. Will also aid in any rooms that have higher solar gain etc getting too hot. As I intend to run a woodburner in the living room a TRV will be useful as it will shut off the rad as the heat builds up from the stove.

Fine but with the caveats above and if you have no buffer we wouldn't recommend using TRV's at all to increase water volumes and to provide for defrost energy.

6. Run the UFH using an in floor temperature sensor (can you recommend one or do I need two??) to keep the screed temperature at 1c above required air temperature. These sensors essentially operate a TRV on each UFH circuit. Kitchen screed will be 75mm, bathroom screed will be 25mm biscuit mix

The Ecodan has to have a 230v connection to a stat to start so bear this in mind when selecting controls. This is one of the reasons we are reluctant to fit them, most northern europeans will respond to a sensor and a resistance value.

7. Based on 6, would I therefore need some form of blending valve or not required for the UFH?

Depends on your design flow temps, for rads/ufh but MCS query whether there is one in case you are running high temps and blending down.

8. Is there a requirement for a central thermostat or just switch on/off at the controls and leave on for the heating season? Maybe set it to an outside temp. so when delta T between outside/inside hits a required level say 5c or more?

As before the Ecodan is not the best unit in terms of control, because it needs a 230v signal, resistance based is much more accurate. If you have 2 zones you will need 2 stats and 2x2 ports valves. Whichever is calling will switch the unit on from the actuator switch on the zone valve.

If you want to keep it simple, 1 stat and open zones,high flow rates, but your design has to be bang on.

Hi Victorianeco, we will take on sub-contract MCS jobs but only to experienced trade and it has to be local to us which is north Derbyshire.

In terms of the rads I am unconvinced that the tolerance on a TRV is that fine anyway,its a wax capsule, often sitting vertically above a pipe influenced by the heat rising from it (they should be horizontal) and next to a heat source (the radiator) and that's if they aren't in sunlight or behind a curtain!

Basically the design has to be bang on, but it is tricky because this includes full knowledge of the heat loss based on insulation values, system design,balancing etc.

In practice we have done plenty with minimal or no control without issue. If you can split upstairs and downstairs that can be a reasonable compromise.

Hi V,

It's very difficult to get 100mm between joists and the amount of notching and restrictions on notching of the joists under building regs usually means you don't get the coverage to achieve floor outputs. An option where you can increase the floor height is to cross batten with roofing laths and notch these instead.

We would always advise you go for a small <5kw wood burner because you don't need any additional ventilation which screws your heat loss.

Heat pumps, UFH and wood burners are not ideal partners to be honest, especially with a screed/slab, which can take hours to change in temperature enough to offset the output from a WB.

You have a choice to make in terms of control too, on 1 hand you could use a floor probe that will keep the floor on while the wood burner is in, or an air stat to switch off the supply to the floor as the air temp rises.

In practice our clients with a combination of UFH, a WB and a heat pump rarely use the WB.

Or even just run everything on one zone including the kitchen UFH but use some kind of floor probe to limit flow like a TRV type control?

"UFH needs to be run at temperatures (circa 30°C) well below those used in radiators (c. 80°C). The standard way of reducing the temperature of water in mostly radiator systems uses a thermostatic mixing valve and a separate pump to circulate the UFH loop. Various cheaper schemes exist using e.g. a thermostat which blocks flow from the main CH pipework to the UFH when the UFH is up to temperature."
http://wiki.diyfaq.org.uk/index.php?title=Central_Heating_Controls_and_Zoning

And just use the bathroom UFH as 'always on'?

Let the weather compensation do it's thing