GSHP, Buffer tank and UFH

[Fraser Lamont]

Anyone have any advice on circulation pumps - after moving from non buffered with half my loops open to a completely zoned and buffered situation? My external heating circulation pump (nearest Ground Source Heat Pump) is wired to what looks like a small consumer unit on the wall. I think the GSHP controls this when on 'summer disconnect', I believe it's the only time of year that it gets switched off. I was told by the supplying company that the pump would always be on outside of the summer months to keep water in the loops because the Heat Pump needs to sense water return temps. Now I have a buffer tank, all zoned areas are controlled by thermostats, the manifold controllers (one each for ground and first floor) turn off their respective circulating pumps when no heat is required, but the pump external to the Ground Source Heat Pump keeps going. Now that I have a Buffer Tank, should this pump now be wired and controlled directly by the Heat Pump? I'm concerned because if no heat has been called for from either manifold - all loops will be closed and the circulating pump will be continually pushing water against closed circuits. Diagram attached - I haven't included the pipe runs for the Domestic Hot Water. Many Thanks

[Nickfromwales]

Hi. 
When the heating is satisfied and no stats are calling for heat, does the pump you’ve indicated between the buffer and the manifolds shut off?

[Fraser Lamont]

19 minutes ago, Nickfromwales said:

Hi. 
When the heating is satisfied and no stats are calling for heat, does the pump you’ve indicated between the buffer and the manifolds shut off?

Hi,

no, it was designed for half my heating circuit to be open permanently but the house was 28c. It was designed that way so the Heat Pump could always sense what the return temp is, thereby work out when to cycle the heating. That was before every room had it's own Temp controller - the Heat Pump was doing that job before (crudely). Now I have full zones and buffer, I think the Heat Pump should now be only switching that circulating pump when it's on underfloor heating mode - for just now I've had to remove the Valve Motorized Head (manifold) from one of my upstairs bathrooms just to stop the pressure from the pump fighting against closed circuits. The other 2 pumps on manifolds only come on when a room calls for heat (Heatmiser UH1-W). My Installation book does mention controlling the "External main pump in the heating system G1(P1): The external main pump should be connected to the terminal card in those cases a bypass is required. The pump is connected to terminal P1". I do have a bypass installed - nowadays they probably use automatic bypasses. Thanks

[Fraser Lamont]

52 minutes ago, Nickfromwales said:

Hi. 
When the heating is satisfied and no stats are calling for heat, does the pump you’ve indicated between the buffer and the manifolds shut off?

The other thing, if the main circulation pump is rewired to the heat pump then switches off when not in heating mode, there'd be no return water for the heat pump to work out the temperature of the water in the system. There's always a 5c difference, say the water return is 34c (cold outside temperature), then the heat pump cycles until the return water temperature hits 39c then stops. Would I then have to rely on the main indoor air temperature sensor which provides settings such as how much influence (1 - 10) the heat pump should use based on these readings? Jeez, this could get complicating

[SteamyTea]

@joe90

Can't you just turn off the heating control so it never calls for heat?

 

I got a new mate that is learning all about ASHPs and stuff. He would fiddle with it till it was bust.

Edited April 12, 2021 by SteamyTea

[joe90]

16 minutes ago, SteamyTea said:

Can't you just turn off the heating control so it never calls for heat?

Yes I do, currently back on for this cold snap but usually in the summer it’s off.

[joe90]

On 10/05/2019 at 13:52, BotusBuild said:

That's not strictly a buffer tank

I disagree. @Nickfromwales ? Your thoughts please. ?

[Nickfromwales]

[Nickfromwales]

1 hour ago, joe90 said:

I disagree. @Nickfromwales ? Your thoughts please. ?

 

On 10/05/2019 at 13:52, BotusBuild said:

That's not strictly a buffer tank - that's a hot water tank. A buffer tank has no coil inside it.

Buffer tanks do have coils, so they can promote true hydraulic separation whilst still maintaining heat transfer between mediums.

Buffer tanks commonly have no coil, agreed, but the above is inaccurate.

2 hours ago, Fraser Lamont said:

no, it was designed for half my heating circuit to be open permanently

Then it's a shit design.

The call for heat signal should be made to the GSHP from a tank / cylinder stat on the buffer tank. The GSHP will ramp down and switch off when that stat is satisfied, in heating mode aka winter, and then the energy in the buffer tank gets depleted and calls for heat again. The buffer should have been sized according to the system size and heat demand eg to stave off short cycling.

The buffer tank should only be between the GSHP and the buffer, and the DHW UVC should see the GSHP directly. That means the buffer only heats in the winter  

This needs to be rewired by someone who knows what they're doing. It's not a million miles out, just needs tweaking to set it up properly.

The pump you show should be brought on by the 230v supply that brings the manifold pumps on, but that needs to be via a pair of relays so the two manifold pumps cannot 'see' each other eg one manifold with demand cannot then inadvertently back feed the second manifold pump. At this stage ideally you want a 2-port zone valve on each manifold, after the buffer > UFH pump, and before each manifold. Then each 2-port zone valve will provide this separation and they then control the pump instead. That's how it should be have been set up in the first place imo. See diagram

 

[Nickfromwales]

Zone valve A and B would be on the flow to manifold 1 and 2 respectively.

[Nickfromwales]

[Nickfromwales]

2 hours ago, Fraser Lamont said:

Jeez, this could get complicating

 

[Fraser Lamont]

@Nickfromwales would this work, a bypass at the end of one of the manifolds? My system is getting on for 15 years old now, the first couple of years the upstairs bedrooms and bathrooms only were on thermostats, I had to retrofit the controllers for downstairs, far too hot, very cheap to run because of all the water pipes in concrete, but too warm.

Edited April 12, 2021 by Fraser Lamont

[Fraser Lamont]

 @Nickfromwales could a bypass between flow and return on one of the manifolds work, as above?

 

Edited April 12, 2021 by Fraser Lamont

[dpmiller]

Are there no thermo mixers on the manifolds?

[Fraser Lamont]

No, temperature to underfloor manifolds varies between 28c and 40c max throughout the year

 

Edited April 12, 2021 by Fraser Lamont

[dpmiller]

is that the flow or return temp?

[Fraser Lamont]

Return Temp. Today for example, when the return water goes down to 34c, the ground Source Heat Pump starts the heating cycle and keeps going until the return hits 39c. The water temperature being sent out from the GSHP is approximately mid 40c to increase the temperature within all the underfloor heating loops. I'm on the Isle of Skye, Highlands, and it was so cold last night that my car door was frozen shut. Water temp leaving the heat pump to UFH never goes above mid to high 40's and every room is 21-22c. A decent enough size house with 4 x bathrooms, hit with all sorts of weather (coastal), I love the system - only problem is retrofitting upgrades not always easy, it was designed purely for economics (running costs) by the company I bought it from. Care should be taken to include comfort but this system is nearly 15 years old now, installed it when I built my house

[Nickfromwales]

On 12/04/2021 at 16:32, Fraser Lamont said:

 @Nickfromwales could a bypass between flow and return on one of the manifolds work, as above?

 

You cannot daisy-chain through the 2 manifolds as shown. The arrangement needs to be plumbed as per my scribbling. The bypass only needs to be installed if there is a situation where the buffer pump is on when the UFH manifolds are both satisfied and all zones have shut ( eg if you have an incorrectly installed / plumbed / wired system which you appear to have. The proposal for use of yur system from get-go is crude on a good day and is not a design |I would offer or promote, let alone install and walk away from.

Stop asking about quick fixes, there aren't any  

[Fraser Lamont]

On 14/04/2021 at 14:47, Nickfromwales said:

You cannot daisy-chain through the 2 manifolds as shown. The arrangement needs to be plumbed as per my scribbling. The bypass only needs to be installed if there is a situation where the buffer pump is on when the UFH manifolds are both satisfied and all zones have shut ( eg if you have an incorrectly installed / plumbed / wired system which you appear to have. The proposal for use of yur system from get-go is crude on a good day and is not a design |I would offer or promote, let alone install and walk away from.

Stop asking about quick fixes, there aren't any  

 @Nickfromwales It's my last drawing which is a bit crude, the system was designed for me almost 15 years ago for my self build house (Ice Energy). I wasn't accurate regarding the manifolds which look daisy chained but they're not. A fairer representation of my heating circuit is like this 

[Nickfromwales]

Ah, that makes much more sense, cheers for that.

You should still have 2-port zone valves at each manifold though, as it’s those which should be bringing on the buffer > manifold pump according to demand ( as per my diagram / wiring / valve arrangement ). 
It really boils down to how often the heating is on with both manifolds routinely having at least one open loop each, simultaneously, for the duration of each heating on’ period. That will decide if you should relax or start cutting.