Plumbing ASHP / Unitower / UFH etc

[BartW]

Hi,

I am currently doing the plumbing for my heating system. 

 

I am following the attached diagram. Except for the fact that we have no rads, but only three separate UFH manifolds (one per floor).

 

What I am unclear about is:

- do I need a bypass valve? Some sources say it is optional. And if I do, do I get an auto bypass valve? @Nickfromwales suggest gate valve in this post: 

 

- we are using a valiant 45L buffer tank. Current plan to 4 tappings. LHS top for primary HP flow / LHS botom for primary HP return / RHS top for secondary flow to UFH / RHS bottom for secondary return from UFH. Some sources suggest (and Vaillant buffer manual as an option) to run only primary flow through the buffer to secondary flow, whilst having the return piped right through. Any benefits to one over the other?

 

Our heating arrangement is most likely:

- GF manifold: single zone (possibly keeping the guest room as a separate zone)

- FF manifold: single zone (or all three bedrooms separated, but maybe not...)

- SF manifold: single zone 

 

Many thanks!

 

Bart

 

[JohnMo]

44 minutes ago, BartW said:

Some sources suggest (and Vaillant buffer manual as an option) to run only primary flow through the buffer to secondary flow, whilst having the return piped right through. Any benefits to one over the other?

On a smaller buffer, you get plenty of mixing between the flow and return which requires the heat pump to put slightly hotter water to compensate, so there is a cop hit with the four port plumbing. You also need an extra pump on the secondary side. You do not need a bypass with this arrangement as the buffer acts as one.

The two port plumbing of buffer, mixing doesn't matter as there is no interaction between flow and return, so you may get better CoP.  A bypass valve may be required, depending on how you arrange your zones. You don't need a secondary circulation pump as the circuit is now all primary. The buffer becomes a volumiser.

 

Generally you are going to a lot of pumps running all the time if you are not careful with the design.  At the moment you have ashp circ pump, secondary circuit pump, one pump per UFH manifold. On a 6 month heating season, that could be £200 running costs just for the circulation pumps.

 

 

[BartW]

21 minutes ago, JohnMo said:

On a smaller buffer, you get plenty of mixing between the flow and return which requires the heat pump to put slightly hotter water to compensate, so there is a cop hit with the four port plumbing. You also need an extra pump on the secondary side. You do not need a bypass with this arrangement as the buffer acts as one.

The two port plumbing of buffer, mixing doesn't matter as there is no interaction between flow and return, so you may get better CoP.  A bypass valve may be required, depending on how you arrange your zones. You don't need a secondary circulation pump as the circuit is now all primary. The buffer becomes a volumiser.

 

Generally you are going to a lot of pumps running all the time if you are not careful with the design.  At the moment you have ashp circ pump, secondary circuit pump, one pump per UFH manifold. On a 6 month heating season, that could be £200 running costs just for the circulation pumps.

 

 

Thanks!

 

yes many pumps and cost of running those. Upper floors are likely to work / run very little, but it could add up. 
 

the secondary pump is part of the kit, ao am in two minds whether to install anyway. Top floor pump sits at 6m above GF FFL. That could put a lot of strain on the Unitower pump?

 

in two minds about buffer piping…

 

 

[JohnMo]

Have you installed the top level UFH piping?

[BartW]

14 minutes ago, JohnMo said:

Have you installed the top level UFH piping?

Yes all in. 

[Dreadnaught]

Are you aware that you can contact Vaillant directly and they will provide a custom system design for your particular setup. That's what I have done.

 

They ask for the name of your Vaillant adviser and I just used the name of the local area rep without having ever spoke to him. They did not seem to mind.

 

(In my case, I have my heat pump and UniTower on site. I have done the physical installation of the heat pump only so far. I have not installed the UniTower yet. Nor have I made the hydraulic and electrical connections for the heat pump, although I have bought the parts for the hydraulic connection.)

 

 

[Nickfromwales]

2-port buffer all day long, and then you can lose a pump.

[PeterW]

11 hours ago, BartW said:

 

I am following the attached diagram. Except for the fact that we have no rads, but only three separate UFH manifolds (one per floor).

that diagram is incorrect and I think has been superseded but the mag filter should be on the final cold return to the ASHP and not the far side of the buffer or it will not catch the crap how it should do. 

 

8 hours ago, Dreadnaught said:

Are you aware that you can contact Vaillant directly and they will provide a custom system design for your particular setup. That's what I have done.

Sadly they use pretty standard drawings these days and don’t actually fully check their flows (or didn’t on one I saw, also check above) and had a 3 way valve plumbed wrongly… worth following all the pipes on the plan in all scenarios ..!

[BartW]

Ok, thanks lads, so in a nutshell:

 

- run the buffer LHS top flow in - through to - RHS bottom flow out? Then cold return pipe to pie.

- Can loose the pump, or should? I feel it would help push water around the house, no? I am not worried about the cost of running it. More to ensure the rest of the individual pumps do not sweat too much.

- install a bypass valve? Automatic or manual?

-magna clean to go cold return fairly close to the Unitower?

 

 

 

[JohnMo]

 

21 minutes ago, BartW said:

feel it would help push water around the house, no? I am not worried about the cost of running it.

The pump in the heat pump will do that, when you plumb the buffer as a 2 port.

 

Having two pumps in the primary circuit you actually start getting into hydraulic issues, as the pump in the heat pump wants to modulate to manage Diff Temp, the other pump makes the control of the two pumps very erratic. If you have pumps on the UFH manifolds these will pull water through the mixing valve, the hydraulic sepereration is then across the mixing valve.

 

The biggest difference between a 4 port buffer and 2 port is the hydraulic sepereration. A 4 port gives you a primary circuit - ASHP to buffer and secondary - buffer to rest of heating system. You need a pump in each circuit. Piping as a 2 port does not give hydraulic sepereration the buffer just becomes heating volume.  The ASHP to heating system is all primary circuit.

 

I just have my whole UFH system either on or off, no actuators on the manifold. A single thermostat which, either has the ASHP on or off. All run off the circulation pump in the heat pump, also have no buffer.

[dpmiller]

Depending on demand, pipe lengths and sizing, you might even *need* a second pump on the primary to get the required flows. We have two, and the ASHP's internal one has no issues slowing down enough to allow full modulation.

[BartW]

My only concern was top floor manifold, but it is not a very big installation otherwise. From the boiler room to the top floor manifold there is merely 12m of length in 22mm. Yet after yesterday's sunny day I conclude I might, indeed (as previously suggested on BH) never run it once in the gym. I will probably have to look into air con at some point...

 

 

[Jenki]

This feels like a good place to add to rather than a new topic.

 

My pre plumbed tank with buffer is 4 port. My UFH loops have approx 30l water, then Around 8m flow and return 28mm pipe. So the buffer is required, plus it gives me an immersion for solar divert. If available / required.

I'm thinking of re-piping and blanking two of the ports off and putting the buffer in the return leg to ASHP

 

So my thinking is  bottom of three way connected to UFH manifold. Blank this port off.

The return from the manifold into the buffer (RH top port- red label).

Blank off bottom RH port. Leave ASHP return as is.

 

Any issues with this?

 

However I like the idea of having an additional pump to circulate water in the UFH circuits to even the slab temp out with any solar gain etc. But this wouldn't be possible if I did the above🙈. Decisions, decisions

 

P.s. the buffer is just 4 bosses, no additional dip tubes, baffles, pipes etc inside.

[JohnMo]

5 hours ago, Jenki said:

However I like the idea of having an additional pump to circulate water in the UFH circuits to even the slab temp out with any solar gain etc

I have tried this a few times - it made no difference to our house, so really wouldn't bother. In fact I was so unimpressed, I took the facility off the heating system. Keep as simple as possible.

 

Don't see why you buffer/volumiser config wouldn't work.