Grant ASHP DIY install

[crispy_wafer]

So, I managed to bag a small Grant ASHP which I intend self installing, as much as I possibly can.

 

It'll be a relatively simple system comprising DHW and UFH, Spark and plumber will be doing the wiring and cylinder for me.

 

So getting stumped at the first hurdle, as I start looking for other bits needed for install... 

Although I'm a bit hesitant to ask questions as it shows my lack of knowledge somewhat, here goes the first few questions to enter my head..

 

How would I size the pipework from the ASHP to the UFH manifold, is there a rule of thumb?

The UFH has a design flow rate of 16.4 l/min, and the manifold is a max of 10 metres away from the heat pump.  5 bends at the most as the pipe goes up round and down! 

 

How do you decide if a buffer is needed? 

UFH Design volume is about 96 Litres this is a ground floor system, and all the loops are in rooms which will be used frequently so I'm happy to have the system act as a single zone.

 

Pumps?

Should I rely on the ASHP pump solely, or wire up the UFH pump too, then would I need to have a LLH, or is this a case of check the pump on the UFH circuit and see if it closely matches with the pump settings on the ASHP?

 

Cheers

Marek

 

[ProDave]

UFH manifolds with a circulating pump and a temperature blending valve should be used.

 

I used 22mm pipe but the plumbers may have a better recommendation.

 

the Grant install manual will specifify the minimum system volume, they sell their own "volumiser" that can be used as s a simple extra volume or piped as a low loss header, again I will leave that to the plumbers.

[DanDee]

25 minutes ago, ProDave said:

temperature blending valve should be used.

 

 

 

Question - what is there to blend?

[sharpener]

How small is a "small" unit?

 

Stick with the min pipe size to match the HP tappings as per the Grant instructions here, which is 3/4 in or 22mm for the smallest.

 

There are also the Chofu instructions here which do show UFH but unlike the diagram on p14 you could omit the blending valve. As @DanDeeimplies this is only required for a boiler flow at ~60C, then you do not need a secondary pump or LLH either. As you will see from the curves on p13 even the 6kW unit has a pump easily able to push 16 l/s against a sizeable pd, actually it can develop a higher pressure than the 10kW.

 

Grant do stipulate using a volumiser, you will still need this to prevent short cycling on DHW only.  On p13 they say install it on the flow if it has an auxiliary heater, however on p18 they show it on the return which has lower losses, there are extensive discussions about this on this forum.

 

Good luck, let us know how you get on!

[JohnMo]

To give you an idea of the process I used to design my system.

 

My 6kW heat pump is located 10m from the house.

 

Have run 28mm from HP to house (10m each way), then dropped to 22mm inside house (500mm), short run to a 22mm 3 way valve, then 500mm to UFH manifold.  Not using mixing valve and pump on UFH (many will not like that).  From the 3-way valve to cylinder is a further 10m and is already existing in plastic 22mm, so my pressure drop is at the end of that allowable for the ASHP circulation pump, so have installed a second pump on the return leg to run only in DHW heating mode.  This will be run at a constant volume flow.

 

I downloaded pressure drop charts for the different pipes, bends and calculated the system pressure drops to make sure I was ok on the curve for the flow required.

 

You need a buffer if the smallest possible open circuit volume is below the minimum volume specified within the manual.  The more you are over this volume the better.  I will have over 60l circuit size, so will not use a buffer.  My Manifold will have no actuators on it so will always be open.

 

2 hours ago, crispy_wafer said:

Should I rely on the ASHP pump solel

I would if you can, keep it simple

 

2 hours ago, crispy_wafer said:

would I need to have a LLH,

Try not to keep it simple.

 

Generally keep it as simple as possible, if you only have UFH and no radiators just run on weather compensation.

[sharpener]

23 minutes ago, JohnMo said:

You need a buffer if the smallest possible open circuit volume is below the minimum volume specified within the manual.  The more you are over this volume the better.  I will have over 60l circuit size, so will not use a buffer.  My Manifold will have no actuators on it so will always be open.

 

 

Useful stuff @JohnMo but what is the volume of the DHW circuit and how do you stop it short cycling on DHW only? I imagine this is why the Grant manual requires a volumiser under all circumstances. Though AFAICS the Chofu manual does not. (Also it may not be current as I have just noticed it says R410a refrigerant.)

[JohnMo]

1 minute ago, sharpener said:

volume of the DHW circuit and how do you stop it short cycling on DHW only?

That is why you have a large coil in your cylinder, the cylinder becomes the engaged volume.  You don't need a volumiser or buffer on the DHW side of the system.  It is normal to have a buffer on the central heating side of the 3 way valve.

 

I think I have added the CO2 manual for you.

Chofu-Operating-Installation-Manual.pdf

[JamesPa]

9 minutes ago, sharpener said:

Useful stuff @JohnMo but what is the volume of the DHW circuit and how do you stop it short cycling on DHW only? I imagine this is why the Grant manual requires a volumiser under all circumstances. Though AFAICS the Chofu manual does not. (Also it may not be current as I have just noticed it says R410a refrigerant.)

I pondered this question until one prospective installer, who was otherwise hopeless, pointed out that there are two reasons for a large coil in the dhw tank.  The first, and most often quoted, is reheat time.  The second is to avoid short cycling.  I then did some modelling of heat loss to dhw vs coil size as a function of temp diff between flow and dhw tank.  Conclusion was that a 5 C temp diff and a 3sq m coil was ok with my planned hp which modulates down to 4kW

[crispy_wafer]

1 hour ago, sharpener said:

How small is a "small" unit?

 

Stick with the min pipe size to match the HP tappings as per the Grant instructions here, which is 3/4 in or 22mm for the smallest.

 

There are also the Chofu instructions here which do show UFH but unlike the diagram on p14 you could omit the blending valve. As @DanDeeimplies this is only required for a boiler flow at ~60C, then you do not need a secondary pump or LLH either. As you will see from the curves on p13 even the 6kW unit has a pump easily able to push 16 l/s against a sizeable pd, actually it can develop a higher pressure than the 10kW.

 

Grant do stipulate using a volumiser, you will still need this to prevent short cycling on DHW only.  On p13 they say install it on the flow if it has an auxiliary heater, however on p18 they show it on the return which has lower losses, there are extensive discussions about this on this forum.

 

Good luck, let us know how you get on!

 

Ta, it's their 6kW unit.

I've downloaded the installer guides from Chofu and Grant had a skim read earlier at work, primarily trying to identify the sections for the weather compensation settings.

 

I'm popping out tomorrow to go fetch it.  Measured up and it will fit in the back of the Shogun standing up so happy with that.  I'll spend the next couple of weeks laying my hands on bits and bobs to do the install.  I'll keep updating the thread as I go, hopefully it will serve as a half decent reference point for others in the future,

[sharpener]

Sorry @JohnMo but it is the same R410a one, the current Grants use R32 though it is not clear what exactly the OP has bought, perhaps he will tell us?

 

<It is normal to have a buffer on the central heating side of the 3 way valve.>

 

Not what the Grant manual shows, [6] is the volumiser in the pic below. If you are going to have one at all then I would think it would still help to have it in circuit for the DHW (as they do). But you could argue that when the CH cuts in you have the extra volume of water at a higher temperature than you want/need/is good for the efficiency.

 

N.b. the pic shows an S-plan setup, this allows both circuits to be in use at once, best not to allow this as the temps you want are very different esp without a blending valve. As others have said this allows for a drop-in boiler replacement in a system with just rads, but the downside is you get far from optimal efficiency with any attached UFH.

 

 

@JamesPa <wrote Conclusion was that a 5 C temp diff and a 3sq m coil was ok with my planned hp which modulates down to 4kW>

 

So almost certainly OK with the OP's 6kW unit then.

 

Edited March 14, 2023 by sharpener

[crispy_wafer]

It's an R32 unit!

[sharpener]

So up to date then. The difference might explain the better CoP figures mentioned by @DanDee in this thread.

[JohnMo]

16 minutes ago, sharpener said:

Grant manual shows, [6] is the volumiser in the pic below. If you are going to have one at all then I would think it would still help to have it in circuit for the DHW (as they do).

It on the return leg which good

[Bonner]

I have a Grant 13kW MCS installed. Can’t vouch for it’s performance yet but  the installers seemed to know what they were doing. Two UFH manifolds, radiators and a separate towel rad circuit.  Grant supplied package including volumiser. PM me if you want any more info.

 

[crispy_wafer]

10 minutes ago, Bonner said:

I have a Grant 13kW MCS installed. Can’t vouch for it’s performance yet but  the installers seemed to know what they were doing. Two UFH manifolds, radiators and a separate towel rad circuit.  Grant supplied package including volumiser. PM me if you want any more info.

 

 

Pictures are great, gives me something to work towards, when I pickup the tools up in anger!  Your guys have used press fit too, which is cool!  I'm looking to snag a tool on ebay at the moment, I think they are amazing bits of kit.  

[ProDave]

Here's one I did earlier.  Well I only did the wiring, not the plumbing.

 

UVC and volumiser supplied as a package with the ASHP.

 

I am not sure I agree with the plumbing, but there are two UFH manifolds a second one just to the right out of shot and the only circulating pump in the system is the one in the ASHP.  And no thermal mixing valves on the manifods so water circulates at temperature set by the ASHP.

 

[Jenki]

6 hours ago, JohnMo said:

  Not using mixing valve and pump on UFH (many will not like that). 

So just a basic manifold with isolation valves? Simple.

[sharpener]

13 hours ago, crispy_wafer said:

Pictures are great, gives me something to work towards, when I pickup the tools up in anger!  Your guys have used press fit too, which is cool!  I'm looking to snag a tool on ebay at the moment, I think they are amazing bits of kit.  

 

I notice all the gleaming new copper pipe in these two pix, albeit with push-fit fittings. What do ppl think about using PolyPlumb, I have used it a lot for my rainwater harvesting system and found it so much easier to work with.

[JoeBano]

Isn’t the bore smaller on plastic? 

[DanDee]

12 minutes ago, JoeBano said:

Isn’t the bore smaller on plastic? 

 

https://heatpumps.co.uk/pressure+flow/simulator.html

[JoeBano]

13 minutes ago, DanDee said:

 

https://heatpumps.co.uk/pressure+flow/simulator.html

That’s a good link didn’t realise 10mm plastic is the same as microbore. 

[sharpener]

45 minutes ago, JoeBano said:

Isn’t the bore smaller on plastic? 

 

Thanks both, will have to factor that in. Flow rates seem to be almost exactly 1/2 with 10mm and 2/3 with the rest. Hope I might save as much on bends as lose on straights though.

 

Had refit of ch in another house ~8 yrs ago, plumbers used all plastic (except for rad tails for appearance), must have cost them (?me) a fortune in fittings and labour as they still had a copper-pipe mentality and put in heaps of elbows instead of just bending the plastic.

Edited March 15, 2023 by sharpener

[ReedRichards]

If you buy a modern "low temperature" gas boiler, my understanding is that it is set up for a 20^oC drop between flow and return.  If you buy a heat pump it is generally set up for a 5^oC drop between flow and return.  For the same rate of heat input this would mean that the heat pump has to have a flow rate four times as fast as the gas boiler.  I don't understand why there has to be such a disparity; perhaps it's just different traditions?  But heat pumps use high flow rates so need larger bore pipes.       

[JohnMo]

I have played with boiler settings quite a bit over the last year or so and found the following.

 

70 and above, the boiler control will modulate flow rate to achieve a delta of 20.

 

But - as you bring the flow temperature down, the delta T also comes down also, when you have a flow temp in the high 20s to low 30s, the delta T is around 5 or 6, the pump flow rate is automatically adjusted to maintain this.

 

So is working very similar to a heat pump.

[crispy_wafer]

Popped over to Liverpool yesterday to pick up the little beastie.  Got it from a renewables firm that had installed a few of these, but the heating calcs system they were provided with had some under sizing errors.  They then had to pull these units out at of use and replace, so were selling the small units off.  Had about 2 weeks worth of work, comes with controllers and most of the bundled accessories.

 

1st job on the agenda is sorting out it final position, then putting in the condensate drain and concrete pad.  I'm redoing the soil and waste drainage outside as I don't like the builder did.  So, any reason I cant feed the condensate into a 110mm which will eventually end up in the WTP?