Plant Room Distance from ASHP - 25m too far?

[SBMS]

Currently planning on ASHP positioning relative to plant room.  Plant room is on top floor (room in roof) and, by my calculation, it's going to be a 25m run from the outdoor unit, to the cylinder, controller and plumbing etc.  All of this 25m is inside the house/thermal envelope (just an annoying, complex route, and it's got to get from ground level to 6m to attic floor)...  Is this going to be a problem?

[Dillsue]

Shouldn't be a problem with the right sized pipes. 

 

Remember that your not pumping up to the loft but circulating up there and back down again. The flow up to the loft will be working against gravity but the return back down to ground floor will be working with gravity and the two gravitational "resistances" cancel each other out.

 

All your circulation pump needs to overcome is the restistance of the pipe work and fittings

[SBMS]

1 hour ago, Dillsue said:

Shouldn't be a problem with the right sized pipes. 

 

Remember that your not pumping up to the loft but circulating up there and back down again. The flow up to the loft will be working against gravity but the return back down to ground floor will be working with gravity and the two gravitational "resistances" cancel each other out.

 

All your circulation pump needs to overcome is the restistance of the pipe work and fittings

Does this pump typically exist in the heat pump (outside) or in the loft?

[Beau]

Our Vallient has the circulation pump in the heat pump 

[Nickfromwales]

Some do and some don’t so you may want to just look for one either way an external pump if worried, but upsizing the pipework to maybe 35mm should remove the issue of the additional hydraulic resistance, (meaning you can have the pump wherever, but more importantly you won’t have to be worried that you’re then wedded to that particular OEM pump (and its performance not being inadequate))

[JohnMo]

Our run to cylinder is circa 25m. Some of the pipe around 7 to 10m is in 22mm plastic pipe, the rest is 28mm (6kW ASHP). Heat pump circulation pump didn't have enough power to get from A to B and back with sufficient flow rate. So use a second pump just for cylinder heating via a close coupled tee.

[SBMS]

Thanks all 👍

[Originaltwist]

I've seen an ASHP parked in the woods well away from the house,  to avoid noise and unsightliness, and that worked OK. I expect a secondary pump was needed.

[sharpener]

4 hours ago, Beau said:

Our Vallient has the circulation pump in the heat pump 

 

Avoid secondary pumps if you can. The Vaillant internal pumps are exceptionally powerful so with the correct pipe sizing I don't think you would have any problem. This is for the 12kW size, nominal flow rate is about 2100 l/hr so you have 55kPa (8 psi or 5.6 m head) to play with:

 

 

Edited March 16 by sharpener

[Bramco]

4 hours ago, Nickfromwales said:

but upsizing the pipework to maybe 35mm

But that leaves a LOT of hot/warm water in a pipe before it gets to the house.

On a previous house, we installed microbore from the solar thermal to the tank to make sure that we didn't have a pipe full of hot/warm water but nothing in the tank on dullish days where things turned on and off.

So maybe a smaller bore pipe for the 25m run and a secondary pump to help it on it's way.  Wonder if anyone has done any real world tests on this?

[JohnMo]

8 minutes ago, Bramco said:

Wonder if anyone has done any real world tests on this?

 

3 hours ago, JohnMo said:

Our run to cylinder is circa 25m. Some of the pipe around 7 to 10m is in 22mm plastic pipe, the rest is 28mm (6kW ASHP). Heat pump circulation pump didn't have enough power to get from A to B and back with sufficient flow rate. So use a second pump just for cylinder heating via a close coupled tee.

Do a test nearly everyday 

[Bramco]

So parallel pipes one 22mm and one set 35mm?

 

There's a big difference in the volume of water...   and would be interesting to see what effect both (or more) bores have on the effectiveness of the ashp, especially when defrosting - there could be a large volume of warmth heading out of the house to the ashp when it's already done it's thing and defrosted...

[SBMS]

Stupid question (I know little of plumbing) but if a secondary pump were needed can it live at the end of the 25m run, in the plant room? Or does it need to be next to the ASHP?

[SBMS]

39 minutes ago, sharpener said:

 

Avoid secondary pumps if you can. The Vaillant internal pumps are exceptionally powerful so with the correct pipe sizing I don't think you would have any problem. This is for the 12kW size, nominal flow rate is about 2100 l/hr so you have 55kPa (8 psi or 5.6 m head) to play with:

 

 

We are looking at the vaillant aerotherm 12kw so that sounds useful re the pump - is its internal pump powerful enough to push 25m?

[Nickfromwales]

1 hour ago, Bramco said:

But that leaves a LOT of hot/warm water in a pipe before it gets to the house.

👇   👍

7 hours ago, SBMS said:

All of this 25m is inside the house/thermal envelope

😎

[JohnMo]

3 hours ago, Bramco said:

So parallel pipes one 22mm and one set 35mm?

Who is going to do that? 

 

12kW pump has huge flow needs, so 22mm would be sh*te anyway.

 

Sounds like a pressure drop calculation is needed to me. But second pump would ideally be hydraulically separated.

[SBMS]

7 minutes ago, JohnMo said:

Who is going to do that? 

 

12kW pump has huge flow needs, so 22mm would be sh*te anyway.

 

Sounds like a pressure drop calculation is needed to me. But second pump would ideally be hydraulically separated.

Did you do a pressure drop calculation for your 25m run? Or was it less risky with a smaller ASHP?

[Nickfromwales]

3 hours ago, SBMS said:

Stupid question (I know little of plumbing) but if a secondary pump were needed can it live at the end of the 25m run, in the plant room? Or does it need to be next to the ASHP?

I'd get a pump matched to the OEM and speak to technical to see if they can share the same PWM feed cable. If not, then you'll need a dumb-ish pump that is somehow hydraulically separated from the OEM unit, prob achievable by a small low loss header.

 

LINK

[JohnMo]

4 minutes ago, SBMS said:

Did you do a pressure drop calculation for your 25m run? Or was it less risky with a smaller ASHP?

Yes. More risky the smaller the circulation pump. I use a small Wilo pump in addition to ASHP circulation pump. The primary circuit (ASHP circulation pump) does around 1.3m³/h and get around 1.0m³/h from the Wilo on the secondary circuit. Seems to work fine.

 

A 12kW heat pump will be doing twice those flow rates.

[sharpener]

1 hour ago, JohnMo said:

Sounds like a pressure drop calculation is needed to me. But second pump would ideally be hydraulically separated.

 

How difficult can this be?

 

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

 

So for a 12kW Vaillant the flow rate is 34 l/min, which over a 50m total pipe run has a pressure drop of 90 mbar with 35mm Cu pipe, and 250 mbar with 28mm which is 3.6 psi. 

 

Available head as upthread is 8 psi which allows as much again for indoor pipework and fittings so unless these are very restrictive I think you would be OK with 28mm. Volume in pipe 27 litres which is no big deal.

 

If necessary you can just add a secondary pump in series with the flow, controlled from the MA terminal on the Vaillant interface unit, and adjust the 2o settings so the two pumps share the head loss.

 

But most installers would probably play safe and fit a low loss header, close coupled tees or a buffer tank. These are all a bad idea as there will then be what Heat Geek call "distortion" i.e. mixing resulting in an increase of entropy, which will unavoidably reduce the CoP.

[Gus Potter]

11 hours ago, Dillsue said:

Shouldn't be a problem with the right sized pipes.

 

7 hours ago, Originaltwist said:

I've seen an ASHP parked in the woods well away from the house,

For me I think of district heating.. common thing to do in plenty parts of the world.

 

Main thing for me is keep it simple and stupid. You might need an extra automatic air vent here and there, other than that it should be fairly straight forward.

11 hours ago, Dillsue said:

Shouldn't be a problem with the right sized pipes. 

 

Remember that your not pumping up to the loft but circulating up there and back down again. The flow up to the loft will be working against gravity but the return back down to ground floor will be working with gravity and the two gravitational "resistances" cancel each other out.

 

All your circulation pump needs to overcome is the restistance of the pipe work and fittings

Agree. But this works up to a point. Simplistically when the main circulating pump (sending the water to and from the house) is off the static water head is equal in the flow and return. For reference 1 bar =  atmospheric pressure = 30 feet (~10 m) of a static water column. A good domestic Grundfos pump can pump a 6.0m head and if it gets a good start it might just create a negative below atmospheric pressure in the return pipe before it gets going and settles down. You kind of want to avoid this as it causes cavitation in the pump and that can shorten it's life span.

 

Therefore any automatic air vents should be located on the feed (pressure side) if the upper floors are say 4 - 5 m above the ASHP. That's my qualitative assumption which assumes you don't have too many bends etc in the pipes.reality the best thing to do is give it your best shot and have a strategy.. if it does not work then have leave access to add in extra bits!

 

[MikeSharp01]

I am going to start a campaign to sort the basic insult that has become embodied in KISS (Keep It Simple, Stupid) - the comma is important. It was envisaged as not being an insult when Kelly Johnson a lead designer at Lockheed Martin in the 1960s first coined it, more of a note to self and to stress simplicity. Sadly it is often not used like that these days so I tend to use it now with a slight rearrangement to KISS (Keep It Stupidly Simple)  which, for me, makes it less insulting when people use it talking to others. Rant over.....

[JohnMo]

10 hours ago, sharpener said:

But most installers would probably play safe and fit a low loss header, close coupled tees or a buffer tank.

I think this where you need to do some research (not @sharpener) but the OP.

 

ASHP run different algorithms - mine for example runs a very simple one, the circulation pump runs full speed when doing DHW and only at full speed. So I don't actually need a hydraulic separation between primary and secondary pumps. You only need when you havextwo pumps that can run variable speed as they fight each other.

 

A second pump could quite easily be added (on the DHW side of the diverter) to start up when the diverter valve moves to DHW (from same power source) and switch off when the diverter moves to central heating.

 

You then just change speed to get circulation rate you want.

 

If you have variable speed pump operating during DHW, you need hydraulic separation IF you run the second pump with variable speed, or if you run second pump as above only on fixed speed then you don't need hydraulic separation. The main circulation pump will not then have a fighting match.

[sharpener]

6 hours ago, JohnMo said:

ASHP run different algorithms - mine for example runs a very simple one, the circulation pump runs full speed when doing DHW and only at full speed.

 

Vaillant are even simpler. When on Auto and supplying heat either to DHW or CH the internal pump runs at max flow rate, for a 12kW that is 34 l/min, smaller sizes pro rata. You can change it to a specific residual head if you want but mostly they run fine on Auto. 

 

Modulation is achieved by varying dT not flow rate. The pump runs at a lower speed only when the Energy Integral s/w is not calling for heat so the HP is idling.

[JohnMo]

If that simple just add a pump on either the flow side of the diverter to DHW or the return side prior to teeing into the return from the CH. Run at a fixed speed that enough head to get the circulation rate you need. Do the piping in 28mm. Simple enough.