Heat pumps. Any negative points about 3 phase?

[saveasteading]

We've been assuming 2 x heat pumps because there will be two distinct zones. It's too big for one unit on single phase.

But it is  all one family building and we have 3 phase power available, already into the premises. 

 

I'm aware of the principles of 3 phase efficiency on motors, so presumably this will be preferable.

Maybe also not require additional internal distribution pumps.

 

But are there any downsides?

 

The only one I foresee is family arguments over dividing the bill. Any technical issues?

 

[-rick-]

Doesn't really matter too much on modern heatpumps as they are all inverter driven. ie, they convert the incoming power to DC and then generate custom 3 phase (both voltage and frequency) to drive the motor. A traditional heat pump that didn't have the inverter would gain a little efficiency (and reliability from less components) from 3 phase supply but irrelevant today.

 

Generally, 3 phase heat pumps don't start until about 15kw. Is your heat loss really that high? Anything you can do to lower it?

[SimonD]

19 minutes ago, -rick- said:

Generally, 3 phase heat pumps don't start until about 15kw. Is your heat loss really that high? Anything you can do to lower it?

 

The Panasonic M series Aquarea is available in a 9kW 3ph unit. It is very nice indeed and super quite, even if it is physically quite large.

[saveasteading]

34 minutes ago, -rick- said:

Anything you can do to lower it?

Teach people to shut doors, and not wash dishes under a hot tap.

[-rick-]

9 minutes ago, saveasteading said:

Teach people to shut doors, and not wash dishes under a hot tap.

 

I was thinking more along the lines of add more insulation, reduce air leakage, etc. Assumed this question was in relation to the building you are in the process of converting from a cow shed. In which case there should be lots you can do to improve things if your loss is that high. (Though I'm not sure how you'd be meeting building regs on a new construction with a high heat loss). If it's an older building, then likely lots of easy things you can do to bring the loss down.

 

And as usual on this forum, it's worth checking where you have got the heat loss calcs from? The heatpump installers have a terrible record of vastly overestimating it which can then lead to wrongly sized systems and poor operation. Though as a regular I assume you know all this already?

Edited yesterday at 12:41 by -rick-

[SimonD]

1 minute ago, -rick- said:

And as usual on this forum, it's worth checking where you have got the heat loss calcs from? The heatpump have a terrible record of vastly overestimating it which can then lead to wrongly sized systems and poor operation. Though as a regular I assume you know all this already?

 

Good point. Given his background, experience and attention to detail, I just assumed @saveasteading would have it all covered off.

[saveasteading]

10 minutes ago, -rick- said:

lots you can do to improve

Don't worry on that score. It's effectively a new building. The floor insulation was delivered yesterday. 4 lorry loads for 300mm th.

No , my over-whimsical comment is that behaviour change is all we could do. Or add MVHR which we have decided not to after due consideration of cost/benefit.

 

I'd have to move chairs to check but I think we were looking at 7 +5 kW and now 1 x 11kW. There seem to be lots.

[JohnMo]

You building must be massive to need that size heat pump, as effectively a new build?

 

5-600m²?

[saveasteading]

16 minutes ago, JohnMo said:

5-600m²

yup. There will be a fair bit of heat wasted to the  high vaulted spaces, and some biggish glazing. but otherwise it's normal.

If the heat pump/s end up turning  off more than expected then we can live with that.

We are fortunate in having a known, proven big-time plumber who is advising foc first, then we are prob working cost plus. and I think we will buy the materials... again a favour and based on trust...

Not that they will be cheap, but it is far too big for a smaller outfit anyway.

 

The reason I am asking you, dear BH posters, is the overview, beyond the simple sums.

 

eg noise and airflow.

how lumpy a cable to get through the house.

and the unknown unknowns.

 

 

[SteamyTea]

2 hours ago, saveasteading said:

 

I'd have to move chairs to check but I think we were looking at 7 +5 kW and now 1 x 11kW. There seem to be lots

Why not one HP and some supplementary resistance heating for the coldest times?

 

[Nickfromwales]

2 hours ago, saveasteading said:

Teach people to shut doors, and not wash dishes under a hot tap.

#victoriandad

 

lol. 

[Nickfromwales]

1 hour ago, saveasteading said:

There will be a fair bit of heat wasted to the  high vaulted spaces, and some biggish glazing. but otherwise it's normal.

 

2 hours ago, saveasteading said:

Or add MVHR which we have decided not to after due consideration of cost/benefit.

 

[Wil]

I’ve got 2 3ph ASHPs. Cables not particularly chunky as they’re running at less than 20A as the power is split across the phases. That was my main driver to keep the loads spread on my connection and avoid a huge peak consumption on a single phase which would exceed my 60A fuses.

 

Yes they’re big. They’re 15m away from the house behind an outbuilding so noise isn’t an issue. Pipe runs were annoying but are what they are. 300m2 and seem to run at about 5kW heat loss at 3degrees outside temp. House is a bit of a frankensteins monster of new bit, well insulated and old bit not so much.

[saveasteading]

2 hours ago, Nickfromwales said:

 

We reckoned it was 20 years' payback for mvhr . We will spend half as much on a biggish photovoltaic array and battery and get a much better return.

and putting both in would reduce  the heat recovery benefit.  ie if we are getting free power and then multiplying the energy by , say , 4 then using powered fan to recover free heat...

That is logical, yes?

 

We may also install big visible, attractive  fans (Spanish style) in the vaulted areas to send down the hot air that has risen.

 

The easiest way to increase the apparent efficiency would be to put rooms instead of vaulted space. Same energy nut divided by a larger floor area. But it is style and flashness.

 

 

[Nickfromwales]

13 minutes ago, saveasteading said:

We reckoned it was 20 years' payback for mvhr . We will spend half as much on a biggish photovoltaic array and battery and get a much better return.

and putting both in would reduce  the heat recovery benefit.  ie if we are getting free power and then multiplying the energy by , say , 4 then using powered fan to recover free heat...

That is logical, yes?

Who cares about payback? MVHR is for quality of air. Consider the HR element to be a bonus as then you're not pulling freezing cold air in all winter and paying "powered fans" to spin to recirculate stagnant heat from the vaulted areas.

 

Genuinely quite shocked to hear this approach thb, but 'different strokes' I guess....  I'm buggered if I would ever spend all my life savings and then be pulling cold air in and puking heated air out to the clouds for the rest of my life!!

[saveasteading]

10 minutes ago, Nickfromwales said:

shocked to hear this approach thb,

It simply hasn't ever been a problem in any of our projects. About 5 family ones and many commercially.

I think the reason may be that we only ever designed for the minimum airtightness requirement, so allowing some fresh air in. 

Plus window vents and openable windows always.

If there is no problem with air quality then there is nothing to fix.

 

On a few of our projects I feared a problem with stuffiness (school classrooms, nursing homes) but we discussed the options with the client and went for it.  These were clients who would have had a quiet word with us if there was  problem, but there hasn't ever been a word.

 

This reminds me of the SE practice we employed for many years. They didn't do the portal frames part for us, but founds, other elements and other structure types

Our main contact SE had either had, or knew about, many, expensive, problems with steel buildings and couldn't see how ours didn't ever have any problems.  We concluded that we must have been lucky 300 times.

 

Maybe, by building to the current reg's on airtightness but without mvhr, , we will have a stuffy building for the first time. If vents and windows won't do the trick, then we have a plan B which will be local extractor fans, discretely placed, perhaps linked to CO or CO2 or humidity sensors. Of course the fans' air will be replaced by un-heated air  from the tiny leaks, and heated by our cheap electricity.

It is a risk, but we are experimenting on ourselves.... But I'm confident it will be fine....  and lucky again.

 

Edited 1 hour ago by saveasteading

[Nickfromwales]

4 minutes ago, saveasteading said:

Plus window vents and openable windows always

All winter?

[saveasteading]

18 minutes ago, Nickfromwales said:

All winter?

As necessary, if at all.

The Steading isn't stuffy in he slightest.  not as airtight as a newbuild would have to be, but plenty good enough.