What size of air source heat pump to install? Would really appreciate any help

[sharpener]

55 minutes ago, Beelbeebub said:

Have they launched it already? 

 

My comment was based on this:

 

On 28/06/2023 at 12:53, sharpener said:

Went to the Installer Show at the NEC yesterday, lots of interesting stuff.

 

Many more HP companies have got their newly-developed R290 models now on test and will be bringing them to market late '23 to early '24.

 

Among these I talked to were Grant (will be made by Chofu)...

Edited January 15 by sharpener

[Andy T]

On 15/01/2024 at 12:28, sharpener said:

With a plain simple underfloor heating system they should be able to install the Grant 10kW to run efficiently. I  see it is not the new one with R290 refrigerant which would be a be a shade more efficient, perhaps that is not yet available in the 10kW size.

 

Was a bit puzzled you had to add double glazing to a house built in 2000, I wonder what other corners were cut?

 

What was the result of yr second heat loss calc and what are the flow temps needed in yr UFH to meet the expected worst case losses? What is the outside temp you are designing for? The 7kW Arotherm Plus is a reputable R290 unit and as  @JohnMo says, might well be adequate also unless you are on Dunstable Downs or in a similar exposed position.

 

I have recently been on a Homely training seminar and I am not convinced it would be advantageous for a simple setup like yours. It sounds as though you would quickly get to grips with the fine tuning without it.

I take your point re the window replacement. The house was built in 2000 and generally seems good, but the windows installed were softwood (perhaps a lack of money towards the end of the build?), were not maintained in any way and therefore rotted, hence total replacement required.

 

I have the heat loss report here in front of me but I'm honestly not sure how to answer the question re the flow tempts needed in the UFH - I'll try and make sense of this. We are in fact pretty exposed in a semi-rural area - we are at the top of a small hill with fields all around us. The house takes a pretty good battering on windy days! Yes, I wondered if the Homely would be unnecessary for us - we are not looking for something particularly finely tuned after happily surviving on the oil fueled underfloor heating.

[Andy T]

On 15/01/2024 at 17:49, JohnMo said:

The Grant unit can be installed in two ways a buffer/low loss header configuration, buffer gives hydraulic separation between heat and UFH - you do not want this configuration.

 

The other is a system volumiser - a buffer is installed in the supply piping only. This is ok.

 

Ideally you want, UFH as a single zone, no buffer, no mixer and no additional pumps, just run on weather compensation.

 

Heat pumps have a minimum system volume as long as your system configuration complies no need for a buffer.

 

But installers want to install in buffers

I can see on the quote it states "we have allowed for all associated pipework for the connection and fitting of the Grant external unit and cylinder valves, pumps and volumizer/buffer tank".  It is to supply and fit a Grant Aerona 3 Air source heat components:

1 No. 10kw R32 Inverter Driven HPID10R32 unit

1 No. installations pack A (HPIDR32PACKA)

1 No. UK Elite High performance 250L cylinder

1 No. Grant Mag 1 filter

 

 

[Andy T]

On 15/01/2024 at 17:30, sharpener said:

 

 

Get them to draw a diagram of the system they propose and explain what all the components are for. Not so you can find out for yourself, but so you can tell if they know themselves.

Thank you. Good idea. I will ask for a diagram

[JohnMo]

1 minute ago, Andy T said:

volumizer/buffer tank

I would ask them to clarify which volumiser/buffer they intend to install.  Grant do several including externally mounted, vertical and ones within the cylinder.

[Andy T]

2 minutes ago, JohnMo said:

I would ask them to clarify which volumiser/buffer they intend to install.  Grant do several including externally mounted, vertical and ones within the cylinder.

Okay. Thanks JohnMo. 

[sharpener]

37 minutes ago, JohnMo said:

I would ask them to clarify which volumiser/buffer they intend to install.  Grant do several including externally mounted, vertical and ones within the cylinder.

 

Pack A includes a small one for installation indoors. Looks reasonably appropriate to me though you might get away without one at all.

[JohnMo]

1 hour ago, sharpener said:

 

Pack A includes a small one for installation indoors. Looks reasonably appropriate to me though you might get away without one at all.

Unfortunately it's instructions give two ways to install, low loss header with hydraulic seperation or volumiser without hydraulic seperation. It really best to install without hydraulic seperation, to have lowest possible flow temperature. So clarity required.

 

So layout should look like this

 

[Andy T]

This is incredibly helpful and again I'm really am grateful. I had a quite chat with the installer today (as they are ordering the equipment) and have agreed to speak again to discuss installation. I'm going to print all of this out and study it over the weekend to hopefully give me a full understanding of what I'm trying to achieve and agree with him.

 

Again, I'm so grateful for the time everyone for the time and advice that's been given here. 

[sharpener]

Entirely agree with @JohnMo's last posting. If they propose anything more complicated than that diagram you need the rationale to be explained.

 

I note it does not show anti-frost drain valves (IMO work of the devil anyway) so you need to ensure they add glycol for frost protection, especially since you are on a hill!

 

[JohnMo]

11 minutes ago, sharpener said:

anti-frost drain valves (IMO work of the devil anyway)

Must agree, great until you get a power cut and they actually activate, then you have no heating until you repressurise the system. OK if your handy, but not so good if you are not, or you are away. Glycol system just picks where it left off prior to power cut.

[sharpener]

Have never understood why they ever became popular. They compromise the lagging and also introduce more joints, and in our case would create an ice rink in the pedestrian entrance way. The price of the glycol is about the same as a pair of a/f valves anyhow.

 

But as you say, worst of all is you could come back to a home which is not only stone cold but cannot be heated easily or quickly.

[PhilT]

On 17/01/2024 at 15:40, JohnMo said:

It really best to install without hydraulic seperation, to have lowest possible flow temperature.

I'm wondering if this (see photo) gets you the best of both worlds. The LLH (vertical black cylinder - capacity c. 2 litres) is connected such that only the primary flow (right top/bottom) can loop back around into the primary circuit. The LLH secondary return (bottom left is sealed off, instead rejoining the primary circuit return from the LLH further back downstream to the heat pump, thus eliminating any mixing of secondary return with primary feed.

[JohnMo]

Think if you want zones or you don't have enough system capacity the Gant volumiser or the attached Kensa scheme are better. Hydraulic seperation just add inefficiency, as it's too easy to have a heat imbalance

[HughF]

There are Two things that should always be designed out - hydraulic separation, and glycol…. Both the work of the devil.

[sharpener]

23 minutes ago, HughF said:

There are Two things that should always be designed out - hydraulic separation, and glycol…. Both the work of the devil.

 

Agree wholeheartedly about hydraulic separation, it is a sticking plaster for poor system design.

 

I don't like glycol either but IMO it is the least worst option for protecting a big capital asset against catastrophic damage without requiring (a) mains power or (b) a seldom-used cheap mechanical device to work first time when you need it.

 

(Yes I am also thinking of service valves under the sink, and pump isolating valves, usually the spindle seals fail when you operate them in anger, giving you two problems where you had just one to begin with. Had this happen on me over Christmas. Not everyone will keep a spare pump c/w valves in the garage.)

[Beelbeebub]

Is glycol so bad? 

 

Here's a table (chofu) of the correction factors for glycol 

 

Even at 40%, which gives protection below -20C the loss of capacity is only 2.6% and the pressure drop only 3.3% more. 

 

I'd argue that a system designed so that those margins are critical is maybe top close to the edge. 

 

 

I do see the reluctance to using glycol in a system with a huge (say 100l) buffer or volumiser but we should be aiming to remove those anyway

[SteamyTea]

51 minutes ago, Beelbeebub said:

Even at 40%, which gives protection below -20C the loss of capacity is only 2.6% and the pressure drop only 3.3% more. 

The heat capacity may change, but I am not sure that makes much difference.

High heat capacity fluids are used because they require less power to move them about, but as the pumping power is so low anyway, I don't think you would measure the difference in a heating system.

[sharpener]

2 hours ago, Beelbeebub said:

I'd argue that a system designed so that those margins are critical is maybe top close to the edge.

 

+1

 

Useful table thanks. There are in fact two temps involved for a given concentration (a) the lowest temp for free circulation of the working fluid (in table above AIUI) and (b) a lower burst temp where the fluid is a mush which won't pump easily but the system is still protected against frost damage. Another table here comparing the two, for both ethylene and propylene glycols.

 

For any given temp you can save about 1/3 glycol if you don't need the system to actually work(!)

[Iceverge]

Maybe I'm late to the battle here but have you considered if an ASHP is a good idea?

 

They work well at low flow temps and prolonged operation periods and good building fabric. 

 

UFH and solid uninsulated floors shouts high flow temperatures and intermittent heating to me.  To get the desired output from a heat pump you will have it run it at higher flow temps (bad for COP) for long periods. This means very high electricity bills. 

 

Maybe I'm missing something?

 

[JohnMo]

4 hours ago, Beelbeebub said:

Is glycol so bad? 

 

Here's a table (chofu) of the correction factors for glycol 

 

Even at 40%, which gives protection below -20C the loss of capacity is only 2.6% and the pressure drop only 3.3% more. 

 

I'd argue that a system designed so that those margins are critical is maybe top close to the edge. 

 

 

I do see the reluctance to using glycol in a system with a huge (say 100l) buffer or volumiser but we should be aiming to remove those anyway

We can get -9 here, but I made the decision to add about 10 to 15% anti freeze to the system. Accept I maybe getting an efficiency hit. 

 

Mitigation were, need all to coincide together,

1. you need a power cut to coincide with the coldest day,

2. I need to away at the same time, to ensure 4 is implemented 

3. we have a battery it needs to be flat, but we always keep 5% in reserve

4. and we have a generator that needs to be connected - it may not start.

5. Also cool down time to the water getting to freeze point will be reasonably long. So you need a long power outage.

[Beelbeebub]

1 hour ago, sharpener said:

 

+1

 

Useful table thanks. There are in fact two temps involved for a given concentration (a) the lowest temp for free circulation of the working fluid (in table above AIUI) and (b) a lower burst temp where the fluid is a mush which won't pump easily but the system is still protected against frost damage. Another table here comparing the two, for both ethylene and propylene glycols.

 

For any given temp you can save about 1/3 glycol if you don't need the system to actually work(!)

But we're only interested in freeze protection if there is no power. 

 

If there is power then the fluid temp won't ever be below zero so the increced viscosity at very low temps isn't an issue. 

[Beelbeebub]

6 minutes ago, JohnMo said:

We can get -9 here, but I made the decision to add about 10 to 15% anti freeze to the system. Accept I maybe getting an efficiency hit. 

 

Mitigation were, need all to coincide together,

1. you need a power cut to coincide with the coldest day,

2. I need to away at the same time, to ensure 4 is implemented 

3. we have a battery it needs to be flat, but we always keep 5% in reserve

4. and we have a generator that needs to be connected - it may not start.

5. Also cool down time to the water getting to freeze point will be reasonably long. So you need a long power outage.

Glycol/Antifreeze valves are very much for the chance combination of rate events (though power cuts are often correlated with very cold weather). 

 

I understand the reluctance for glycol especially if you have a huge system volume, but I do think the case against it has been overstated - especially regarding efficency. 

 

For me the biggest "downer" is the potential mess from leaks, either during use or spillages during maintance, but then again spilling water from a cruddy open vented system is pretty nasty anyway. 

[sharpener]

2 hours ago, Iceverge said:

UFH and solid uninsulated floors shouts high flow temperatures and intermittent heating to me.  

 

OP wrote

 

On 04/12/2023 at 11:06, Andy T said:

We have a detached chalet style bungalow, with solid (concrete) floors and with an underfloor wet heating system, currently run on Kerosene oil. The property was built in 2000

 

but I would be very surprised if a house built in 2000 has no insulation under the concrete floor. We haven't any record of what was used in a 1995 barn conversion, but the HP installers agreed that min 50mm insulation was likely and have used that in their calcs. Somewhere there is a table showing what the Building Regs required at various dates in the past.

[sharpener]

1 hour ago, Beelbeebub said:

But we're only interested in freeze protection if there is no power.

 

Not quite. The scenario might be we return from a winter break in the Canaries and find the house in darkness from a lengthy power cut. It has been a sunny day so there is enough charge in the battery system to run the HP for >2 hrs  though. Frost protection would mean we can heat the house, burst protection not. Fortunately we have a WBS, an oil-fired AGA and even oil lamps.