Is 5kw ASHP too small?

[ReedRichards]

1 hour ago, JohnMo said:

 

There are two ways to manage a buffer.

No thermostat.....

With thermostat 

Heat pump heats the buffer to a thermostat set point, this thermostat only managed the buffer temp, this is set hotter than heating system flow temp, works the same as a thermal store.  Heating system sucks the heat from the buffer.  Buffer is recharged by heat pump it doesn't know or care what the heating system is doing.

 

 

But your ASHP efficiency depends on how hot it has to make the water.  So having to make the buffer even hotter than the heating water must hit efficiency, surely?  

[JohnMo]

All things are a compromise, which has the bigger hit on efficiency short cycling or heating a thermostat controlled buffer?  The thermostat doesn't need setting very much above heating flow temp, hysteresis depends on volume I believe. 

 

The non thermostat buffer, doesn't require additional temperature to operate.  So win win.  That is how Kensa heat pump want the buffer installed.

 

The difference in CoP for a 5 degree uplift in supply temp for a given outdoor temp 0.5.

 

If you heat pump was sized quite closely to max heat demand, a clever option may be to bypass the buffer once it gets to about 4 or 5 degrees outside. Then short cycling should not be an issue anyway.  You just need the defrost capacity is maintained in the system.

 

[HughF]

17 hours ago, ruggers said:

What are you running in the outside lines from the compressor to indoors? Whats separating this, theres usually a wall unit isn't there with the heat exchanger in? 

I've seen the Meiflow jackets housing esbe mixing valves with control units for controlling the heating curves, and grundfos or wilo pump inside.

 

Is that set up for priority hot water with the 3 port valve? The Unistor cylinders have a 15 minute reheat time or 11 mins to 70% for a 250L 

All heat pumps are priority hot water, that's just the way they work. If you have them set to DHW+Heating (or cooling) then the DHW will be satisfied first.

 

You won't get those reheat times when driving a Unistor (or any other heatpump cylinder) with a heatpump. The reheat times in the Unistor brochure are based on the maximum flow temperature that a boiler circuit can deliver - I actually seem to remember the Unistor saying that 85 degree flow was required, at which point the coil rating becomes valid.

 

Have you played with the Freedom Heatpumps toolkit? It has cylinder reheat performance models on there based on cylinder size and coil surface area. I've attached it for your reference. 

2046225701_2021FreedomHeatPumpstoolkitV3.3forallinstallers-Copy.xlsx

[ruggers]

On 26/11/2022 at 21:07, ProDave said:

The point is, if you buy the kit and install yourself, it will probably still be cheaper without the grant, than getting the £5K grant and paying for an MCS install.

 

A monoblock ASHP comes charged with gas and does not need an FGAS installer.

I think if I was to buy Vaillant it would cost me £8750-9000 for components only no labour. I can only guess some prices. Its about 3-4k more than a gas boiler set up. The annual savings would take 15 years to recoup with the more expensive services factored in to keep a warranty unless it was all self install.
 

On 30/11/2022 at 07:05, HughF said:

Monobloc heat pumps have everything inside, you get hot water out of them. No need for an indoor heat exchanger.

 

those pipes are the flow and return and carry the central heating circuit water. 

I've tried calling Vaillant and Viessmann and Vaillant seem useless, only now and again you get someone who knows what they are talking about in renewables or technical. Basic stuff they can't answer. They don't call back. I don't think the UK knows enough about them yet, not everyone but most. Theres not enough info. available for me to feel confident in an installer or myself fitting one. Everyone Ive spoken to has a different way to do things. Your saying no need for a Hex unit, installers say outdoor unit should come to the indoor hex unit with glycol in then from the hex I can have water in my system. Or you can have a full system of glycol which sounds terrible, especially if you had a leak. Others have said no need for any glycol just water between indoor and outdoor units and some anti freeze valves.

On 30/11/2022 at 09:07, JohnMo said:

A bigger buffer gives a longer the run time and longer the off time, less cycles more efficient heat pump operation. Heating system 0.1kW to max HP output, it doesn't care.  The heating system is a separate system, you could have a 10kW heat pump driving a 2kW heating system, with a correctly sized buffer.

Some say try not to use a buffer because it loses efficiency and others say to use one. Is this just to make it easier to hide a half thought out design or they really are needed on most installs?

 

[HughF]

6 hours ago, ruggers said:

I think if I was to buy Vaillant it would cost me £8750-9000 for components only no labour. I can only guess some prices. Its about 3-4k more than a gas boiler set up. The annual savings would take 15 years to recoup with the more expensive services factored in to keep a warranty unless it was all self install.
 

I've tried calling Vaillant and Viessmann and Vaillant seem useless, only now and again you get someone who knows what they are talking about in renewables or technical. Basic stuff they can't answer. They don't call back. I don't think the UK knows enough about them yet, not everyone but most. Theres not enough info. available for me to feel confident in an installer or myself fitting one. Everyone Ive spoken to has a different way to do things. Your saying no need for a Hex unit, installers say outdoor unit should come to the indoor hex unit with glycol in then from the hex I can have water in my system. Or you can have a full system of glycol which sounds terrible, especially if you had a leak. Others have said no need for any glycol just water between indoor and outdoor units and some anti freeze valves.

Some say try not to use a buffer because it loses efficiency and others say to use one. Is this just to make it easier to hide a half thought out design or they really are needed on most installs?

 

Call a heat pump company, not a boiler company… Speak to Chris at CoolEnergy in Grimsby if you want to talk to someone technical.

 

I’ve just added a 5kW Aerotherm plus and a VRC700 to my basket on the first hit I found on Google, with delivery it’s under £4k - where are you getting the other £4k from? Give us a breakdown of your system design and we can see where you can make it simpler and cheaper.

 

Onto the glycol argument - no-one should be using glycol in 2022, a single freeze valve is all that’s required.

 

A decent monobloc doesn’t need an internal HEX unit, just get the flow and return into your plant room and hook it up directly to the system.

 

A buffer allows you to run the heat generator and the heat emitter as separate systems, with a loss of efficiency. Lots of installers use them because it eliminates callbacks for low flow errors when an existing system with too many TRVs have all the heads shutting down. A buffer also provides a large volume of water for the defrost cycle. Personally I have a small house with a simple heating system and we never have any doors closed so have no need for any TRVs downstairs. I’m going direct from ASHP into the rads, using the modulating pump in the ASHP - if I have problems then I’ll add a LLH and put a separate fixed speed pump on the rad side.

 

So yes, a buffer doesn’t make it super easy to throw a system in that will work. The ASHP sees the buffer and controls the temperature of that, the room stats/zone valves/pumps just see the buffer as a ‘boiler’.

[JohnMo]

6 hours ago, ruggers said:

Some say try not to use a buffer because it loses efficiency and others say to use one. Is

Couple of different ways to look at buffer and also what the heat manufacturer states as a minimum system requirements.

 

Some manufacturer will have a minimum system volume and minimum flow rate.  Some will specifically demand a buffer of minimum volume otherwise warranty is void.  If you have UFH with a mixer valve you have no idea of the volume flow through system will always meet the min flow requirements as the mixer recycles a lot of the flow.

 

Vaillant 8kW demands a flow between a min and max of 380 and 1400 l/h

[ruggers]

@HughF Well I plan to have have radiators and 2 towel rails upstairs ran off their own manifold in 15 or 16mm mlc, ground floor 85m2 of UFH all on weather comp.

 

My rough price guide i added up was based on what I'd picked up from brief reading only. Theres other parts I know I'd need but don't know the names or prices of them having never installed an unvented cylinder. With a gas boiler I would install 2 mixed pump sets to independently control the curves. 

 

• 7Kw ASHP £3832.20 inc vat. Heat pump warehouse. - 5Kw cheaper again.
• 250L UniStor £1208 inc vat.
• Hex module £698 inc vat.
• 25L Expansion vessel £60?
• Senso comfort - One for each floor? £200 each or 400 each? Will post link at end.
• 45L buffer tank £560 - This was Vaillant, could be other brand & could be smaller?
• Underground pipes outside £400 for 4m? Uponor do one in insulation.
• Flamco Meiflow x 2 mixed pump sets £300 each
• Electric control box to connect boiler to the mixer valves - £225 each for other boiler brands - Would need 2
• Mag filter £75
• Lagging - decent type £50
• Rotary isolator switch - Better looking black one £50
• Armoured cable from consumer unit to ASHP £25
• Glycol £?
• Pipework & press fittings for plant room £500?
• Press fit tool hire £60
• Pump & temperature sensor for buffer £100?
• Anti freezing valves £200 for 2?
• Various valves for internal plant room £150?
   
• Total £9100 inc VAT - £7300 excluding VAT (1800 VAT reclaim).
  
  Whats the difference with these?
  Why is this £835 for 2, https://www.plumbnation.co.uk/site/vaillant-sensocomfort-wired-pack-2/?fbclid=IwAR0EHaN2sOacqh48JkiexIlu2FueI1lXNCqVRxuQDlPhYNyGgt4V6BvapjY
  
  And this is VRC 720 is £195 each.
  https://www.plumbnation.co.uk/site/vaillant-sensocomfort-vrc-720-weather-compensating-room-thermostat/?fbclid=IwAR2BEGi0orMwCoxM1y-dHu1KyhTJb3XprGW_MnZFdIxlLlFkaJhl8eMkPvM
•  

[HughF]

You don’t need the mixed pump groups. The weather comp curve can be set for the radiators and then you can use a standard ufh blending manifold and pump for the ufh loops.

 

Pick a brand that doesn’t require a hex module for a start, and choose one that includes the room controller in the box. There’s really no need to go spending all that much.

[ruggers]

I can't see any difference in them two senso comforts but there must be if they're on the same site at such a price difference.

 

Them UFH manifold pump sets with the TRV style mixer are just for on off controls and don't work very well with weather comp. I could probably get away with only one mixer for the UFH and let the radiators demand the highest temperature which they usually do, but some people have rare instances where the UFH demands more than the radiator circuit. 

 

I just looked at Vaillant because they get rated highly like eco dans. Boilers I was looking at the Viessmann system boilers for their low modulation. Much cheaper than heat pumps to install. 

 

How does the water not freeze in the outside pipes? Why's the Vaillant installer saying it has to have glycol between the compressor unit and whatever it connect to indoors?

 

I'm not up to speed on the terminology of it all. 

Outdoor unit is the compressor?

Whats the monoblock?

If the hex unit is the internal heat exchanger between the indoor piping and the outdoor unit, if you don't use one, hows it all connect

[Dan F]

5 minutes ago, ruggers said:

If the hex unit is the internal heat exchanger between the indoor piping and the outdoor unit, if you don't use one, hows it all connect

Don't need HEX. Only real reason to use one is if you have glycol in your heat pump circuit, but not in your internal circuits. But even in this case it's easy just to use Glycol everywhere rather than adding costs/complexity and loosing efficiency.  That said, as @HughF says, with anti-freeze valves you don't need glycol.  I have a Vaillant install with no glycol, no HEX and a 25L buffer.

[JohnMo]

Two types of heat pump

Monobloc, everything you need to get hot water is outside, water pipes connect to outdoor unit

 

Split, smaller outside unit, but refrigeration gas pipes connect to indoor unit some of the stem is indoors, water connects to indoor unit.

 

Hex unit, just a plate exchanger and pump in flashy box.  Less efficient do to a temp drop across the heat exchanger.

 

Glycol anti freeze, stops water pipes freezing. Without a heat exchanger the whole system has to have anti freeze in it.  Split system refrigerant doesn't freeze at normal winter temp.

 

Alternative to anti freeze is freeze valves, these open when they detect water temp at or below 3 deg, dumping water to the floor.

[ruggers]

5 minutes ago, Dan F said:

Don't need HEX. Only real reason to use one is if you have glycol in your heat pump circuit, but not in your internal circuits. But even in this case it's easy just to use Glycol everywhere rather than adding costs/complexity and loosing efficiency.  That said, as @HughF says, with anti-freeze valves you don't need glycol.  I have a Vaillant install with no glycol, no HEX and a 25L buffer.

What brand is the 25L buffer?

 

I've no idea why they wanted to use glycol then, especially as a registered installer. You'd expect a random plumber to maybe do things that way.

 

I wouldn't fancy glycol throughout the whole system sounds very messy if you need to drain down or if you got a leak, plus it won't be cheap like water is.

 

Why does glycol lose efficiency. Filling the whole system including radiators would mean even less efficient?

Edited December 5, 2022 by ruggers

[JohnMo]

5 minutes ago, ruggers said:

Why does glycol lose efficiency

It has a lower heat transfer coefficient compared to water, so you have to run a degree or so warmer.

[ruggers]

8 minutes ago, JohnMo said:

Two types of heat pump

Monobloc, everything you need to get hot water is outside, water pipes connect to outdoor unit

 

Split, smaller outside unit, but refrigeration gas pipes connect to indoor unit some of the stem is indoors, water connects to indoor unit.

 

Hex unit, just a plate exchanger and pump in flashy box.  Less efficient do to a temp drop across the heat exchanger.

 

Glycol anti freeze, stops water pipes freezing. Without a heat exchanger the whole system has to have anti freeze in it.  Split system refrigerant doesn't freeze at normal winter temp.

 

Alternative to anti freeze is freeze valves, these open when they detect water temp at or below 3 deg, dumping water to the floor.

Thanks John, What have you got installed in Scotland. We have freeze issues outside up North.

If you just used the anto freeze valves, would you not just lose all of the system water every time it's below 3°C outside, is it not like a combi where below a certain pressure the system stops working until you fill it back up?

[JohnMo]

Just now, ruggers said:

Thanks John, What have you got installed in Scotland. We have freeze issues outside up North.

If you just used the anto freeze valves, would you not just lose all of the system water every time it's below 3°C outside, is it not like a combi where below a certain pressure the system stops working until you fill it back up?

I'm still on gas but been doing lots of reading, I need a cooling solution as much as anything else.

 

Heat pumps generally run a pressurised system same as combi, so if the freeze valves open the system would loose pressure.  If the system is operation ie you have power, the pump would circulate to protect the system. Only in a prolonged power cut would the water drop below 3 deg and the valve open.

[Dan F]

4 minutes ago, ruggers said:

What brand is the 25L buffer?

https://www.seconrenewables.com/volano-wall-mounted-buffer-7698-p.asp

 

4 minutes ago, ruggers said:

I've no idea why they wanted to use glycol then, especially as a registered installer. You'd expect a random plumber to maybe do things that way.

Not all installer have moved on to use anti-freeze vales.

 

[Dan F]

https://www.caleffi.com/international/en-int/catalogue/antifreeze-valve-brass-body-108601

[ruggers]

35 minutes ago, Dan F said:

https://www.seconrenewables.com/volano-wall-mounted-buffer-7698-p.asp

 

Not all installer have moved on to use anti-freeze vales.

 

Seems so. Maybe concerned where we live is too cold or just not heard of them.

35 minutes ago, JohnMo said:

I'm still on gas but been doing lots of reading, I need a cooling solution as much as anything else.

 

Heat pumps generally run a pressurised system same as combi, so if the freeze valves open the system would loose pressure.  If the system is operation ie you have power, the pump would circulate to protect the system. Only in a prolonged power cut would the water drop below 3 deg and the valve open.

I was about to say, It's nearly always 3 degrees or less in a Scottish winter so it would be leaking out constantly. So it's just if the pump has no power to it. If it's not running because theres no heat demand but it then drops down to a low temperature, it would fire the pump up instead of dumping the pressure.

[HughF]

7 hours ago, ruggers said:

Seems so. Maybe concerned where we live is too cold or just not heard of them.

I was about to say, It's nearly always 3 degrees or less in a Scottish winter so it would be leaking out constantly. So it's just if the pump has no power to it. If it's not running because theres no heat demand but it then drops down to a low temperature, it would fire the pump up instead of dumping the pressure.

Exactly…. The anti freeze valves are for the rare case where there’s no residual heat in the system, there is a power cut, and it’s freezing outside. Only then will they open and release the water to prevent freezing.

 

They are the way forward, and you only need one of them, not two as specified by most installers. And you can get them as 1/2 mount direct from china for £16. I stuffed mine into a 28mm press T

 

 

Edited December 6, 2022 by HughF

[JamesPa]

5 hours ago, HughF said:

Exactly…. The anti freeze valves are for the rare case where there’s no residual heat in the system, there is a power cut, and it’s freezing outside. Only then will they open and release the water to prevent freezing.

 

They are the way forward, and you only need one of them, not two as specified by most installers. And you can get them as 1/2 mount direct from china for £16. I stuffed mine into a 28mm press T

 

 

 

HughF you have obviously been doing good work thinking about eliminating unnecessary components - "1 valve not 2".  My current design also calls for 2 normally closed (ie closed when unpowered) solenoid valves indoors as part of the antifreeze protection, so that only the external bits, not the whole system, is drained.  Have you a design which eliminates one or either of these - they seem like a sledgehammer to crack a nut. 

[HughF]

11 minutes ago, JamesPa said:

HughF you have obviously been doing good work thinking about eliminating unnecessary components - "1 valve not 2".  My current design also calls for 2 normally closed (ie closed when unpowered) solenoid valves indoors as part of the antifreeze protection, so that only the external bits, not the whole system, is drained.  Have you a design which eliminates one or either of these - they seem like a sledgehammer to crack a nut. 

I just copied what I saw on Instagram, seemed to make perfect sense to me to just have one valve at the lowest point in the system.

 

The easiest way to eliminate your valves is to remove them and replace them with bits of pipe 

 

To be honest, down south, how rare are these edge case conditions that we fit these protection systems for? I can't remember the last time we had a power cut.

Edited December 6, 2022 by HughF

[SteamyTea]

35 minutes ago, HughF said:

I can't remember the last time we had a power cut.

Will be this winter now.

[ProDave]

Are you serious about valves to dump the water out of your system of it freezes?

 

I just mixed an inhibitor / antifreeze with the water in mine at a level that should prevent it from freezing to -10.  Job done.

[jack]

1 hour ago, HughF said:

I can't remember the last time we had a power cut.

 

I'm in the southeast and we get the occasional one - maybe once every year or two for 1-4 hours.

 

[HughF]

6 minutes ago, ProDave said:

Are you serious about valves to dump the water out of your system of it freezes?

 

I just mixed an inhibitor / antifreeze with the water in mine at a level that should prevent it from freezing to -10.  Job done.

At Caleffi prices, I wasn't going to bother, but for £16 from AliExpress I thought I'd fit one.