Another 'Cool Energy' heatpumps thread

[HughF]

10 minutes ago, IanR said:

I can't see anything fundamentally wrong with your working, but...

 

Shouldn't you compare to a replacement condensing gas boiler at circa 90% efficient, rather than your existing non-condensing boiler?

 

 

75% efficient non-condensing gas boiler v. 350% efficient ASHP = 466.7% efficiency improvement

90% efficient condensing gas boiler v. 350% efficient ASHP = 388.9% efficiency improvement

 

7.9p per kWh Gas v. 28p per kWh electricity = 354% higher cost

 

Condensing gas boiler is still higher day to day running costs, but closer. 

 

If you already plan to replace the rads and cylinder, I'd go with ASHP as I view electricity costs to be more stable in the future. But if you only have to replace the rads for an ASHP install, and they will last 10 years, then perhaps another gas boiler is the better cost option.

It's basically a full CH system rip out and upgrade that I'm planning.

[IanR]

10 minutes ago, HughF said:

I think I could DIY the ASHP + UVC + rad upgrade for about £5k, 

 

Then your comparison is more likely a self-install ASHP for £5k v. an MCS ASHP install for £?K with a £5K BUS grant and a 7 year warranty. (Unless ASHP manufacturers will now give full warranties on a DIY Install.)

If you can find a friendly MCS firm, perhaps you can do the UVC, rads and most of the copper and brass and the MCS company do just the ASHP.

Edited April 20, 2022 by IanR

[HughF]

1 minute ago, IanR said:

 

Then you comparison is more likely a self-install ASHP for £5k v. an MCS ASHP install for £?K with a £5K BUS grant and a 7 year warranty. (Unless ASHP manufacturers will now give full warranties on a DIY Install.)

If you can find a friendly MCS firm, perhaps you can do the UVC, rads and most of the copper and brass and the MCS company do just the ASHP.

I was just doing a running costs analysis really, that's what's important for us moving forwards...

 

[HughF]

Thinking more about the dhw requirement, and having watched the RED heat pump introduction on freedom heat pumps YouTube channel, and seeing that they use an open vent TS for their dhw, has got me thinking.

 

has anyone successfully done dhw with air source using a (large) plate heat exchanger directly on the flow and return loop, standard thermal store style, using a flow sensor and a shunt pump?

 

Edit: now I think about it, this won’t work at all. The stored energy in the TS water is required to cover the instantaneous demand of the plate heat exchanger. No way that can be taken from the flow/return loop directly and instantaneously.

Edited April 22, 2022 by HughF

[ProDave]

You don't want a thermal store with a heat pump.  For a TS to have any capacity, it needs to store the water a lot hotter than the delivery temperature, which is completely the opposite of what you want to do with a heat pump.

[dpmiller]

I've gone for the TS/ ASHP and I contend it works perfectly well as long as you have the probe position correct and have a sufficiently large coil. Plus there's the possibility of other inputs like a boiler stove.

 

in actual fact I've gone direct for the stove, and indirect for the ASHP.

[ProDave]

43 minutes ago, dpmiller said:

've gone for the TS/ ASHP and I contend it works perfectly well as long as you have the probe position correct and have a sufficiently large coil

What temperature do you heat the water in the TS to with the ASHP?

 

With our UVC we heat it to 48 degrees.  I strongly suspect if you only heated a TS to 48 degrees, you would not get much water out before the temperature was no longer hot enough.

[dpmiller]

I heat the tank (from the coil at the bottom) til the probe at the middle is 52. During this process the flow temp will be a few degrees higher so the top of the tank might be as high as 57. The DHW coil is above this probe.

 

But when the heating is running, the flow temp is 42  and this continually buffers energy into the bottom of the tank (or extracts it if the sun's been out during the day, say.

 

With a 9kW heat pump and a nice big coil, the system seems happy to recover during and/or after showers, without the DHW falling far enough to upset the shower mixing valves.

Obviously if the sun's out the diverter can have the whole tank up to 90c, but it starts on the upper immersion so the top of the tank only rarely needs to be actively heated by the ASHP anyway...

[JohnMo]

You could also directly charge the thermal store from the heat pump or go via a plate heat exchanger.  If you used a plate DHW exchanger, you may get better heat exchange and able to use full contents of TS or part charge it in low use situation.  Advantage is no possibility of short cycling during heating as this would be fed direct from from thermal store.

[HughF]

All good discussions, thanks…. I figured that a plate heat exchanger running the dhw from a 55 deg TS would be ‘enough’. Perhaps I should play with this. Trying to maximise cupboard space and minimise short cycling whilst giving enough hot water .

 

@dpmillermay I enquire what brand of ashp you’re using?

Edited April 23, 2022 by HughF

[dpmiller]

2 hours ago, HughF said:

 

@dpmillermay I enquire what brand of ashp you’re using?

 

Cool Energy...

[HughF]

8 minutes ago, dpmiller said:

 

Cool Energy...

The 9kW inverter one?

[dpmiller]

18 minutes ago, HughF said:

The 9kW inverter one?

yep. I've some info in my build thread

[HughF]

Dragging this thread into May, I’m thinking about thermostats.

 

The cool energy unit uses a carel controller (which seems to be designed for a commercial fridge) which supports programmable flow temperatures for either dhw or ch. These temps can be fixed or have a 4 point weather comp curve. This controller also supports numerous on/off timed programs. All good there.

 

The controller doesn’t know or care about room temperature, it just reads two probes, one for buffer/llh temp and one for uvc temp.

 

So I’ll need some sort of room stat, at least until I get the weather comp dialled in perfectly. Ideally I’d like one that has programmable upper and lower limits, the lower limit being the most important, so that a nighttime setback isn’t set too low by accident. At the moment we have an old Honeywell mechanical stat in the hallway (a stupid place really as the hallway radiator is massively undersized).

 

What are my options for a good, simple to use, programmable stat that will work without a cloud provider account/internet access?

[Marvin]

40 minutes ago, HughF said:

Dragging this thread into May, I’m thinking about thermostats.

 

The cool energy unit uses a carel controller (which seems to be designed for a commercial fridge) which supports programmable flow temperatures for either dhw or ch. These temps can be fixed or have a 4 point weather comp curve. This controller also supports numerous on/off timed programs. All good there.

 

The controller doesn’t know or care about room temperature, it just reads two probes, one for buffer/llh temp and one for uvc temp.

 

So I’ll need some sort of room stat, at least until I get the weather comp dialled in perfectly. Ideally I’d like one that has programmable upper and lower limits, the lower limit being the most important, so that a nighttime setback isn’t set too low by accident. At the moment we have an old Honeywell mechanical stat in the hallway (a stupid place really as the hallway radiator is massively undersized).

 

What are my options for a good, simple to use, programmable stat that will work without a cloud provider account/internet access?

My heating pump is on a programmable thermostat. The ASHP heats the buffer to the set temperature.

[HughF]

46 minutes ago, Marvin said:

My heating pump is on a programmable thermostat. The ASHP heats the buffer to the set temperature.

I'm going to try and get away without a buffer and just use an LLH, as I'm short of space. Really short of space...

[JohnMo]

Before you run weather compensation, you will need to balance the system.  Then run a single high limit stat, and use and tweak the system flow temps, so you get the temp you want without the thermostat kicking in at anytime. It is normal to run weather compensation 24/7 with only a 2/3 degree setback at night if you want.

[HughF]

1 minute ago, JohnMo said:

Before you run weather compensation, you will need to balance the system.  Then run a single high limit stat, and use and tweak the system flow temps, so you get the temp you want without the thermostat kicking in at anytime. It is normal to run weather compensation 24/7 with only a 2/3 degree setback at night if you want.

It's the programmable setback stat that I'm looking for - I want that to happen automatically at a preset 'bedtime'.

[ProDave]

43 minutes ago, HughF said:

It's the programmable setback stat that I'm looking for - I want that to happen automatically at a preset 'bedtime'.

Any programmable room stat should do that.  You don't set on or off times, you set what temperature you want at what time of day, so you set your daytime period to one temperature and the night temperature a few degrees lower.

[HughF]

52 minutes ago, ProDave said:

Any programmable room stat should do that.  You don't set on or off times, you set what temperature you want at what time of day, so you set your daytime period to one temperature and the night temperature a few degrees lower.

Understood, thanks. I’ve seen some units from salus that appear to do just what I want.

[JamesPa]

A philosophical question here - having gone to the trouble of getting weather compensation right, isn't it better (ie more efficient) to set back the flow temperature at night rather than using a roomstat to effect night time set back.  The latter just causes the HP to switch on and off periodically but keeps the flow temp high, whereas reducing the flow temp achieves the same result as far as the house is concerned but improves COP.

 

Of course not all controllers implement this function (see incomplete discussion here):

 

but I have heard of people faking the behaviour (admittedly in a different context) by switching a fixed resistor in and out of the outdoor temperature sensor circuit, to fool the unit into thinking the outdoor temperature is different than it actually is.

 

 

 

 

 

[HughF]

13 minutes ago, JamesPa said:

A philosophical question here - having gone to the trouble of getting weather compensation right, isn't it better (ie more efficient) to set back the flow temperature at night rather than using a roomstat to effect night time set back.  The latter just causes the HP to switch on and off periodically but keeps the flow temp high, whereas reducing the flow temp achieves the same result as far as the house is concerned but improves COP.

 

Of course not all controllers implement this function (see incomplete discussion here):

 

but I have heard of people faking the behaviour (admittedly in a different context) by switching a fixed resistor in and out of the outdoor temperature sensor circuit, to fool the unit into thinking the outdoor temperature is different than it actually is.

 

 

 

 

 

That’s exactly the way it should be done, yes… how one does that in practice, with the units in my price range, I don’t know (yet)

[JamesPa]

Interrupting the outdoor sensor and switching in a fixed resistor on a timer is cheap and easy, albeit a 'kludge'.  A friend of mine did this with a gas boiler to fix up a problem with weather compensation (basically his stupid Worcester Bosch boiler supports weather compensation but applies it even when heating the DHW, so he has switched in a fixed resistor to defeat the weather comp during the times DHW is being heated)

 

It's better to find a more elegant way though if there is one!

Edited May 5, 2022 by JamesPa

[ReedRichards]

I use a night time set back on my thermostat but unless it's very cold out this just has the effect of turning the heat pump off completely; there would not be any need to set back the flow temperature and keep the heat pump running.  During the day I ramp up the set temperature on my thermostat; something I have been doing for the last 25 years and long before I had a heat pump.    

[dpmiller]

the Coolenergy controller will happily run variable flow temperatures at different times of day, the four timeslots have programmable setpoints for all three modes. Weather comp then "adjusts" these numbers.

 

Plus the fan modes (high/low/night/pressure) alter the compressor's max speed too.