Looking for a cylinder/thermal store for Solar PV and Eco7/electric only for DHW and wet UFH

[Susie]

I didn’t think this would be so hard but after speaking to Telford they said it doesn’t work they have no cylinder that can be run like this. Telford also said constant on/off is not good for immersion heaters, they wouldn’t last as long, and they said thermal stores are outdated, now better insulation is available for cylinders.  He seemed to think I need a boiler or heat pump but I disagree.  Im working on getting my U value for the new build low to avoid heating most of the year.

 

Spoke to another supplier of UFH and cylinders who looked into it then rang back and also said it can’t be done

 

Next I contacted Gledhill they suggested the Torrent stainless OV

 

https://www.gledhill.net/products/alternative-energy/torrent-stainless-ov/

 

I also contacted cylinders2go who thought a cylinder with a heat exchanger would work and suggested I ask on the forum.

 

Im sure a lot of users on the forum are doing something similar so why am I running into problems?

 

Other alternatives are willis heater and  Sunamp.  I don't know much about Sunamp so more research needed.

 

 

I have been using the fabric and ventilation heat loss calculator and the floor heat loss & UFH calculator.  Here is my summary.

 

[JohnMo]

I think the problem is although only 1345W that's 32kWh per day.

 

E7 would be 4.5kWh per hour for 7 hours.

 

PV is pretty rubbish in the winter, so I wouldn't bank on anything spare for heating in the winter. But in the summer most of your DHW would be PV heated.

 

Think I would seperate DHW and UFH.  Exhaust air heat pump cylinder for DHW, route the air from outside and back outside.  Then a Willis x2, most of time only one required.  Then batch charge the floor on E7.

 

Or joules do a slightly bigger exhaust air heat pump that can do central heating also.

[Nickfromwales]

8 minutes ago, JohnMo said:

Think I would separate DHW and UFH

There's not much to think about, you'd just separate them as they're 2 very different things in a PH. DHW still needs a decent bit of welly, but heating, then, only a thimble ( or 2 )

I've worked for a couple of turnkey M&E clients who insisted on no heat-pump, and with the way electricity costs are going I bet they will soon live to regret there stubbornness.

If you have a LOT of PV you can "consider" your options. In the 3 months of winter you'll expect 25% solar irradiance or less, ergo a 10kWp array will deliver 2.5kW or less in winter. IF you are able to channel that into a heat pump, which is an energy multiplier, even in winter, you could then look realistically at offsetting the heating demand from onsite microgeneration. That is based on first considering watt the base loads are for the dwelling and summarising on the averages left over that would contribute to space heating. Without the heat pump........forget about it. Your best friend then will be simply dumping cheap rate electricity into the heat pump and charging the slab like a storage heater.

All entirely academic of course, as any excess PV would be long gone on winter DHW.

Fit a heat pump. You'll be kicking yourself if you don't.

 

[Radian]

4 hours ago, Susie said:

Telford also said constant on/off is not good for immersion heaters, they wouldn’t last as long

 

OH NO! I'm doomed then. Mine goes on and off 50 times a second!

WTF are they on about?

[SteamyTea]

5 minutes ago, Radian said:

WTF are they on about?

They may be on about thermal cycling.

If the element is on for 60 seconds, then off for 120 seconds, then on for 60, then off for 120 i.e. mimicking 1/3^rd of the output potential, then it may shorten the life.

Would be a strange setup then did that though.

[ProDave]

1 minute ago, SteamyTea said:

They may be on about thermal cycling.

If the element is on for 60 seconds, then off for 120 seconds, then on for 60, then off for 120 i.e. mimicking 1/3^rd of the output potential, then it may shorten the life.

Would be a strange setup then did that though.

Mine routinely turns on and off twice per second (not as fast as @Radian system)  It's called "burst firing" meaning the on time is adjusted in this case to match available power. And Burst firing is used for industrial heater power control e.g in a furnace.

 

You would have thought if such burst firing was detrimental to the life of a heating element, it would be well documented?

[Susie]

That’s my problem @Radian@SteamyTeawhen they say something so stupid and he was talking minutes on and off because I questioned that.  

I was getting told no cylinder is set up for PV input and UFH output not that I shouldn’t do it for cost or any other reason just that it can’t be done except Gledhill.
 

 

[Susie]

I haven’t totally crossed of a Heat pump but I’m only a few miles from the coast on top of a hill and in winter we can have sea mist come and go a lot. 
we get strong winds from 3 directions because we’re so exposed. 
I’m concerned how quickly a heat pump could deteriorate in the salty air. 
 

 

Edited November 11, 2022 by Susie

[Radian]

 

14 minutes ago, SteamyTea said:

They may be on about thermal cycling.

If the element is on for 60 seconds, then off for 120 seconds, then on for 60, then off for 120 i.e. mimicking 1/3^rd of the output potential, then it may shorten the life.

Would be a strange setup then did that though.

 

This does seem to allude to thermal expansion of the nichrome heating element and encapsulation materials. Cycling in the order of minutes is commonplace in oven and grill elements. Burst firing is somewhere in-between frequency wise so between milliseconds and minutes the extremes seem to be covered. I'll do an autopsy on mine if and when it fails but I'm not expecting that to happen in my remaining lifetime.

 

[billt]

8 hours ago, Susie said:

I’m concerned how quickly a heat pump could deteriorate in the salty air. 
 

 

The decent heat pumps will have the option of some sort of extra protection for salty areas, although, if your several miles from the sea it shouldn't be that much of an issue.

 

For instance, the Grant manual says

 

" When installing the heat pump where it may exposed to strong
wind, brace it securely.
• If the Aerona³ heat pump is to be installed within 1 mile of the
coast, avoid siting facing the sea.
• If the Aerona³ heat pump is to be installed within 2 miles of the
coast, the evaporator must be sprayed with ACF50 and this
must be repeated on each service, unless a factory supplied
‘Blygold’ Aerona³ heat pump has been installed."

 

" 3.10 COASTAL INSTALLATIONS
Heat pumps installed in coastal locations are prone to corrosion
damage due to exposure to the sea air.
Corrosion of the aluminium fins and copper tubes of the evaporator
can reduce the output and limit the lifespan of the unit. To prevent
this happening for all installations within 2 miles of the sea Grant
recommends using an anti-corrosion treatment.
Two possible options of anti-corrosion treatment are available for
the Aerona³ range of heat pumps.

Blygold coating
All Grant Aerona³ air source heat pumps are available in a Blygold
treated version. This involves a factory applied corrosion protection
coating of the evaporator. This MUST be specified when ordering
the unit as it is NOT available as a retro fit option for on-site
application.
The coating applied to the evaporator (Blygold PoluAl XT) is
polyurethane impregnated with aluminium. Once applied it seals
the dissimilar materials of the evaporator from the atmosphere to
protect it from the marine environment.
This coating is water repellent, helping to prevent dirt adhering to
the evaporator fins that could reduce the heat pump output. As with
any such evaporator, it must be periodically cleaned to maintain the
benefits of the coating and maintain the efficient operation of the
heat pump.
Refer to Section 10 of these instructions for further details of the
servicing requirements.

ACF50 coating
This is a retro fit option that is applied to the evaporator on-site.
the outer casing of the heat pump will have to removed for the
evaporator fins and tubes to be sprayed from both sides. Refer
to the instructions supplied with the ACF50 for more detailed
information on the application procedure.
Originally developed for the aerospace industry, ACF50 is a
hydrocarbon based anti-corrosion compound that forms a selfhealing barrier on new metal. It is an ultra-thin fluid film that dispels
any moisture (including salt water) already present and provides
an atmospheric barrier preventing any further moisture coming in
contact with the surface in question.
It continues to creep into narrow gaps, seams, etc. providing
protection for 12 months and thus must be re-applied on an annual
basis to maintain the level of protection. Refer to Section 10 of
these instructions for further details of the servicing requirement."

[SteamyTea]

8 hours ago, Radian said:

I'll do an autopsy on mine if and when it fails but I'm not expecting that to happen in my remaining lifetime.

And we can do an autopsy on you, if you like.

 

Just to be clear, I don't think element cycling is a problem, though it used to be with car indictor bulbs, they always lasted less time than headlight bulbs.

 

9 hours ago, Susie said:

I’m only a few miles from the coast

Down on the seafront at St. Ives, there are dozens of ASHP, usually to cool beer, they are very exposed and none seem to be showing bad corrosion.

[Gone West]

14 hours ago, Susie said:

 Im working on getting my U value for the new build low to avoid heating most of the year.

We had very low U values in our PH. We heated the DHW with an EASHP which was built into the MVHR system so also provided warm air through the ventilation. The house was heated with three towel rails in the bathrooms. I designed the house so no conventional central heating system was required. We ran the whole house at 23C 24/7.

[Radian]

5 minutes ago, Gone West said:

I designed the house so no conventional central heating system was required.

 

To what extent did you factor solar gain into the design?

[Susie]

I will look into an EASHP thanks @Gone West .  I’ve not got as far as choosing the MVHR, no quotes back yet so also left the spreadsheet at air changes per hour at .43 and MVHR efficiency at 85% so hopefully this can be improved. 

I’ve read about the extra coatings they can put on the ASHP @billt but still not convinced my outdoor investment is the best way I can spend my £ it’s the insides of all those ASHP further down the coast I’m thinking about the average life span of an ASHP in salty conditions can be as low as 7 years in which case my investment is better else where.  Perhaps all those air BNB and second homes can afford the maintenance costs or they don’t know until it’s gone wrong and the installers don’t care as that’s more income when they go back to fix them for the part that is out of warranty. 🤔

im considering putting the UFH in but not connecting it up to anything until I know I need it, leaving room in the plant room for either a Willis heater or looking at the Sunamp system. 
 

 

[Susie]

@Gone West was EASHP a typo, a quick search finds EAHP

 

[Gone West]

3 hours ago, Radian said:

 

To what extent did you factor solar gain into the design?

We had a double glazed porch 3m x 1.5m which we used for solar gain. It faced ESE and proved very useful in the spring and autumn as we simply opened the hall door and had free heat. In the summer we used reflective blinds in the porch which we kept closed all the time.

[Gone West]

3 hours ago, Susie said:

@Gone West was EASHP a typo, a quick search finds EAHP

 

No, our system used the EASHP to use the heat recovered from the MVHR. There are standalone DHW cylinders that utilise a dedicated air to water heat pump to provide hot water.

 

https://www.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html

 

[Nickfromwales]

The advice around cylinders vs space heating is sketchy at best because the two never really go together. Issues mostly surround the transfer ( linear ) of energy, from electricity to heat, which is normally combatted by multiples of 3kW immersions or specifying 6kW immersions and so on.

Eveything changes hugely in a PH though, and then you can basically tear up the rule book and do some “less than conventional “ designs to suit your own ( almost unique ) circumstances.

That reduces the issue I state above, but that doesn’t go away if you need to heat a lot of water in a short ( off-peak ) window. 
Prob with the Sunamp ( aka Thermino ) is the inherent single 3kW immersion. Ergo that can only ever absorb / transfer energy at a relatively slow rate, sometimes it was not enough and designs / proposals failed miserably.  

They’re also now just so ludicrously expensive ( ‘bespoke’ supply and fit packages only ) vs an UVC that it really doesn’t make good financial sense to go with SA, unless you have very limited plant space / zero plant space where these can fit under a kitchen / utility worktop. Just about the only USP nowadays with a SA.