Balanced coverage?

[Mr Gus]

https://trade-chem.co.uk/25hr/e600-heat ... fluid-25l/
https://trade-chem.co.uk/5hr/htf50-heat-transfer-fluid/

How's this price? ..I can see how it mounts up by the 25% over 600 litres ratio mentioned, more so in colder operational areas.

[Countrypaul]

https://trade-chem.co.uk/25hr/e600-heat ... fluid-25l/
https://trade-chem.co.uk/5hr/htf50-heat-transfer-fluid/

How's this price? ..I can see how it mounts up by the 25% over 600 litres ratio mentioned, more so in colder operational areas.

I never looked at the price of the glycol needed, but can see it would not be an insignificant sum 150L @ £100/25L would be £600 + £120 VAT (I assume), even at £60/25L that comes to £442 (inc VAT) and how frequently does it need to be replaced?

[andygo999]

Hi Countrypaul

Thanks v much for describing your system to me, apologies for not replying sooner (been a manic few weeks).
With winter approaching we need to make a decision and pull the trigger on something soon....though I'm still undecided.

To be fair to the installers I've spoken to they've been pretty open and will connect a ASHP to the TS if we want (easier for them to do too). They just think the TS will be more expensive to run than a UVC. One who gave me some advice is actually based 500 miles away. I only contacted him because I'd read something he posted on another forum about how he connected his ASHP to a TS - he's regretting it now.

Here's what he said:

"My advice would be to ditch the store and get a heat pump cylinder which has a larger coil than a regular unvented for better heat exchange at lower temps.
"The problem I’m finding with my TS is the heat pump has to run on full rate to heat the volume of water inside. Once it’s up to heat it’s great because of limited heat losses. When I installed the system I thought I could substitute this for a buffer and have everything on one tank but it’s not quite as simple as that and a 45litre buffer would be far more economic.
"I’m going to swap mine out eventually.
"Go for a Vaillant aroTHERM plus as they have the best refrigerant and highest SCOP. Pair that with a 45l buffer and unistor cylinder."

I've read that having a UVC requires an annual service charge - I don't know if it's a DIY option - but I suppose that something to keep in mind.

Something I didn't quite understand from your post was this....

There are 2 TMV (thermostatic mixer valves) one at the top to mix the hot water from the top of the TS with water from the lower TMV. The lower TMV takes water from the middle of the coil (approx middle of the TS) and mixes that with cold water (if the middle is hot rather than warm). The idea is that this preserves the hot water at the top of the TS for as long as possible and limits the likelyhood of a TS full of lukewarm water.

I'm wondering how mixing hot water at the top of your store with cooler water below preserves the hot water at the top. I'd have thought it does the opposite and you do end up with a tankful of lukewarm water...obviously I've not understood properly.

Given the huge hike in electricity prices I'm not even sure if a ASHP is the way to go anymore - but we really don't want to install oil or lpg. Perhaps if we get some PV panels for summer electricity it will help offset the cost. PV will pay for themselves alot sooner now at least.

If we do keep the TS there's an immersion we can connect solar panel to - but it's in the bottom third of the tank so would be heating alot of water so not sure just how useful it is.

Perhaps the solar will be better off running the ASHP - but how much would I need to run a 7kw pump in Spring/autumn?

Thanks again for replying, do appreciate it

Andy

[Countrypaul]

Hi Andy,

With a TS that only takes hot water from the top (via a coil) you are always taking the hottest water and cooling the top of the TS. If you only want the DHW at say 60C and the take off is at 80C then you will take the 80C water and dilute it with say 10C water (cold supply) so you use 3-4L of 80c water with 1L of 10C water. The whole TS will be cooled by heating the 10C water to 80C. If the TS has a well stratified layering of water, lets for arguments sake just day 1/4 at 20C, 1/4 at 40C, 1/4 at 60C and 1/4 at 80C then to provide DHW at 60C the take off water from the TS will have entered at 10C, cooled the 20C water to n average of say 18C, the 40C water to 36C, the 60c water to 56C and the 80C water to 76C.

Now consider the TS with an additional take off in the middle, same stratification and same output requirement. Rather than mixing the 80C water with cold, it would be mixed with warm (40C water) so in this case you would need 1L of 80C water with 1L of 40C water to provide the 60c water, signifiantly less 80C water would be used. If the lower part of the tank gets sufficiently cooled than it would revert to working as the single take off conventional approach. If say 3/4 of the tank is at 80c, then the take off in the middle would be at 80C and mixed with 10C water to deliver 60C water to be mixed with the 80C from the top of the TS - in this case the top of the TS would not be used so leaving the top at 80C.

One complaint about thermal stores is they often provide a lot of luke warm water and no hot water - this dual take off scheme is supposed to minimise that. Hope my explanation has helped, you could probably do some maths for this second model and how the bottom of the TS will cool down quicker and the top slower than the conventional design.

Concerning your immersion heater you could look at a Willis heater which is an external immersion - which might give you an alternative option and still make use of you excess PV generation.

You could use the excess solar to run the ASHP depending on the functionality of your diverter. I have an eddi which is designed to allow this, you can set a minimum run time (to avoid excessive short runs) and a minimum amount of excess PV power before it will activate. If you have a 7kW ASHP with a COP of 3.5 you would only use 2kW. If you ASHP modulates down, then it might use less - I suspect you would have to try and work out by trail and error what the optimum settings are for your situation.

My understanding is that a UVC requires an annual service by a competant person (ie. one registered as such) and is therefore not a DIY option. In practice I suspect most do not get inspected annualy - no idea if house insurance is affected by that or not.

As to whether a UVC or a TS is the best option, I suspect that is not clear cut and will vary from installation to installation. If you have multiple heat inputs that can provide house heating such as a WBS then I would expect the TS to be more flexible. If you only have an ASHP and an immersion the UVC may be the simpler option that most plumbers are familiar with. If you could run the ASHP on E7 or other cheap rate electricity and heat the TS up enough to provide house heating during the more expensive electricty periods that might alter which would be more beneficial.

HTH

Paul

[andygo999]

Thanks again Paul

I'm not going to pretend I totally understand everything you wrote (failed O'level physics twice) but I think I get the gist.

I suppose for us it's going to boil down to what's most cost effective. The quotes we've had vary from £9k to £17k. The cheapest one is to simply connect the ASHP to the TS and bung in a few larger radiators. A couple of others were scared off by the Thermal Store to even bother quoting....

I've read up on Willis heaters - but hadn't thought about combining them with solar. Good idea, I may come back to you later to figure out a way of making it work.

I like the simplicity of the thermal store...but I worry it'll end up costing us more in the long term... the agony of choice eh?

[AE-NMidlands]

Another article:
https://www.theguardian.com/money/2021/ ... ng-outside (at-home-with-a-heat-pump-it-makes-hot-water-when-its-freezing-outside)

[Mart]

Great article and nice balance. Really shows the importance of matching the HP to the property and its needs.

Couple of issues I have though, the first example I thought was a bit misleading suggesting their PV covers the HP. I assume they mean that the PV generates as much or more than the HP consumes pa., but not that it matches the HP demand. Personally I think net generation is brilliant, as it shows that a home can be a generator/supplier too, I just think the article may be a tad misleading, and open itself up to negativity from the HP and PV critics.

In reverse, I thought the second example was interesting but also somewhat sad. It seems that an unsuitable HP was installed, and the customer praises one in his mate's home, that works great, but still refused the upgrade offered as he'd had enough. So an understandable negativity, wrapped in a personal bias to walk away due to past issues. There seem to be a lot of stories about folk getting 'burned' by inappropriate HP installs.

Perhaps, the important issue here is how much it is being stressed that a good match is made, and then the benefits that brings. If folk are encouraged to consider HP's, but also warned to make sure that the job is done well, then that's a really good balance to achieve.


My sister is now getting messed around with her install. She was originally told that a 3phase ASHP was more efficient, and she now has 3phase installed, and a 3phase PV system. Now the installer keeps trying to push a single phase ASHP, but that means that when there is spare PV, 2/3rds of it will be exported rather than reducing HP import. Anyone know if 3phase is more efficient? I've no idea why it would, but I know nothing!

[Tinbum]

I think 3 phase motors are more efficient than single phase but would have to check if that also applies to compressors. (Initial impulse is that it would).

[Tinbum]

Another article:
https://www.theguardian.com/money/2021/ ... ng-outside (at-home-with-a-heat-pump-it-makes-hot-water-when-its-freezing-outside)

Sounds like an advert for Mitsubishi to me.

[Bugtownboy]

Just a bit

I really have concerns that a lot of people will jump, because of the grant, and fall prey to poor installers or spiv salesmen. Likely both.

Surely the technology and functional understanding is there, it’s just going to be poleaxed by poor installations or householders who expect it to be a direct replacement for their combi.

I do wish there was a greater amount of control/direction from HMG, even if it’s only providing really tight guidance/regs/controls over the grant.

It’s disappointing, screw this up and we miss a great opportunity.