Calculate ROI for a custom Unvented Indirect Heat Pump Cylinder???

[myatix]

I am considering using a custom built heat pump cylinder with a dual coil setup to maximize the heat transfer from Heat Pump to the DHW Cylinder. Ideally you want to run a heat pump at as low a flow temperature as possible to maximize the SCOP. Therefore having a custom cylinder with 6m2 of coil vs the standard 3m2 for most heat pump cylinders would allow for much lower temperatures and a lower flow rate therefore optimizing's the energy transfer.

I have had a few companies provide a quote for this type of cylinder but I would like to calculate the return of investment to see if it is financially viable over a 5-10 year period.

The tank with the 28mm, 6m2 coil is double the price of the 28mm, 3m2 coil so I am not sure it is worth it...

I look forward to hearing from anyone who might be able to help?

 

[Notch7]

I am just replacing my ancient gas boiler with a new condensing gas boiler with a hot water priority set up and weather compensation

Given that the engineer is taking out the hot water cylinder to fit all the new pipework and controls, I decided to have an ultra fast recovery cylinder, but as its just a 117 litre vented jobbies its only £500 so Im just doing it as part of the package and not worrying about ROI

I imagine your cylinder might be a lot more money, so its rather different

In terms of ROI, I guess you need to consider the price of energy in the future as that could have a big bearing on ROI

have you looked at off the shelf unvented cylinders with vacuum panel insulation and fast recovery coils?

ARE HOT WATER CYLINDERS CREATED EQUAL?

Stuart Elsy looks at the features to look out for and what installers should consider to ensure they are recommending the best.

osohotwater.co.uk

 

[muggles]

I think the Newark HG cylinder is what you're looking for

 

[myatix]

@Notch7 Thanks for the response!

Yes I need a 250-300L DHW Indirect Cylinder... and as it is for a Heat Pump I need to ensure that the coil is super efficient and as long as possible.
I have a custom design with 6m2 of corrugated 28mm coil pipe

 

[myatix]

I think the Newark HG cylinder is what you're looking for

Yes… The Heat Geek Cylinder does sound like a good solution but with a price tag of over £2500 plus £120 for delivery for a 280L unvented indirect cylinder it’s far, far too expensive compared to other DHW Heat Pump Cylinders that usually sell for half the price. This is especially true when there is no data to prove that the additional investment would ever be financially viable.

As far as I am aware there is only one of these cylinders in use today (By the guy who designed it) and that isn’t really a viable test considering it’s being tested by the people who designed and built the cylinder.

What will be interesting however is to see what other competitors produce to compete with this offering as the current asking price doesn’t match the production cost of adding an additional 3m2 of coil to the cylinder.

 

[muggles]

What an odd response. Are you saying you believe your own design will do a better job and cost less than one designed and built by industry experts? It's a bespoke product produced in low volumes which requires bespoke tooling & jigs - far more than just chucking a bit more coil into a cylinder.

Have you tried McDonald Engineering to see if they will produce a cylinder to your own specification, if that's what you want?

 

[myatix]

@muggles No that’s not what I am saying! What I am saying is that the Newark HG product appears to be very over priced based on the lack of data to backup the cost of the product.

I can appreciate the initial cost is higher when designing a new cylinder but like any other product development process costs are regained over time, not by over charging the first customers. Jigs and tooling only need to be created once and can then be reused for all additional orders, hence recuperating initial investment cost as time goes by.

If someone can show the investment is financially viable then I would love to see the data for that.

It’s a great idea but I’m sure others can build a very similar product for a lot less. The design has similarities to a Heat Pump/ Solar cylinder which is a popular solution from multiple cylinder manufacturers today. Let’s see perhaps someone will share some performance data at some point?

I will have a look at McDonald Engineering… Thanks!

But back to the question at hand… How would you calculate the performance difference between 3m2 vs 6m2 of coil. I doubt there is a doubling in performance?

 

[robinbanks]

you want to run a heat pump at as low a flow temperature as possible to maximize the SCOP

But if you want to use an HP to heat a tank of water to 55 degrees, you're going to have to ask it to produce 55 degrees so where are you getting this "must be low flow temp for efficiency" idea from? Doubling your coil area ain't going to make it possible to get a 55 degree tank from a 35 degree flow. Low flow temps are for space heating, not DHW; sounds to me like you're mixing up CH and DHW or you're missing the point that the coil should be suited to generating a temperature difference between flow and return that is well suited to what the ASHP wants to work with. My ASHP wants a 7 degree difference and the 3sqm coil will do that at the flow rates the pump uses.
Has your ASHP manufacturer said the unit needs a 6sqm coil?

 

[myatix]

Doubling your coil area ain't going to make it possible to get a 55 degree tank from a 35 degree flow.

@robinbanks Yes I do realise that! However having double the surface area will speed up the reheat time so I can run the heat pump at a lower temperature and get a faster heat up rate. Looking at Vaillant’s heat up time for a unistor 300 you are looking at 48min. at best. Presumably this is running the heat pump at maximum capacity at 75 Degrees.
To optimise the SCOP you want to keep the temperature as low as possible with as small a DT as possible so by using a larger coil your slowing the flow rate down and improving the thermal transfer. Plus the heat pump doesn’t suddenly need to run at full wake for 48 minutes and therefore reducing your electricity consumption.

 

[robinbanks]

by using a larger coil your slowing the flow rate down

Hmm, yes.. That's exactly how it works (not!)

But crack on, the only thing you're really going to harm is your wallet..

 

[myatix]

Okay... Perhaps you would like to explain how it does work if dT and Flow rates have nothing to do with energy consumption???

https://en.wikipedia.org/wiki/Mass_flow_rate#cite_note-7
Mass flow rate can be used to calculate the energy flow rate of a fluid:

where

is the unit mass energy of a system.

Heat Geek - Explanation of Mass Flow Rate and the relationship to Energy.

See page 33 (5.2.2 Heat Losses)
https://projekter.aau.dk/projekter/files/250488225/00_REPORT.pdf

Hmm, yes.. That's exactly how it works (not!)

But crack on, the only thing you're really going to harm is your wallet..

@robinbanks It would be nice if you could share why you don't think it works like that rather than being sarcastic and share your knowledge with everyone.

 

[myatix]

I just wanted to share some very relevant information for others that may read this article and be interested in how they can optimism their DHW Cylinder for an Air Source Heat Pump.

The following is an article based on the open energy monitor community that has a wide community of users who collect and share data based on their home setup.

The article specifically shares the difference in performance when using Newark's HG (Heat Geek) Cylinder vs a Mixergy and other Cylinder Manufacturers, such as Telford and Joule.

https://energy-stats.uk/mixergy-heat-pump-performance/

This provides a great comparison between the energy efficiency of different types of cylinders and how the dT and Flow Rate significantly impact your energy consumption based on data that has been collected over a long period of time.

I hope you find this useful...

 

[Notch7]

Therefore having a custom cylinder with 6m2 of coil vs the standard 3m2 for most heat pump cylinders would allow for much lower temperatures and a lower flow rate therefore optimizing's the energy transfer

Are you sure that is true?

if the coil is too long the temperature near the end of the coil will end up the same as the hot water temperature.

im not even sure there’s a linear relationship between coil area and heat transfer.


I think your calculation will be heavily influenced by your real world usage of hot water.If for example your usage is heaviest at morning and evening and none during the day, Imwouldve thought standing loss would be more important the heat transfer in the coil.


I don’t know the specs of the cylinders you are looking at but heat transfer is more efficient with copper than stainless steel. Then there’s finned coils and multi tube coils etc.


Personally I can’t see your ROI being anything sensible

 

[myatix]

@Notch7 With OpenEnergyMonitor.org you can actually go in and view the stats on a Cylinder. Adam from Heat Geek has shared all of his data online since June 2023 so yes I am very sure...

Heat Geek Newark Cylinder Install

Newark Heat Geek Cylinder statistics for 4 person family (6 months)

Emoncms - app view

emoncms.org

Interesting comment with regards to copper vs stainless... but that is why Newark use a high efficiency coil I guess.

As for the coil length coils are plumbed in parallel, so it is not just 1 long coil but 2 standard length coils... (See YouTube video above for details)

 

[Notch7]

@Notch7 With OpenEnergyMonitor.org you can actually go in and view the stats on a Cylinder. Adam from Heat Geek has shared all of his data online since June 2023 so yes I am very sure...

Heat Geek Newark Cylinder Install

Newark Heat Geek Cylinder statistics for 4 person family (6 months)

Emoncms - app view

emoncms.org

Interesting comment with regards to copper vs stainless... but that is why Newark use a high efficiency coil I guess.

As for the coil length coils are plumbed in parallel, so it is not just 1 long coil but 2 standard length coils... (See YouTube video above for details)

thanks I shall have a watch of that video later when Ive got time.

Im just in the process of replacing my gas boiler and am having a ultra high recovery cylinder to help the hot water priority configuration.

I find this stuff really interesting -its surprising that UK has had condensing boilers for years but most of them fitted dont run in condensing mode....people like heat geeks and Urban plumber are leading the way on this


I expect if you are in Denmark, the industry is far more ahead on heat pumps / hot water priority etc