Heat Geek Series - Heat Pump Cylinders by Newark

Zarch · 2023-12-13T17:05:25.450Z

But before anyone goes diving in head first looking for a solution to their DHW woes, pause for a moment.

As i’ve found with my Mixergy cylinder. It’s rarely the cylinder that is at fault (as long as it is a proper heat pump cylinder with suitable coil). It’s how you use the heat pump to heat the water.

Ie Eco mode on Vaillant models.
The improvement i’ve seen moving from Normal mode to Eco in my setup has been eye-opening.

It appears this type of low compressor mode isn’t always available on some makes of heat pump, so swapping from your current 1.5sqm or 3sqm coil cylinder to a 6sqm Heat Geek one may yield next to no improvements.

I think it’s a case of watch this space.

Rachel · 2023-12-13T22:21:01.361Z

I don’t have a proper ASHP cyclinder, but I only run the ASHP to a set point of 43C because it will quite comfortably deliver that. In practice, 43C actually delivers 50C DHW at the top of the coil. If needed I top up with the immersion. Over the last month, my ASHP has delivered DHW with a CoP of 2.46 (and it’s been cold) and I’ve spend £6.00 on electricty for the immersion. In the summer I have solar thermal (though I’d ditch that in favour of more PV if I was doing it again) and solar divert from the PV, so the ASHP almost never runs for DHW. It’s hard to see how investing in a £2500 cylinder (installed) with something like a 60 year payback makes much sense. That’s the main reason I didn’t upgrade the original cylinder when I installed the heat pump (though the fact that it was almost impossible to get a solar ASHP cylinder at the time and I had a contingency plan to install my own external plate exchanger were also factors)

LeiChat · 2023-12-14T00:42:14.141Z

Almost. Opted for a Newark with 4m2 coil and 75mm insulation instead.

I am curious to compare the potential benefit of the larger coil (less kWh to re-heat) versus lower standing heat loss from a cylinder with thicker insulation.

gck303 · 2023-12-14T21:37:23.171Z

Somewhat gutted as this looks a great product. Wether it is worth the five hundred over the joule one is another matter, though.

We have just installed a 300l Joule cylinder. It works well enough. I did briefly consider the A+ rated OSO one, but could not get the energy savings to offset the additonal cost.

It takes 2 hours to heat to 52c. I have the flow rate set to 4 degrees above the tank temp at that time. Even when the tank reads 12 degrees we are still getting hot water out at 48.

Timbones · 2024-01-06T10:13:34.464Z

4 posts were split to a new topic: Waste Water Heat Recovery vs. COP

Timbones · 2024-01-13T21:20:55.482Z

5 posts were split to a new topic: Is Mixergy cylinder a good choice for heat pump install?

glyn.hudson · 2024-01-24T23:31:30.125Z

Zarch:

Intrigued to see who gets the first one of these installed on a openenergymon system and up on heatpumpmonitor.org

Adam’s got one! Or at least very similar, it’s impressive that over the past month including the cold snap he’s got a higher COP for DHW than he has for space heating!

Screenshot 2024-01-24 23.24.56932×797 255 KB

Here’s a link to his system on heatpumpmonitor.

Ringi · 2024-01-26T00:03:33.963Z

Does the very large coil makes a difference with Eco mode on Vaillant models, eg is it only important for heatpump that insist on using max output when in DHW mode?

The low insulation levels concern me as I assume I would only heat dwh on cheap rate so need to store a lot of heat.

KnightPhoenix · 2024-01-26T13:15:54.101Z

The same way that oversizing radiators allows the system to run more efficiently and push out more heat at lower volumes the bigger coil should have a similar effect (and can be seen on the system marked Mytchett, Surrey).

As these are custom built cylinders I expect there is not a lot stopping you asking for extra insulation provided you are happy to pay a little more for the extra materials.

While only heating DHW on the cheap tarrifs overnight is a great idea, provided the tank is inside the thermal envelope then any heat losses would be used to heat the house therefore not lost per say. With the COP at a Much higher level you could also run this during the day as with a COP over 4 it should easily be more efficient than any gas boiler.

If you are concerned about keeping the tank hotter for longer you could also look into WWHR as I am doing to reduce the hot water usage. It’s always better to insulate and reduce usage before going bigger.

Ringi · 2024-01-26T14:54:05.092Z

Assuming 7.5p kwh overnight and 30p kwh daytime, then any COP over 1 at night is better then COP of 4 in daytime! (But grant requires heatpump to be connected to DHW tank.) Heat loses from heating water in pipes between heatpump/tank in summer makes the true COP significant lower then the COP as measured at the heatpump. (In winter most of the pipe run is also used for radiators.)

This indicates that provided enough space the most important design aim for DHW is to have the capacity to store enough for a complete days usage regardless of how higher storage temperatures or larger tank reduces COP. Even if money is not an issue, spending it on batteries rather then custom tank may be better.

I would surport regulations requiring all new dwh tanks (including when connected to gas boiler) to have 6m^2 coils etc as then it would not increase cost much because mass macket tanks have many economies of scale with production/distribution.

matt-drummer · 2024-01-26T14:59:00.411Z

Those of us with proper metering do not take measurements at the heat pump, we take them where the tank and heating connections are, so the COP is true in the sense that it is the heat delivered to the tank and heating system.

.

KnightPhoenix · 2024-01-26T15:47:28.327Z

If you are going to be concerned with heat loss from the tank then surely you would use the batteries to charge up overnight and then heat the tank on a schedule to the lowest possible temperature just before needed (05:30am for a 6am shower) at ~40°c to 43°c, The lower the tank temperature the lower the heat loss from the tanks as it will take longer to dissipate. If you are happy with this and provided you can get another battery at a reasonable cost that totally makes sense.

Again adding in Waste Water Heat Recovery would likely cost around half the amount of the heat geek tank for the equipment (provided you can access the down pipe or under the shower/bath) and would reduce the volume of hot water needed so while not directly improving COP it would reduce usage.

It all depends on what you want to achieve and where you live. Do you want to be Top of the SCOPS, have the lowest running costs or be the greenest and lowest carbon house. While very similar these outcomes are likely to require three very different approaches and may all demand very different systems and priorities.

For southern England we usually have around 4 months where we do not need any heat so provided you heat your DHW in the middle of the day when it is hottest outside (so the heat pump has less work to do) you should get a good COP (but likely not as good as the heating) and as the surrounding environment is warm heat loss will be minimal, any solar panels will also offset the electricity costs (yes this will detract from your export fee but did you put them up to be a powerplant or to be green and use your own power?).

As matt has mentioned the heat meter from the L3 kit is sited within a meter of my DHW tank so the COP you see is what I am getting, however if your pipework is fully lagged and insulated I would be interested to know how large these significant heat losses are. Surely if the heat loss from an insulated pipe was that impactful then there would be more people installing an ASHP wall hung near the tank or moving the tank next to the heat pump and manufacturers would not have guidance allowing for 10m pipework runs. This would be quite simple to test and check but unfortunately I don’t want to put a heat meter outside on the back of the heat pump, especially when they are not particularly cheap and any comparison with other non MID meters would always introduce a bigger level of uncertainty due to the accuracy.

myatix · 2024-02-03T21:44:37.253Z

KnightPhoenix:

As these are custom built cylinders I expect there is not a lot stopping you asking for extra insulation provided you are happy to pay a little more for the extra materials.

That’s unfortunately not the case! I have had a long email correspondence with Tom from Newark and as soon as there are any form of customisations to these Newark models your looking at an additional £500-£1000 price tag!!?

The Heat Geek tanks themselves are over priced at present and customising a 300l cylinder will leave you out of pocket by over £2500. That’s going to take a hell of a long time to recoup if you ever will. As much as I would love to install one it just doesn’t make financial sense.

Bramco · 2024-02-04T10:38:48.903Z

Also, while the HG guys may have created an optimum design for ASHPs, there will be a lot of people out there with solar PV and if you have solar PV, then you’ll also have a diverter to do the DHW heating via an excess solar generation. And if you have a diverter, the optimum way of using this is with 2 immersions, one in the middle and one at the bottom. So you heat the top half first and when that’s hot start heating from below. From the specs, the HG tank has only one immersion, so to get the best out of solar PV diversion, you’re into a custom build and the tank as Alan says will be £2.5k.

We had a 300l unvented ASHP cylinder from Newark - 3m2 of coil area, with 2 immersions and some extra sensor pockets. From memory, it cost just over £1k - that was a couple of years ago. So let’s say £1.5k now. Considerably cheaper than the HG tank. It would be interesting to get a new quote from Newark for their standard unvented ASHP cylinder for a real comparison.

Simon

matt-drummer · 2024-02-04T10:46:37.111Z

Hi Simon,

I never understand why anybody with solar and a heat pump uses a diverter to heat water with an immersion heater.

Surely it is better to use the excess solar to run the heat pump to heat the water at an efficiency of more than 1:1, most heat pumps are over 200% efficient at heating DHW when it is warmer and sunny.

It is even better to import to run the heat pump, at a COP of over 2 for DHW in the sunnier and get paid at least 15p per kWh for the export.

Solar diverters are a waste of time and money with heat pumps as far as I am concerned if you are on a decent export tariff.

Bramco · 2024-02-04T11:05:17.267Z

matt-drummer:

Surely it is better to use the excess solar to run the heat pump to heat the water at an efficiency of more than 1:1, most heat pumps are over 200% efficient at heating DHW when it is warmer and sunny.

It is even better to import to run the heat pump, at a COP of over 2 for DHW in the sunnier and get paid at least 15p per kWh for the export.

Solar diverters are a waste of time and money with heat pumps as far as I am concerned if you are on a decent export tariff.

Hi Matt,

Using the excess energy to run the heat pump would - except for a day with wall to wall sunshine - mean that the heat pump would be taking energy from the grid as the sky clouded over. So there will almost always be 2 or 3kWs of import.

Also, with a diverter, you’re using whatever excess is available be it 100Ws or 3kWs.

On the tariffs, we’re on Octopus Go which is roughly 9p for the cheap night time rate and 30p for the daytime rate. We are also on the export scheme, so get 8p or so for export. So we’d be paying 30p to heat the water instead of using energy we’d be paid 8p for. If you are on a higher export rate then the comparison gets more favourable of course.

We may be a special case though, as the house is almost passiv haus, so with a 4 hour run of the ASHP on the nightime 9p rate, we’ve heated the house for the coming day. If we had the ASHP on heating as well as DHW, then we couldn’t be sure that the full 4 hours would be used for heating, so we run the ASHP in heating only mode. If we could force the ASHP into a particular mode for given time periods and we could get a better export tariff, then maybe we could switch off the diverter…

Simon

matt-drummer · 2024-02-04T11:19:44.522Z

Hi Simon,

If you use 2 or 3kWh of electricity to heat the DHW with the heat pump then of course that might be 6 to 9kWh of heat produced at a COP of 3 so you would actually use 6 to 9kWh of excess solar. 60p to 90p of import (if it all had to be imported) compared to 48p to 72p of export payments

In your case it is marginal I can see but for most of us I don’t think that is how we run.

If I imported at 28p on a tariff like Flux in the middle of the day and used 2kWh to produce 6kWh of heat with the heat pump my cost would be 56p and the 6kWh I exported instead of using on a diverter would get me about £1.20 of income.

If I don’t import as it is sunny enough/my batteries cover it and just use solar/battery it is even better as my 2kWh of lost solar exports cost 40p to get my 6kWh of heat that would have lost me £1.20 of exports using a solar diverter. (I have ignored battery losses in this statement).

For me, it is half to a third of the price to use the heat pump to heat DHW than it would be to use a solar diverter.

I think this is how it is for most of us but I accept that on your tariff and setup that it works for you.

Robert.Wall · 2024-02-04T12:01:26.277Z

Bramco:

100Ws or 3kWs.

Do you mean that? Ws = Joules?

KnightPhoenix · 2024-02-04T12:29:33.430Z

Just to interject and play devil’s advocate here.

I use the myenergi Eddi and have it set to run the immersion up to 500w (used to be 1kw with the dragon). As soon as I have over 500w of excess solar (and the powerwall is full) the relay board triggers the ASHP to run on the smart grid mode and boosts the DHW to 50°c, it will then overheat the house up to 24/25°c before stopping.

I get that using a standard PV diverter without the extra bits above is pointless but even with the EDLA09DA3V3 last year it was nice to know I was running fully off of locally produced green energy and the buffering means it didn’t run at night at all.

Obviously need to see how that will work out on the new unit now we actually have weather compensation working and don’t have to live in a sauna.

Timbones · 2024-02-04T13:00:09.884Z

Robert.Wall:

Bramco:

100Ws or 3kWs.

Do you mean that? Ws = Joules?

I’d guess that he meant “watts” (plural) rather than “watt seconds”.