Noticing this, I wondered about the use of the invisible ‘space’ character after ‘comb’, thus 'comb '. I’ve just tried it, by searching for ‘comb heat pump’ instead of your ‘heat pump comb’ and got this which may be of interest. It led me to this Rothenburger one, but others are no doubt available. ‘Fin comb heat pump’ or ‘lamella comb heat pump’ seem to be alternative search terms worth trying too. But maybe you’ve already found one or have found a different solution.
The Rothenburger one looks like a better quality version of the one I got. I discovered that I should be searching for “air conditioner fin comb“.
I haven’t used it yet as I’ve been putting extra insulation on the pipes first. I am concerned that repeated flattening and straightening might weaken the metal, so I’m waiting until all work behind the unit has been finished.
See also
I’m unclear on ‘cylinder’ versus ‘buffer cylinder’. Have I got this right:
- the buffer cylinder is like a storage system, to prevent short-cycling; it’s downstream of the HP, obvs, and is directly connected to the space-heating circuit; typically ~100ltr capacity
- the domestic hot water cylinder is connected to the water mains, obvs; it’s further downstream of the space-heating circuit and is heated (via heat-exchanger) by that circuit
- the DHW cylinder also has its own electric heater (resistive/grid, or otherwise), so it can reach required DHW temps, and also so it can ensure ‘potability’, ie prevent Legionnaire’s etc; typically 150ltr+
That about right?
Roughly speaking you’ve got it. My buffer tank is only a few litres and serves as a dissassociation between the heat pump circuit (near constant temperature, high flow rate) and radiator circuit (widely variable temperature, low flow rate). The two flows mix in the tank, rather than having a heat exchanger/coil.
Potable = “safe to drink” (Latin) and whereas drinking Legionella simply adds minuscule amounts of protein to your diet, breathing it in can cause pneumonia. The sterilisation is to render any spay of water safe.
I’m not convinced that it works 100% as your hot water is mixed with cold that hasn’t had the same treatment and will contribute to any spray.
I’ve re-read this and realise I need to disagree.
The hot water cylinder is not downstream of the heating circuit but a T-off before the first radiator. There is a 2 way valve where the branching occurs. With a boiler the options for the valve are “open open”, “open closed” and “closed open” to allow the hot water in the circuit to flow to either or both branches but in a heat pump circuit there is no “open open” option. A heat pump will run the DHW branch at a higher temperature than the heating branch and therefore needs to limit flow to the appropriate branch. This is why heat pumps cannot provide heating at the same time as hot water. Your house needs to retain heat for at least as long as it takes to heat the water.
Ahh right. Thanks. Therefore you typically control the diversion of HP heat to the DHW cylinder via a timer or some such? - ie, with a HP, DHW is no longer on-demand, like with a gas combi-boiler; instead, the time of demand needs to be set, ahead of use. I’m actually considering using a thermal battery to store heat for DHW (more expensive, but a lot less bulky); do you know if this produces more of an old-style on-demand situation for DHW, provided of course that the thermal battery has been ‘charged up’?
I think you need to define “old fashioned”. When I was a child most homes had a hot water cylinder which was heated by various means. Ours was via an oil boiler. To me the old fashioned way was that there was no correlation between demand for hot water and the time that it was heated.
That is what we are returning to now. We heat the water when convenient or cheap and use it when we feel like it.
You’re right, I remember such set-ups, our cylinder of days gone by was anthracite-powered… Was wondering if a thermal battery has the edge on a DHW cylinder, no matter how well-insulated the latter may be? ('Spose I need to start a thread to see if anyone on here uses such a battery.)
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do you rate the Daikin heat pump? This is the one that Octopus are installing. Most people around me are putting in the Vaillent AroTherm. I am just starting to research which one will be the best for me to fit, as well as who is best to fit it.
@Lorrie_Marchington, welcome to the forum.
There isn’t much difference between different quality models of low temperature heat pumps (HP). First consider the maximum output of the unit and find models that meet your requirements. The ranges of models do not directly correspond with each other, so that will filter out some options.
What makes the biggest difference to performance and running cost is the quality of the install. The best HP badly installed will not heat your house as intended and/or will cost a fortune to run.
From reports on the Octopus Energy forum I gather that they use a very simplified cheap and cheerful install process (that’s cheap and cheerful to them, not necessarily the owner). However that is by no means unique to them.
I bought a Daikin (my other nearest match was Panasonic) partly because as an Octopus customer I hoped that their future smart tariffs might be able to control it and partly because they were top ASHP manufacturer in an Ethical Shopper Magazine review.
My home didn’t meet Octopus requirements (they are very fussy) and I went with a fairly local Daikin approved installer. I then had to learn how to change virtually every setting to get it working efficiently.
Incidentally, Octopus seem to be so fussy as they mass install to a particular process and they accept that it won’t produce passable results for all properties.
Beware of oversizing the HP. It is currently common practice to buy a gas boiler which is well oversize. This is because householders complain to the installer if the house/water aren’t warm enough but not when the gas bill is higher than expected. There are a lot of “installers” that have jumped onto the HP bandwagon in order to profit from a sellers’ market and the BUS grant. Make sure you buy from a company that have insurance backed guarantees.
My boiler had a potential output seven times that of my heat pump but we are still cosy all winter, have hot water on demand and lower electricity cost than we paid for gas.
Incidentally, the reason that people in your area are installing Vaillant could just be that they have an installer near you, that they are offering incentives to installers or that they have a huge marketing budget. That isn’t to say that you shouldn’t get one.
Tim
thanks so very much for all off this. I need to get of my bum and start getting quotes etc! Great to hear about hour success and lower bills too!
Lorrie
We’ve been considering a heat pump too, and agree with Tim that from what I have read and seen it is all about the quality of the installation. Although we haven’t yet taken the plunge I would suggest watching some of the Heat Geek videos for a fantastic introduction to the heat pump journey. Normally I wouldn’t recommend advice such as that from a less-than-independent source, but their introductory videos are pretty objective, (They also supply and install, which is why I say they are not a source of wholly independent advice.) They maintain a register of competent, independent installers who have trained on their courses. (I see they have a suggested £150 course for homeowners too). And they are one of the few companies whose competent installers offer (at around £800 extra cost, if I recall correctly) a guaranteed Coefficient of Performance, which could be worthwhile.
I don’t know the price but Heat Geeks will also do a thermal survey for you to use when looking for a pump/installer. This would also enable you to change radiators or do other work that might be suggested yourself or with a plumber that doesn’t charge crazy installer prices.
A proper thermal survey and heat loss calculation gives the best results but isn’t cheap. Most installers take 20-30 minutes to glance around the property (if you are lucky) and pluck a figure out of the air. Because the figure(s) reached are inaccurate they will also cover their backsides by saying that loads of radiators need upgrading. No one ever complains if a radiator is bigger than needed but they will if it’s too small. In fairness if the radiators are bigger than needed you can drop the flow temperature, get a better COP and lower the running costs, but you might need to live in the house a very long time to recoup the additional outlay.
I found this advice on the Heet Geeks website:
… although engineers say they have completed heat loss calculations, they very much vary on how in-depth they are.
If your surveyor has not measured every window, wall and door, as well as looked at the depth of the loft insulation, enquired about cavity insulation and measured every radiator, they have not performed a heat loss survey or calculation.
Just the details of the heat loss survey alone should take 1 to 2 hours on site to obtain, excluding time talking to the client about any options etc.
If you get to the installation stage and this information still hasn’t been taken, stop the installation and abandon the contract.
You need two sets of heat loss calculations, a whole house one for the size of heat pump and a room by room to determine what emitters (generally radiators) are needed. The two sets may legitimately not come to the same figure. As rooms can loose heat internally the total of rooms may exceed the total for the house.