Are ASHP the way to go?

matt_drummer

Reed_Richards said:

matt_drummer said:

QrizB said:

Reed_Richards said:

What is the white cylinder top right "...ukin"?  I thought it might be a buffer but it doesn't seem to have enough connections.

The brand is Daikin and I think the silver label says "volumiser"?

It is a World Heat volumiser with a Dakin sticker on it. made in Manchester!

If you have a volumiser you must also have a means of ensuring that there is flow, even in the scenario that your room thermostat calls for heat when the TRVs on all your radiators are closed.  If you have more than one heating zone that requirement must apply to every zone.  The usual central heating solution is to have an Automatic Bypass Valve; do you have one of those somewhere?  A lot of heat pump installations use a buffer tank instead of a volumiser.  The buffer removes the need for an automatic bypass valve but I don't know the reasons why a buffer might be preferred to a volumiser (any cost saving is minimal).  

I'm not a heating engineer so I may get this wrong but here is what I think/know.

I don't know if there is a bypass valve. I'm not sure it needs one.

My understanding of radiators is that they are not plumbed in series, they are plumbed in parallel.

If one radiator is shut off water still flows to all of the others. If that is the case it does not matter if they are all shut off.

The heat pump is no different to a gas or oil boiler, it's just a heat source.

A buffer tank is used where there are different flow rates between parts of the system. If my radiators couldn't flow enough water to satisfy the heat pump them you could use a buffer tank. I think it is called hydraulic separation.

A buffer tank makes the system less efficient. I understand many installers fit them to guarantee the system works whether it is needed or not. The buffer tank also ensures that you can get the correct delta t between the leaving and returning water temperature of the heat pump regardless of the delta t on the flow to and from the radiators.

The volumiser just adds volume to the system, nothing else as far as I am aware. It is inline on the return to the heat pump, it's just a well insulated piece of really large pipe.

So I think a buffer tank/tanks would be used where maybe you had radiators and under floor heating or maybe where you had micro bore pipes to the radiators. Basically when you need or have different flow rates around parts of the whole system.

I do not need and didn't want a buffer tank.


It's not the fullest explanation and if any of it is seriously wrong then I'm sure somebody will correct me.

I suggest watching some videos on heat pumps, particularly those from Heat Geeks.

DougMLancs

I’m glad Octopus aren’t fitting buffer tanks- a major cause of poor efficiency. You won’t see them on the continent but many installers here slap them in rather than design the system properly and educate the customer how not to treat it like a boiler.

JSHarris

Reed_Richards said:

matt_drummer said:

QrizB said:

Reed_Richards said:

What is the white cylinder top right "...ukin"?  I thought it might be a buffer but it doesn't seem to have enough connections.

The brand is Daikin and I think the silver label says "volumiser"?

It is a World Heat volumiser with a Dakin sticker on it. made in Manchester!

If you have a volumiser you must also have a means of ensuring that there is flow, even in the scenario that your room thermostat calls for heat when the TRVs on all your radiators are closed.  If you have more than one heating zone that requirement must apply to every zone.  The usual central heating solution is to have an Automatic Bypass Valve; do you have one of those somewhere?  A lot of heat pump installations use a buffer tank instead of a volumiser.  The buffer removes the need for an automatic bypass valve but I don't know the reasons why a buffer might be preferred to a volumiser (any cost saving is minimal).  

I started out with an auto bypass when I installed our ASHP.  It worked, but would sometimes throw a low flow fault.  This only happened at start up, when the UFH valves were all closed.  It was almost as if the auto bypass would sometimes stick closed, or just be a fraction too slow to open.  Not helped by the ASHP having a very sensitive low flow alarm threshold and the fault only coming up every week or two.

My fix was to remove the auto bypass and fit a low loss header instead.  The LLH completely fixed the problem.  Having no moving parts means the LLH short circuits the ASHP flow and return with very little resistance if it fires up before the UFH valves have opened.  Very impressed with the way the LLH performs, TBH, plus it isn't adjustable (I spent ages trying to adjust the auto bypass).

Reed_Richards

Radiators are indeed plumbed in parallel.  If all the radiators are shut off the water has nowhere to go so you would probably see an error condition and potentially the pump could be damaged.  A heat pump is no different to a gas or oil boiler and these should be installed with an Automatic Bypass Valve or something that performs the equivalent function (like a Low Loss Header or a Buffer).

Buffer tanks potentially reduce heat pump efficiency if they allow the flow and return water to mix.  If the water in the buffer remains stratified then there is no mixing and no loss of efficiency.  In either case a tank full of warm water must increase the heat loss from the system, compared to an insulated pipe.    

matt_drummer

Reed_Richards said:

Radiators are indeed plumbed in parallel.  If all the radiators are shut off the water has nowhere to go so you would probably see an error condition and potentially the pump could be damaged.  A heat pump is no different to a gas or oil boiler and these should be installed with an Automatic Bypass Valve or something that performs the equivalent function (like a Low Loss Header or a Buffer).

Buffer tanks potentially reduce heat pump efficiency if they allow the flow and return water to mix.  If the water in the buffer remains stratified then there is no mixing and no loss of efficiency.  In either case a tank full of warm water must increase the heat loss from the system, compared to an insulated pipe.    

I guess it must have a bypass valve of some kind then as I don't have a low loss header or a buffer tank..

This volumiser is just a large insulated pipe, it wont lose heat any more than the rest of the insulated pipework. As far as I am aware, the water doesn't sit in the volumiser when the pump is running, the water flows through it, it's not a tank for holding water

Everything I have ever heard about buffer tanks is that they reduce efficiency. Whether that is true or not does not really matter to me, I am pleased that I don't have one.

If the flow to and from the heat source remains separated in the buffer tank from the flow and return to the emitters, where do the emitters get their heat from? There must be a transfer of energy from one side to the other? That is where I thought the inefficiency came from?

All that I have read and watched suggests that buffer tanks and low loss headers are installed to compensate for poor design or design limitations where one or more parts of a heating system require different flow rates and delta t's to other parts.

My simple theory is that if you can go straight from the heat source, around the emitters and back to the heat source at the correct flow rate and delta t, then that is the simplest design and the most efficient. It means that the heat source and the emitters are perfectly matched and don't require any meddling with to work together in perfect harmony.



Anyway, I'm not sure what any of this has to do with your original question about my install.

Have you seen something that makes you suspect that it hasn't been installed correctly?

matt_drummer

Reed_Richards said:

Radiators are indeed plumbed in parallel.  If all the radiators are shut off the water has nowhere to go so you would probably see an error condition and potentially the pump could be damaged.  A heat pump is no different to a gas or oil boiler and these should be installed with an Automatic Bypass Valve or something that performs the equivalent function (like a Low Loss Header or a Buffer).

Buffer tanks potentially reduce heat pump efficiency if they allow the flow and return water to mix.  If the water in the buffer remains stratified then there is no mixing and no loss of efficiency.  In either case a tank full of warm water must increase the heat loss from the system, compared to an insulated pipe.    

I think what you are talking about is an ESBE valve.

These are normally fitted with an ASHP, all the people that came to see me about a heat pump spoke of this.

I heard the installers talking about the fact that this heat pump does not require one but I either didn't hear why or don't recall why.

So now thinking about it, I don't think I do have an automatic bypass valve in the airing cupboard as I think that is what the ESBE valve does and I don't have or need one.

Octopus will come back in a couple of weeks to check the system in a couple of weeks so I will try to remember to ask about this and I will let you know.

My installation is under guarantee for five years and the heat pump for seven years. If there is an issue I dare say it will become apparent with this time frame.

Reed_Richards

I have an ESBE valve but it's a thermostatic mixing valve on the output from my hot water cylinder.  This serves two purposes.  It allows me to store water at a hotter temperature than I want to use it at.  Normally the storage temperature is 50 C but under certain circumstances it can be as high as 75 C.  If I store water at a higher temperature it means I get more water at the temperature I actually want, which is probably about 45 C.  It also keeps my other half happy as she does not like hot taps that dispense water that is too hot to touch.

In my old house I had a gas boiler but also stored the hot water at 50 C.  Every Sunday morning the boiler would perform a Legionella cycle and take the cylinder temperature up to 60 C.  This was noticeable but never caused any problems, presumably because when you turn on the tap the water initially heats up the pipe run so what comes out is not instantaneously at 60 C.     

matt_drummer

Reed_Richards said:

I have an ESBE valve but it's a thermostatic mixing valve on the output from my hot water cylinder.  This serves two purposes.  It allows me to store water at a hotter temperature than I want to use it at.  Normally the storage temperature is 50 C but under certain circumstances it can be as high as 75 C.  If I store water at a higher temperature it means I get more water at the temperature I actually want, which is probably about 45 C.  It also keep my other half happy as she does not like hot taps that dispense water that is too hot to touch.

In my old house I had a gas boiler but also stored the hot water at 50 C.  Every Sunday morning the boiler would perform a Legionella cycle and take the cylinder temperature up to 60 C.  This was noticeable but never caused any problems, presumably because when you turn on the tap the water initially heats up the pipe run so what comes out is not instantaneously at 60 C.     

It sounds right about the ESBE valve, I don't think it has anything to do with bypassing.

I have never installed a heating system from scratch, only worked on them a little.

With regard to a bypass valve, as the radiators are obviously in parallel, if they were all closed, wouldn't the water just flow around the pipes that feed the radiators, not go through any radiators and make its way back to the heat source having lost very little temperature?

Reed_Richards

matt_drummer said:

With regard to a bypass valve, as the radiators are obviously in parallel, if they were all closed, wouldn't the water just flow around the pipes that feed the radiators, not go through any radiators and make its way back to the heat source having lost very little temperature?

You're assuming that there is something at the end of the pipe run that connects the flow pipe to the return pipe without passing through a radiator.  There isn't.  If there was it would tend to short circuit the radiators.  

matt_drummer

Reed_Richards said:

matt_drummer said:

With regard to a bypass valve, as the radiators are obviously in parallel, if they were all closed, wouldn't the water just flow around the pipes that feed the radiators, not go through any radiators and make its way back to the heat source having lost very little temperature?

You're assuming that there is something at the end of the pipe run that connects the flow pipe to the return pipe without passing through a radiator.  There isn't.  If there was it would tend to short circuit the radiators.  

I was assuming that.

I need to go and look at a plan of heating pipework so I can get in my head how the water gets back to the heat source.

Thanks.