Posted by: @riponowl

I'm having a Samsung 12kw monobloc heat pump installed today. The fitter gets part way through the install then tells me there isn't space for the buffer tank. He says he's checked with the office and my 7 rad system doesn't actually need one.

This doesn't sound right to me but without the technical knowledge I can't be sure.  Does anyone on here know if this is true?

Hi,

Look through the manual for your particular model of ASHP to find the minimum system water capacity requirement. Look at the specification for each of your 7 radiators and find the water volume of each. Add up the total volume of the 7 radiators and add maybe 10% to 20% for the volume of the pipework.

If the water volume of the radiators and pipework are greater than that specified by the ASHP manufacturer then it should be acceptable to operate without a buffer tank provide you don't have TRV's installed except in the bedrooms.

If you are still in doubt then ask the installer to explain in detail how, a buffer tank was initially specified, but is now no longer required.

@derek-m Thank you for responding. All the rads are specified to have TRVs on them (the install isn't finished yet). In fact I'd like to update them to smart TRVs eventually so I can schedule them for different times of the day.

Posted by: @riponowl

@derek-m Thank you for responding. All the rads are specified to have TRVs on them (the install isn't finished yet). In fact I'd like to update them to smart TRVs eventually so I can schedule them for different times of the day.

Hi,

Did you specify TRV's or your installer? Are you also having thermostats?

@riponowl, this may help: https://renewableheatinghub.co.uk/why-do-you-have-a-buffer-vessel-with-a-heat-pump

@derek-m A single Hive controller is being installed. My existing rads just had manual turn valves which never turned. I had to chase up the supplier after they sent the quote to make sure they would all the new ones would have TRVs so that they would be easy to replace with smart TRVs if I wanted to do that at a later date. 

The most telling factor is that the installers turned up with a buffer tank, cut out a section of the vinyl flooring on which to fit it only to decide later that there wasn't space. It was only when I queried if they were putting in a buffer that installer came clean on what had happened. It was clearly part of the spec.

I'm going to get an update from them shortly, I'll report back in a bit.

@editor Thank you, that is really interesting. I almost feel bad for giving the installer a hard time now (almost).  It seems to be at odds with this though

https://www.kensaheatpumps.com/buff-up-your-knowledge-of-buffer-tanks/  

Now I really am confused.

@riponowl, I have to be honest, the buffer tank is a point of contention. We have one, and the industry seems to be split. Some installers insist on having them, others say that they are there to bail out poorly designed and installed systems. From what I've read, and I'm not an expert, having a well-designed system with no buffer tank and no TRVs on rads leads to much better efficiencies.  

We have a buffer tank like I've said, and we have TRVs, and we have a SCOP of 2.7-2.8 which is quite reasonable and which we're not dissatisfied by. 

Well, the install went ahead without the buffer, there was absolutely no space near the tank so I will so how it goes. I will have a better idea about how it is performing in a week or so. I have more pressing problems with non performing rads to deal with first 🙁

Thanks again to all contributors.

Posted by: @riponowl

@derek-m A single Hive controller is being installed. My existing rads just had manual turn valves which never turned. I had to chase up the supplier after they sent the quote to make sure they would all the new ones would have TRVs so that they would be easy to replace with smart TRVs if I wanted to do that at a later date. 

The most telling factor is that the installers turned up with a buffer tank, cut out a section of the vinyl flooring on which to fit it only to decide later that there wasn't space. It was only when I queried if they were putting in a buffer that installer came clean on what had happened. It was clearly part of the spec.

I'm going to get an update from them shortly, I'll report back in a bit.

Hi,

TRV's and thermostats were developed for use with gas and oil boilers, whose water flow temperature was much higher than that required to heat the home. An ASHP can control the water flow temperature down to much lower levels, in fact the lower the temperature, the more efficient the system will operate.

Of course it is your choice if you wish to have TRV's and thermostats installed in preference to the control system specifically designed for the ASHP.

@derek-m Thanks!

I just wanted to be a little more energy efficient by having the upstairs rads turn down during the day and the downstairs rads turn down a little at night. It's no deal breaker though, right now I will be happy if it just works.

@riponowl 

It's unlikely to save you much if any money but you might want the option of TRVs in the bedrooms for comfort (if you like a cooler room).  That's what I've done but they are fully open most of the time.

So I finally have the MMSP up and running and have some data from PassivLiving. Overall efficiency is at 3.65 which I am assuming is good for this time of year?

This is the graph from the last few days. The purple line at the bottom which is the heat output clearly shows the heat pump coming on and going off a fair bit but imagine that's more to do with the thermostat reaching temperature and switching the heat pump off. I'd been under the impression that it would just run constantly but it is actiing more like a gas boiler.

Anyway here is the graph, any observations gladly received.

@riponowl 

I think that's what's happening.  You can see the flow temperature dropping and rising in sync with the bursts of power.  That is likely to be due to your thermostat switching the ASHP on and off.  I don't think it's the ASHP cycling as the flow temp is dropping too much and the time period is too long.  It looks like you are running weather compensation as the flow temp seems to vary with outside temp.   

You could try turning your thermostats up a few degrees; your house will probably get hotter but the ASHP will run more steadily.  You can then adjust down the flow temperature if you need to, which will lower the house temperature. 

Your COP looks OK but could maybe be improved.

What's the trace at the very bottom? 

@kev-m Yes, weather comp is set to 37-45. Thermostat up and flow temp down might work (and keep the wife happy). I don't what the trace at the bottom is, maybe someone on here can tell me.

Thanks for your help.