Heat Geeks

john-306

matt_drummer said:

How is a buffer tank going to help?

A lot of Heat Geek trained installers like Vaillant heat pumps. These, and many others are designed to run at higher flow rates.

You won't get high enough flow rates through small pipes and it will be noisy.

At a flow temperature of 30c or less, even a small space requiring only 300W of heat will still need a large 3kW radiator and adequate flow of water.

Did Octopus install a buffer tank with your system? 
I said I didn't want one with my upcoming install but they insisted they had to be fitted, but were actually volumisers that they referred to as buffers. 
Could be telling me a load of rubbish just to shut me up.


I

Reed_Richards

I think the point of a buffer tank would be so that you could use a second circulation pump to try to get the water to the radiators through the small bore pipes fast enough.  Without a buffer between that circulation pump and the one inside the heat pump unit, the two might end up fighting each other.  I'm not competent to argue about whether you need two pumps here, but it's what the Urban Plumber uses in the video posted by @tacpot12 .  

Heat pump systems are typically set up to achieve a 5 C temperature drop across the radiators.  This requires a much higher flow rate than with a gas or oil boiler, which typically aim for a 10 to 20 C differential.  I presume the reason for seeking a 5 C temperature differential is so that you don't need even bigger radiators, because the heat output depends on the average radiator temperature.  But modern Low Temperature gas boilers try to use flow temperatures similar to those of a heat pump but do not, AFAIK, aim for a small temperature drop.  So perhaps there is a bit of a disconnect in heating philosophies there?

 Edit:  Talking about clashing philosophies, maybe the Heat Geek anti-buffer philosophy (which is not without merit) clashed with their small-bore-can-do philosophy and the former won?  So @thevilla got quoted for a larger bore but buffer-free system?   

matt_drummer

Yes, I have a volumiser. As far as I know, all Octopus Daikin installations are fitted with a volumiser.

A volumiser is not a buffer tank, there is no hydraulic separation going on. 

The volumiser is just a big piece of insulated pipe that is fitted to ensure that there is sufficient volume of warm water to carry defrosting of the heat pump.

They have no affect on efficiency and you are not heating more water than you need to. The amount of water heated is just the flow rate through the heat pump.

I could do with bigger pipes if I wanted to run a high flow rate.

I use huge radiators, a low flow rate and a large dT between flow and return.

matt_drummer

Reed_Richards said:

I think the point of a buffer tank would be so that you could use a second circulation pump to try to get the water to the radiators through the small bore pipes fast enough.  Without a buffer between that circulation pump and the one inside the heat pump unit, the two might end up fighting each other.  I'm not competent to argue about whether you need two pumps here, but it's what the Urban Plumber uses in the video posted by @tacpot12 .  

Heat pump systems are typically set up to achieve a 5 C temperature drop across the radiators.  This requires a much higher flow rate than with a gas or oil boiler, which typically aim for a 10 to 20 C differential.  I presume the reason for seeking a 5 C temperature differential is so that you don't need even bigger radiators, because the heat output depends on the average radiator temperature.  But modern Low Temperature gas boilers try to use flow temperatures similar to those of a heat pump but do not, AFAIK, aim for a small temperature drop.  So perhaps there is a bit of a disconnect in heating philosophies there?

 Edit:  Talking about clashing philosophies, maybe the Heat Geek anti-buffer philosophy (which is not without merit) clashed with their small-bore-can-do philosophy and the former won?  So @thevilla got quoted for a larger bore but buffer-free system?   

Yes, you can't put two pumps in series.

But a buffer tank won't give you two pumps assisting each other.

The water in the buffer tank is hydraulically separated with one pump on the heat pump side and the other on the house side.

You can therefore get different flow rates between both sides of the buffer tank.

I haven't watched the video but I assume that the idea is to put an even larger circulation pump on the house side of the buffer tank to deal with the small pipes?

I would expect it to be noisy.

Water takes the path of least resistance, plumbing some radiators in big pipe and others in micro bore will make balancing difficult I would think. 

matt_drummer

I watched the video.

He is very good, always is.

The circulation pump inside the heat pump was on it's limit and so a bigger one had to be fitted to get the required flow rate.

The big pump is feeding the radiators and the smaller pump inside the heat pump is just circulating water between the buffer tank and the heat pump.

In that house the flow rates are similar on both sides of the buffer tank so efficiency is not harmed too much.

Running two circulation pumps will affect efficiency, especially running flat out.

In that house the flow rate is 15 litres per minute and probably can't go any higher.

My heat pump runs at 6.5 litres per minute.

I have some plastic pipe and push fit fittings, and that is why I don't want to run high flow rates.

Reed_Richards

matt_drummer said:

Water takes the path of least resistance, plumbing some radiators in big pipe and others in micro bore will make balancing difficult I would think. 

I don't think you would be able to do balancing in the conventional way.  But I wonder if you could aim for a 5 C differential across those radiators with standard bore pipes and a 20 C differential across those with microbore pipes?  That means those radiators with the microbore pipes would need to be larger but that could be a better compromise than complete replumbing - if it is possible.

matt_drummer

Reed_Richards said:

matt_drummer said:

Water takes the path of least resistance, plumbing some radiators in big pipe and others in micro bore will make balancing difficult I would think. 

I don't think you would be able to do balancing in the conventional way.  But I wonder if you could aim for a 5 C differential across those radiators with standard bore pipes and a 20 C differential across those with microbore pipes?  That means those radiators with the microbore pipes would need to be larger but that could be a better compromise than complete replumbing - if it is possible.

At the flow temperatures a Heat Geek will be aiming for, I doubt you would ever see a dT of 20c across any radiator.

We haven't seen the OP's house so difficult to be sure about anything.

You would like to think that the Heat Geek trained installer came up with the best solution.

thevilla

Flow temp quoted was 45 degrees max.  Our boiler doesn't display temperature but we ran it pretty cool last winter. Never too hot to hold the radiators.

I think I'll give up on HG and try octopus.  Their fee is refundable.  I suspect they'll find the house unsuitable for their one size fits all approach but I'll give it a go.

After that I'll wait until our upstairs flooring needs replacing and try again - if I'm still alive 😄

john-306

matt_drummer said:

Yes, I have a volumiser. As far as I know, all Octopus Daikin installations are fitted with a volumiser.

A volumiser is not a buffer tank, there is no hydraulic separation going on. 

The volumiser is just a big piece of insulated pipe that is fitted to ensure that there is sufficient volume of warm water to carry defrosting of the heat pump.

They have no affect on efficiency and you are not heating more water than you need to. The amount of water heated is just the flow rate through the heat pump.

I could do with bigger pipes if I wanted to run a high flow rate.

I use huge radiators, a low flow rate and a large dT between flow and return.

Thank you. Good to know. 
On my house plan it shows location of "buffer".
This is my reply from Octopus...

At Octopus Energy, we install a Volumiser, which has one inlet and one outlet for connection to the heat pump and heating system, however, we do also refer to it as a buffer too. 

NedS

john-306 said:

matt_drummer said:

Yes, I have a volumiser. As far as I know, all Octopus Daikin installations are fitted with a volumiser.

A volumiser is not a buffer tank, there is no hydraulic separation going on. 

The volumiser is just a big piece of insulated pipe that is fitted to ensure that there is sufficient volume of warm water to carry defrosting of the heat pump.

They have no affect on efficiency and you are not heating more water than you need to. The amount of water heated is just the flow rate through the heat pump.

I could do with bigger pipes if I wanted to run a high flow rate.

I use huge radiators, a low flow rate and a large dT between flow and return.

Thank you. Good to know. 
On my house plan it shows location of "buffer".
This is my reply from Octopus...

At Octopus Energy, we install a Volumiser, which has one inlet and one outlet for connection to the heat pump and heating system, however, we do also refer to it as a buffer too. 

Most ASHP manufacturers insist on a minimum volume for their ASHPs.

Because it's not always easy for a plumber to calculate the minimum volume (although I don't know why), many/most will just insist on using a volumiser to ensure the minimum volume requirement is met (I have a 50L volumiser). This will ensure the defrost cycle can operate efficiently in winter.

The installer will not want phone calls from you at 5am on a cold winter morning telling them that your heating isn't working because the ASHP is frosted up all the time, and they equally will not want to have to argue with the ASHP manufacturer over any warranty work because they cannot guarantee that the system design has met the minimum volume requirements because the home owner has turned down half the radiators on their TRVs in unused rooms.

Most ASHPs also require a minimum flow rate and will throw an error if the flow rate drops below this.

My ASHP has a minimum volume of 50L, and a nominal flow rate of 34.6L/min. The minimum flow rate is 12L/min and I run at a constant flow rate of ~26L/min with 22/15mm copper pipework and two Wilo pumps.