Are Buffer Tanks Required For Air Source Heat Pump Systems?

[@timnewton7422]

Excellent discussion… so glad I removed our buffer tank. We needed to learn about energy carrying capacity of a few short runs of microbore within the existing few rads but everything now runs effectively down to 35c LWT using one circ. pump. Installer agreed to make changes FOC. (4 bed house, 8.5 ecodan, 15 rads twin coil 250L unvented tank.) cop 3.8 to 4.2 but possibly up to 18% underestimated efficiency as MELCloud sourced info. Perhaps manufacturers need to review and improve their own brand performance reporting as they are probably inadvertently damaging their own brand!

[@steveholliday1599]

I enjoyed this discussion. I have two installers quoting, one proposing a buffer, the other not. I will be challenging each on their respective reasoning when they each re-visit next week. However, I think perhaps the most important point (only touched on on the video) is that for 90% of all UK houses the space requirement is critical. I am replacing a combi boiler and will be installing UFH downstairs and rads upstairs and brand-new piping throughout, plus removing and reinstalling CWI, massively upgrading the loft insulation and installing high efficiency windows and doors. But - the one thing I cannot easily do is find space for the required 'plant room'. This is the most challenging issue. As a consumer I see pictures of amazing and beautifully designed plant rooms, full of tanks, and expansion vessels and lovely parallel runs of copper pipe. I appreciate the engineering in it, but where the heck am I going to put all that? I have a 4-bed detached house, but whilst not the smallest property in the world, it is very 'compact' and there just isn't any sensible location for this stuff . So - losing the buffer tank would be incredibly helpful, even if it somehow made the efficiency worse (which it doesn't appear to do from this discussion). I am also contemplating a Sunamp unit to save space of the HW cylinder.

[@sygad1]

Thoroughly enjoyed this, thanks for the informative discussion

[@RenewableHeatingHub]

Thank you. Glad you found it interesting.

[@ryanwjk]

Hydronic design expert here. I've enjoyed the discussion, but it seems there are quite a few solutions that haven't been considered-like 2-port buffers (not volumisers), for instance. However, rather than focusing on that, I sense there's a lack of clarity about the primary goals of any heat pump installation. Is the aim efficiency (and if so, is it efficiency over the heating season or throughout the year)? Is it comfort and control? Or is it reliability across the lifespan of the unit? The answer, of course, is that it's all of these. But the challenge with retrofitting heat pumps is that these objectives aren't always aligned. For example, achieving high efficiency doesn’t necessarily guarantee good control-after all, the most efficient heat pump is one that’s turned off. I appreciate the open exchange of knowledge, but let’s make sure we’re not missing the forest for the trees.

[@atvarsgr]

I have 226m2 house , all heated floors (ground floor 12 loops, first floor (bedrooms) 11 loops), have Bosch Compress 7000iaw 13kW heatpump coupled with 500l buffer tank and 300l hot water tank. Heat pump is programmed to heats up buffer tank from +26 to +37C range, that 5.5kWh of energy is suffiecient for about 5 hours. Heat pump runs for 1h15min cycle to heat up buffer tank, then 5 hours off. On house side from buffer tank I have 2 Bosch pump groups, one for each floor. Average COP is 4.6, in fact without buffer tank it would be impossible to undestand your house energy consumption and double check your heat pump's COP. In one cycle heat pump consumes 1.45kWh of electricity and produces 6.8kWh of heat energy (11C * 500l * 1W = 5.5kWh) + 1.3kWh house consumes (5.5/5 * 1.25) during the 1h15min cycle heat pump is running. Heat pump computer shows the same COP. I am ultra pleased with my system.

[@Bushtuckerman71]

I can store energy in the accumulation tank when the kwh price is cheaper or when there is a lot of solar energy. The thing is that you need a shunt motor valve to regulate your heating curve. And a regulator connected to octopus say to the heatpump when to produce heat.

[@redshift3]

Love the point that efficient heat pumps protect grids from requiring reinforcement. This point needs to get to DESNZ, ENA, DNOs and NESO

[@typxxilps]

Looks like the UK is a complete different market. Here in Germany all the plumbers and HVAC guys are adding saftey margins onto each other to achieve 1 goal: the customer can never complain that it gets to cold, no matter what cause then he will not be sued Safety margins piling up and heatpumps 2 times too big. The customer pays at the end what he is asking and far before the customer can realise what he has gotten. And close to no hvac engineer or plumber or what soever is willing to listen and to build a heatpump without a buffer. Impossible. The closest you can get is to convince to use a 50 L tank for defreezing in the return flow - and 2 put in 3 ways walves to proof who is right which means the customer can use the highway and check if it works in his mostly older house from 60s to 90s or if he has to take the detour via buffer. Only scientists, researchers and profs are warning: do not pile up saffety margins on safety margin cause you will get a far too big heatpump which can modula, but only in a certain range which is determined by the max heating power / output. 12 kW can modulate down to 4,4 kW while the 8 kW can run below 3,5 kW . Looks like no difference but that is a difference of 3°C when the cycling would start. 4°C or 7°C makes here a difference of 1200 heating hours where the bigger one is turning on and off while the other is running fine. But it is hard to find one to build it. And heatpump installation price here is usually 25000 - 30000€ or about 22500 GBP to 27000 GBP cause heatpump prices from Viessman and Vaillant and all others are double of what they cost in the UK which has even a higher VAT. That is caused by the stupid grant program where the manufacturer, the designer, the plumber and everyone else wants his bonus from the grants the customer gets at the end. Tell the plumber you would get a 65% grant while the usual is 35% your price will explode that at the end you pay just a bit less thatn the guy with low subsidies. Price is based on the grants you get and all are participating in the plundering tour cause lobbyism has worked its way into law and everyone gets his share on the long way till the customer will have gotten the grants. We decided to do it our own and bought a heatpump listed in germany as qualified for grants (part of the BAFA list) which is made and china and sold by many on their own german label. 1800€ was the 8 or 12 kW price - nearly the same, only difference were 10€ . We decided to go for the smaller. We still have an oil condense heater and can live with that cause we are going to heat in a monovalent way where below -3°C the heatpump will rest and the oil heater will run. But the most funny part here was to watch 4 british sceptical about any kind of buffer tank where here a buffertank is the first point to discuss, but only how big it can get like 1000 Liter, the bigger the better (for the profits). No one will question that. Except engineers and Profs who are warning day in and day out the home owners to check their heating load carefully and optimize first to avoid a too big heatpump. Too small can be fixed with a split AC used for heating easily. Too big can not be fixed. Hats off, great round table and conversation.

[@MrFlyby34]

Prices for install in Germany are bonkers. Most probably over engineered as well. I had a look at some heat geek elite installers here in Britain recently and the initial quote I got online was way higher than other installers. Maybe I am wrong about this but isn’t heat geek a bit overpriced?

[@anthonywebber7434]

HI guys great content, very useful I am in the buying process at the moment. Do I need a buffer tank if I have a cascade system 2 x 10 KWh . Also I have a large house 300 Square meters. If a 18 KWh AHP could work would this be better than 2 x or 9 KWH..

[@RenewableHeatingHub]

According to Simon: “The client does not need a buffer for this system. We are actually installing a similar system on open loop, 2 10kw Vaillants. Our design is to size a distribution header on the flow and return. in our case this is 76mm pipe with both heat pumps flow plumbed into the same pipe and the same with the return. That pipe then changes to 35mm at the house which is what’s needed to meet the pressure drop and transport 20kw of energy around the system. It’s all open loop. Very unlikely to find an 18kw heat pump that actually doesn 18kw at dot say -3 with any flow temp….even 35 degrees. I think Clivet do one but that’s about it. It won’t be a patch on the efficiency of a well designed vaillant cascade.”

[@kbunboxing938]

@@RenewableHeatingHubI need to see a video on this install, done quite a few cascade vaillant but always used the hex module this seems like an interesting approach.

[@gerardfry4876]

@@RenewableHeatingHub do you have an example picture or schematic of this for visualization? im struggling to see how this would be piped up?

[@RenewableHeatingHub]

Sure. Please visit this forum post. Posted some diagrams for you: renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/avoid-the-heat-pump-villain-why-low-loss-headers-and-buffers-can-sabotage-your-heat-pumps-efficiency/paged/13#post-38671

[@nervousfrog101]

Thanks for explaining the difference between a buffer and a volumiser I'm not sure if I have never had this explained before or not. Maybe just with all the info that gets thrown at you as a heat pump owner maybe I just never understood. Some thing I'm still not quite sure about though is can a volumiser have a negative impact on efficiency with a radiator only system no under floor if so can it be significant?

[@AdamShort-tf1vg]

I am no expert but a volumiser doesn't have to be huge, maybe 25 litres on the return flow back to the heat pump. Think of it as the first warm water source to go back to the heat pump. This water is used on defrost cycles so it doesn't draw warm water in your radiators to defrost. When the defrost cycle is over and the heat pump starts to heat again, the heating water only needs to heated up by smaller margin and this can help prevent the endless de-frost cycling they were talking about.

[@stevencampbell6359]

Can I ask the definition of "open loop"? Does that mean emitters just have fully open pipework and lock shields are all wide open, or is flow restricted for balancing purposes? I assume there must be balancing of the emmiters or parts of the system farthest from the heat source wont get warm. Or is design that areas wanting warmer temperatures should be first in the routing of an open loop system?

[@AdamShort-tf1vg]

There are so many studies available via google which explains the impact buffers can have on efficiency. Many installers STILL won't fit a system without a buffer tank. You do have to be very careful to research and choose a qualified, competent and knowledgeable installer / company. If they can't explain why it has to be a buffer tank and not a volumizing tank then find someone else!

[@71brp84]

Sure, in new systems, there's no excuse for using any unnecessary components but, buffers shouldn't become extinct. There are always going to be outlying cases in retrofits where it's possibly the only realistic option. I thought Simon was going to touch on this at one point, when he started talking about and pressure loss. How would he deal with microbore embedded in walls when the pressure drop of the index circuit it too great for the ASHP's internal pump? There are plenty of 70's and 80's properties where re-piping the whole place is just not a realistic option. Even more recent properties with plastic microbore. What if the customer doesn't want their property ripped apart because "it will be more efficient". Spend a bit extra each year on your heating bill, or spend thousands extra getting half the property re-piped and redecorated.

[@ReneArtoisMr]

I never heard why a (correctly installed parallel buffer, preferably connected using two pipes) would harm efficiency? Furthermore it’s easier said than done to repipe your home for optimal efficiency. For me it’s out of the question. Using the wrong manifold units for underfloor heating will cause an increase in CV temperature, connecting your buffer the wrong way will increase CV temperature, both together can lead to an over temperature from 15-20 grc causing a huge impact on heatpump efficiency. Using a buffer the right way, decreases the amount of compressor starts, makes defrosts easier and assures that zone temperature control doesn’t frustrate your heatpump.

[@robveck6683]

Homely (an AI system to manage the heat pump) doesn’t work with a buffer tank. It needs the flow and return temperatures to accurately determine the efficiency of the system and the buffer tank disrupts its algorithms. Once we got written confirmation from Homely, and agreement from Midea that removing the buffer tank wouldn’t affect the warranty, the installer removed the buffer tank . COP then improved.

[@Burtis89]

This is interesting I was considering I have a buffer 😕 so maybe a waste of time then. My circulation pump in the loft is loud and set to full speed. The Midea app and controller is pants 😅 The info on it is awful and probably inaccurate. My installer doesn't want anything to do with the noise produced... And will charge me to remove the buffer to try open loop...

[@chrismorrish130]

@@Burtis89 If you've got a buffer the secondary pump ought to adjust the flow rate to match the delta t of the heat pump. A fixed speed pump won't do this. Otherwise the heat pump will have a higher flow temperature than necessary, reducing COP.

[@heatpump8566]

A great scop on an open loop system is great for the vain plumbers. My hp is switched on and off to make me comfortable. It costs a lot less to run than leaving it on all the time. BUT my scop is a bit less Scop is a vanity project

[@RenewableHeatingHub]

renewableheatinghub.co.uk/heat-pump-scop-arms-race

[@norfolkngood8960]

Ultimately run it according to your means and comfort that's all that counts at the end of the day. In winter we have ours on all day on the stat and that's by far cheaper than setting schedules. We do have a schedule set for a higher temp overnight downstairs with the much cheaper rate to warm the house up for the following day

[@cvarsani2190]

I think you should have invited HeatGeeks or UrbanPlumbers 👍

[@RenewableHeatingHub]

We have extended invites to a lot of installers. We're going to have Heat Geek on future videos.

[@garrywhiting8398]

James Clarke is a "Heat Geek Elite" and has featured in at least one Heat Geek channel video...

[@RenewableHeatingHub]

Good point. Simon Murray is also a Heat Geek. I assumed Chandre meant some from Heat Geek like Adam.

[@evilspoons]

Production critique: please ask the folks with laptops to stop banging the table the laptop is sitting on. Their jiggling cameras are giving me a headache. The guy in the top left and top right keep doing it and it's not great.

[@RenewableHeatingHub]

😂 This was our launch episode and we learned a lot from a production perspective, from jiggling cameras, to audio feedback to lighting. We're recording our next video next week, and have a long list of dos and don'ts

[@mackay250]

So are Octopus right to put a volumiser on the return? Is that a buffer tank in disguise?

[@RenewableHeatingHub]

Volumisers are not buffers, so not really a disguise. But if they say they’re putting in a volumiser, and the plumb it like a buffer, then it’s definitely an issue. Do you have more specifics?

[@mackay250]

@ Not really, octopus said they have to fit a volumiser on t.he return and I was a bit worried about efficency after watching this video. Hopefully it should be OK?

[@RenewableHeatingHub]

Volumisers are fine. They add volume to the system and can be helpful. Volumisers won’t adversely affect the system.

[@jamesblofthouse5542]

Wow, so dangerous, yes heat pumps are inverter driven and hence output is variable, radiator/emmitor demand is variable, the two however are rarely equal, this is why you're promoting an "open loop". No discussion on compressor wear when buffer vessels are not installed. If you want a heating system you can control and one you can rely on use a buffer, use zone control on your heating. Decoupling your heat pump fro. Your home is one of the most critical aspects, what is being promoted here is saving cost on a buffer and piping to enable volume install.

[@chrismorrish130]

A good install has the emitters sized as large as possible to meet the design heat loss at as low a flow temperature as possible. The heat pump controller then uses weather compensation to match the heating load required. It takes the outside temperature and sets the flow temperature to enable the emitters to match the heat loss. So the heat pump output will often meet the emitter load. When it won't is on milder days when the emitter requirement is below the minimum output of the heat pump. The heat pump then has to cycle on and off to average the required flow temperature. With a zoned system and any zones turned off, this cycling will be more frequent. Without zones, and a larger system volume the cycling will be less frequent. The system volume should be large anyway as we need large emitters / UFH for an efficient system anyway. A buffer can make the cycling less frequent but unless the emitter side pump can target the DT of the heat source DT then efficiency will reduced significantly. This is what Heat Geek teaches.

[@hvacdesignsolutions]

Most installers won't omit a Buffer from their system......what then?

[@RenewableHeatingHub]

That's the million dollar question.

[@AdamShort-tf1vg]

You can find a Heat Geek and they will not recommend a buffer unless they think it's vital for your specific circumstances.

[@Rowlysrenewableroadshow]

This video had the potential to spark a great debate on heat pump system design. Unfortunately it was the equivalent of Question Time with a panel of MP’s from the same party…… Maybe next time do it with Brendon and Ken Bone, Paul Spence, a manufacturer and maybe a Heat geek…….now that would make for a much more diverse conversation. 🤣

[@RenewableHeatingHub]

Thanks for the feedback. As mentioned during the video, I invited over a dozen installers that I know are pro buffer tank to have that diversity in the conversation. They declined to come on. But I take your point. This was a test run, and we have Heat Geek and manufacturers lined up for other videos.

[@darrenadams2640]

@@RenewableHeatingHub Now that will be valuable - when is it likely to happen?

[@RenewableHeatingHub]

It's taking shape. It's a matter of scheduling. These are all busy guys with schedules that don't align a lot of the time. They're all on board to do it, and we're aiming to get it done in mid to end October if all goes well.

[@paulcornock8287]

A very bias panel of people in this discussion that seam to single out certain business yet there are hundreds of company's large and small that are installing buffers for one reason or another, yet you assume they are bad installs! has any one you reached out to these bigger company's to find out why they are using the installation type they are ? as for this constant comparison of SCOP's there are hundreds of reasons why a SCOP could be low. Poor insulation, old windows etc and not always due to buffers. All these types of discussions are causing is more customer uncertainty. Why not show some positivity to what some of these company's are doing like enabling customers with any financial backing the chance to have a heat pump. lower tariffs and helping turn the industry from gas to renewables.

[@RenewableHeatingHub]

We invited over a dozen installers that fit buffers to have an objectives conversation. They all declined. I can’t force people into the show. But we will revisit this in a few months time.

[@paulcornock8287]

@@RenewableHeatingHub Do you blame them i would have to ask " who the hell are you" bar a few designers/installers that have an opinion. you should never have made a podcast without getting the facts first!

[@RenewableHeatingHub]

Can you please specify what you found factually inaccurate?

[@norfolkngood8960]

In any of those circumstances you shouldn't be fitting a heatpump tho. First thing you fix is all of that stuff fitting a heatpump with poor insulation, old windows etc is just asking for trouble.

[@norfolkngood8960]

​@@paulcornock8287who the hell do you think you are shouting from the cheap seats? It's really easy to sit behind a keyboard and moan about something harder to join the conversation and constructively put your point across without sounding like a butt hurt installer who has taken everything as a personal attack.