BUS Grant requirements (conflicting info)

[JamesPa]

Explanations as requested:

 

Buffer tank is 50-200l tank between heat pump and emitter.  Flow and return from heat pump go to buffer tank, flow and return go from buffer tank to emitter (so 4 connections in total - hence 4 port).  It provides 'hydronic separation' (basically separating the system into two circuits).  Generally regarded (by those who have actually thought about it from a customer point of view) as a bad idea in 95% of domestic installations.  However all too frequently fitted or insisted upon by installers because it reduces the likelihood of certain types of call out (by masking the underlying problem).  3 port buffer tank is a variant with only 3 connections, possibly better than 4 port but still undesirable.  LLH (low loss header) is effectively a buffer tank reduced to a piece of pipe typically 1 m long, again with 4 connections. It performs essentially the same function.  Both of these require you to have a second water pump and, if not correctly set up/controlled, can incur an efficiency penalty of ~15%.  Avoid.

 

Heat exchanger also provides hydronic separation but the two lots of water dont meet, instead they exchange heat by passing both the water from/to the heat pump and the water from/to the emitters over a series of metal plates.  Nothing like as bad as a buffer tank, but still possible to mess up and again you need an extra water pump.  Avoid.

 

In addition to the efficiency penalty the above can cause, they also complicate diagnosis of certain type of fault.

 

I should stress that I am not an installer, plumber, or heat pump engineer, just an enthusiastic amateur who has been studying this stuff for more than 2 years.  On another internet forum the editor runs the occasional webcast.  One of the more recent ones was about buffer tanks, and he invited installers advocating for and against them to take part.  None of those advocating against accepted the invitation which made the webcast a bit one sided.  That says pretty much all you need to know unless you seek a detailed explanation of the pitfalls!

 

A volumiser is physically another tank but it has only 2 connections and is fitted either in the flow from the heat pump or the return to the heat pump.  No extra water pump is required as you haven't separated the system into two circuits.  Its sole function is to increase the volume of water in the system which helps with defrost and cycling (modes that heat pumps have to go through from time to time).  No real downside apart from the relatively small extra cost and space and may be necessary.  No reason to object if your installer wants to fit one.

 

I am aware that in posting this I risk getting a torrent of abuse from buffer tank advocates!

 

In case it got missed in what was a busy phase of this thread, can I just repeat what I and several others have said.  Neither a heat pump nor a boiler can supply two flow temperatures simultaneously so the way this illusion is achieved is by supplying at the higher flow temp and mixing down.  If you combine UFH and radiators this means that your heat pump needs to output at the higher temperature generally demanded by radiators.  This means that, unless you also design the rads to operate at a similarly low temp (very difficult) you lose one of the key advantages of UFH, namely it operates at a low flow temp where heat pumps are particularly efficient.  Avoid if you possibly can!

 

 

Edited Wednesday at 20:26 by JamesPa

[JohnMo]

To add to the above.

If you zone your property, that is have thermostats in many rooms with different time controls, asking for different rooms to be heated at different times, you will drive yourself into having a buffer. Why?

 

To protect the heat source, could equally apply to boiler or heat pump. Reason for this is to stop short cycling and give the heat source suitable circulation route. Plus for a heat pump suitable capacity to allow defrosting by providing a minimum required volume.

[Dillsue]

Does the BUS grant even apply to new builds?? Isn't it for replacing fossil fuelled heating.

[SBMS]

4 minutes ago, Dillsue said:

Does the BUS grant even apply to new builds?? Isn't it for replacing fossil fuelled heating.

Yes it does for self builders only. 

[HughF]

3 hours ago, Chanmenie said:

Not always, I had a Veismann Vitocal 151a installed, so that’s ASHP and internal unit with tank, buffer, pumps and all valve etc for £1800 

You can’t even buy a good heap pump cyclinder for that let alone the ASHP itself 

Exception rather than the rule….

 

[Beelbeebub]

3 hours ago, Chanmenie said:

Not always, I had a Veismann Vitocal 151a installed, so that’s ASHP and internal unit with tank, buffer, pumps and all valve etc for £1800 

You can’t even buy a good heap pump cyclinder for that let alone the ASHP itself 

That sounds like an extraordinary deal given those units retail north of £5k!

[Chanmenie]

8 minutes ago, HughF said:

Exception rather than the rule….

 

Yes probable but I designed the house to make the install really straightforward, the plumbers said it was the easiest ASHP they’d done and the shortest pipe runs.

[Chanmenie]

7 minutes ago, Beelbeebub said:

That sounds like an extraordinary deal given those units retail north of £5k!

They retail well north of 5k nearer or over 8k 

Fortunately the plumber charged me trade price on the unit but made £3k on the install which only took 4 days 

Edited Wednesday at 21:41 by Chanmenie

[ringi]

3 hours ago, Chanmenie said:

Not always, I had a Veismann Vitocal 151a installed, so that’s ASHP and internal unit with tank, buffer, pumps and all valve etc for £1800 

You can’t even buy a good heap pump cyclinder for that let alone the ASHP itself 

 

Who did the install?  What output is the Veismann Vitocal 151a?

 

What does the service cost to keep the warranty?

 

(That a very good price for one of the beat heatpumps.)

[Chanmenie]

5 minutes ago, ringi said:

 

Who did the install?  What output is the Veismann Vitocal 151a?

 

What does the service cost to keep the warranty?

 

(That a very good price for one of the beat heatpumps.)

A plumber local to me near Norwich

mines a 4KW but they go up to 16kw I believe 

 

no idea on service cost.

[G and J]

2 hours ago, Chanmenie said:

A plumber local to me near Norwich

mines a 4KW but they go up to 16kw I believe 

 

no idea on service cost.

Just had a quick Google on the Veismann Vitocal 151a.  Is it effectively a dual heat pump system?

[HughF]

No, it’s a monobloc with an integrated indoor unit/water tank. Fine if you want the schematic that’s included in the indoor unit, or want the convenience of a single box.

 

Not the way I’d go though….

[Chanmenie]

10 hours ago, G and J said:

Just had a quick Google on the Veismann Vitocal 151a.  Is it effectively a dual heat pump system?

No the indoor unit is the DHW cylinder and all the associated pumps and valves, makes it really quick and easy to fit, the outdoor unit is the heat pump 

[Chanmenie]

2 hours ago, HughF said:

No, it’s a monobloc with an integrated indoor unit/water tank. Fine if you want the schematic that’s included in the indoor unit, or want the convenience of a single box.

 

Not the way I’d go though….

Why not ? 
It’s very neat and efficient compared to having it all separately plumbed in.

Especially if you had limited space 

[HughF]

6 minutes ago, Chanmenie said:

Why not ? 
It’s very neat and efficient compared to having it all separately plumbed in.

Especially if you had limited space 

I prefer to design my systems from the ground up to not need half the crap most of these all-in-one hydro box/cylinders include - buffer, backup heater, extra zone valves etc.

 

I fitted all of mine into a cylinder cupboard that was 480mm wide. No extra pump, no buffer, just a 3 port diverter and that’s it.

 

Given the price disparity between gas and electricity we have here in the UK we have to design for maximum efficiency, unlike other European countries who can get away with less efficient designs.

Edited yesterday at 10:27 by HughF

[Chanmenie]

The Veismann unit doesn’t have any surplus crap.

the only valve is for Heating or DHW, the buffer is there to assist defrost, so no glycol or antifreeze valves needed.

 

I run mine open loop UFH so very simple.

 

I did my research before buying, I was going to buy and install myself, but for £1800 for a top end system with long warranty why would I do it myself ?

I think others get caught thinking they’ll save money doing self install and ignoring the bus grant.

Edited yesterday at 11:28 by Chanmenie

[sharpener]

1 hour ago, Chanmenie said:

the buffer is there to assist defrost, so no glycol or antifreeze valves needed.

 

Defrost cycle is a different beast from frost protection. You still need glycol or antifreeze valves for that unless you have a totally reliable electricity supply inc. some kind of backup against power cuts, even then you might be unlucky and have a compressor breakdown when you least want it.

 

IME it can get very cold in E Anglia when the wind is in the East, no shelter from hills anywhere nearer than the Urals.

[HughF]

5 hours ago, Chanmenie said:

The Veismann unit doesn’t have any surplus crap.

the only valve is for Heating or DHW, the buffer is there to assist defrost, so no glycol or antifreeze valves needed.

 

I run mine open loop UFH so very simple.

 

I did my research before buying, I was going to buy and install myself, but for £1800 for a top end system with long warranty why would I do it myself ?

I think others get caught thinking they’ll save money doing self install and ignoring the bus grant.

If it has a buffer, it'll have one more pump than needed. Both those are redundant in a properly designed system.

[Rudski]

22 hours ago, JamesPa said:

Buffer tank is 50-200l tank between heat pump and emitter.  Flow and return from heat pump go to buffer tank, flow and return go from buffer tank to emitter (so 4 connections in total - hence 4 port).  It provides 'hydronic separation' (basically separating the system into two circuits).  Generally regarded (by those who have actually thought about it from a customer point of view) as a bad idea in 95% of domestic installations.  However all too frequently fitted or insisted upon by installers because it reduces the likelihood of certain types of call out (by masking the underlying problem).  3 port buffer tank is a variant with only 3 connections, possibly better than 4 port but still undesirable.  LLH (low loss header) is effectively a buffer tank reduced to a piece of pipe typically 1 m long, again with 4 connections. It performs essentially the same function.  Both of these require you to have a second water pump and, if not correctly set up/controlled, can incur an efficiency penalty of ~15%.  Avoid.

 

So I have had time to read and look at what has been quoted to me so far,  the logic air tank system used by EDF has a built in low loss header tank and others quoted have the buffer tank installed, what system doesn't have the set ups you mentioned above?

 

Thanks for the explanation above.

[HughF]

23 minutes ago, Rudski said:

So I have had time to read and look at what has been quoted to me so far,  the logic air tank system used by EDF has a built in low loss header tank and others quoted have the buffer tank installed, what system doesn't have the set ups you mentioned above?

 

Thanks for the explanation above.

Any install by a heat geek or other competent installer... Buffer bad...

[Chanmenie]

3 hours ago, HughF said:

If it has a buffer, it'll have one more pump than needed. Both those are redundant in a properly designed system.

The buffer is only 16L it’s not your traditional extra volume buffer which I agree in a properly designed system with sufficient volume are not needed.

And it does not need an additional pump.

I think Veismann know what they doing 

[Chanmenie]

7 hours ago, sharpener said:

 

Defrost cycle is a different beast from frost protection. You still need glycol or antifreeze valves for that unless you have a totally reliable electricity supply inc. some kind of backup against power cuts, even then you might be unlucky and have a compressor breakdown when you least want it.

 

IME it can get very cold in E Anglia when the wind is in the East, no shelter from hills anywhere nearer than the Urals.

Well it’s installed exactly as Veismann recommend. With no Glycol or antifreeze valves 

[HughF]

41 minutes ago, Chanmenie said:

The buffer is only 16L it’s not your traditional extra volume buffer which I agree in a properly designed system with sufficient volume are not needed.

And it does not need an additional pump.

I think Veismann know what they doing 

I've done some more detailed research on this, including getting a look inside both the indoor and outdoor unit (via a YouTube training video)... Veismann don't do themselves any favours:

 

1. They call it a buffer - it's a 2 port volumiser purely for system volume for defrost. 16Ltrs seems a little small, but if that's what they want then that's fine by me.

2. They say the 'secondary circulation pump' lives in the indoor unit - the outdoor unit is without a pump so the pump in the indoor unit is the primary circulation pump.

 

Still seems unnecessary to put all that stuff in an expensive indoor unit that takes up more wall space. 90% of heat pumps have the expansion and primary pump inside the outdoor unit, with just a 3 port needed inside the house (or 2x 2 ports if that floats your boat).

 

I'm sure it's a fine unit, but it would need to be magically better than the usual stuff on the market to make me want to choose it.

Edited 22 hours ago by HughF

[Chanmenie]

7 minutes ago, HughF said:

I've done some more detailed research on this, including getting a look inside both the indoor and outdoor unit (via a YouTube training video)... Veismann don't do themselves any favours:

 

1. They call it a buffer - it's a 2 port volumiser purely for system volume for defrost. 16Ltrs seems a little small, but if that's what they want then that's fine by me.

2. They say the 'secondary circulation pump' lives in the indoor unit - the outdoor unit is without a pump so the pump in the indoor unit is the primary circulation pump.

 

Still seems unnecessary to put all that stuff in an expensive indoor unit that takes up more wall space. 90% of heat pumps have the expansion and primary pump inside the outdoor unit, with just a 3 port needed inside the house (or 2x 2 ports if that floats your boat).

 

I'm sure it's a fine unit, but it would need to be magically better than the usual stuff on the market to make me want to choose it.

Well for £1800 fully installed with extended warranty I’m not complaining.

You certainly could not purchase and install a better system yourself at that price,

[HughF]

Just now, Chanmenie said:

Well for £1800 fully installed with extended warranty I’m not complaining.

You certainly could not purchase and install a better system yourself at that price,

Yep, that's a bargain, given the retail price (which is unreasonable)...