Do I need a buffer tank

[James94]

Hi all, first fix plumbing is underway and I’m confused on wether I need a buffer tank or not. So I’m hoping someone with more knowledge than my plumber/“heating engineer” can advise me.

I’m having underfloor heating downstairs and in two bathrooms upstairs using the clippa plate system from wunda. These will run off 2 separate manifolds with an estimated total volume of water of 134.36 litres and a heating demand of 10.7kw according to wundas calculations. Obviously the demand to heat the two bathrooms will be a very small part of that 10.7kw.

I have an Ideal Vogue S32 GEN2 system with a modulation rate of 7:1 so 4.57kw if I’m correct.With a 300litre uvc. 

Do you need any more info to be able to decide if I need a buffer or not? Sorry to sound thick but i was hoping my plumber would be able to take care of this as I don’t have a clue when it comes to this sort of thing.

 

James

[joe90]

Well I was advised to have a buffer tank and others here have not installed one, one advantage of a buffer tank is having an immersion but this could be replaced with a Willis heater if no tank is installed. Others will be along shortly with their views!

[JohnMo]

4kW requires around 120L system capacity.  The capacity is the bits of the system that are active.  So if everything was off except one bathroom you may need a 70 to 80L.

 

So you need to couple together large proportion of the heating as a single zone.  If you run as a single zone no buffer needed.

[James94]

@JohnMo not sure how id go about coupling the heating zones together to achieve a single zone. ive got a 12 port manifold for downstairs UFH with 5 zones, 2 port manifold upstairs with 2 zones, 5 radiators with smart trv's.

would i be better of buying a buffer tank or could i make this work as a single zone?

[joe90]

Having a buffer won’t give you a single zone. I only have one zone simply by controlling the water temp to that whole manifold and no actual loop controllers (apart from balancers for those loops).

[JohnMo]

I would be inclined to make the whole downstairs a single zone, use a single thermostat centrally located.  I have one in the hall. Kitchen/diner, lounge, bathroom are all served by this thermostat.

 

En-suites have no thermostat the come on whenever there is a call for heat from the main living space or bedrooms.

 

My bedrooms each have there own thermostat, but very often set so low they are off.  But I am thinking to make them a single zone also, because if one room needs heating they all do in reality.

 

Or as Joe ditch all the thermostats.  If you go on to the heat geek website it goes in to detail of how to balance the system.

[James94]

@JohnMoWell almost a year has passed and our moving in date will soon be approaching, not sure if our “gas engineer” fully understands the concept of buffer tanks and short cycling. He’s first fixed without a buffer tank and I’m hoping it won’t be too much work now to integrate one.

 

Id like the option to be able to control individual zones on downstairs UFH, I’ve already noticed some of the north facing rooms are noticeably cooler. 

 

Here’s a photo showing what we currently have. How difficult will it be to add a buffer to this system? to stop short cycling and maybe increase efficiency.

 

I will speak with our plumber once I have an idea of what is required.

 

James

 

Edited April 18, 2023 by James94

[Iceverge]

11 minutes ago, James94 said:

like the option to be able to control individual zones on downstairs UFH, I’ve already noticed some of the north facing rooms are noticeably cooler

 

Probably best to let the house settle into use before making any decisions. 

 

If you run a lower flow temp for longer periods rather than hot and short then the colder rooms should equalise as the hotter rooms will draw almost no energy due to the smaller delta T. 

 

[JohnMo]

As @Iceverge says let the house settle, would try it without a buffer for now, has he plumbed to allow your boiler to run weather compensation?

 

if you add a buffer I would install as a two port configuration in the return line coming from the UFH. So in the pipe between the outlet of the UFH going back to the boiler. That would be easiest and most efficient.

 

Would get him to do the pipe insulation properly it's a mess.  Every gap is an energy loss.  All the changes of angles should be mitred. Assume the photo is in the loft?

[James94]

@Iceverge @JohnMo, thanks for the advice.

 

just worried that with a 2 port manifold for upstairs bathrooms and rads for 4 bedrooms it will short cycle/ be inefficient and cost a fortune to run. I’d like to settle into the house and see how the heating system works for us, before making any decisions but don’t want to wait too long and miss out on any vat. 

 

would you have downstairs UFH, upstairs UFH, rads all on the buffer?
 

I will ask the plumber if he has allowed for weather compensation.

 

james