ASHP advice on buffer tank / heat store and more

[Joyosa]

Hi All

I am looking for some advice on improving the design of an existing ASHP setup.

 

Sorry for the long intro.

 

Originally the setup had a big 56kW HP feeding buffer tank & DHW, coupled with a gas boiler. The system runs both UFH and radiators. I was going through stupid amounts of gas, just to have enough water to have a bath.

I ended up scrapping the gas boiler altogether and replacing it with a heat pump hater water cylinder, which paid for itself in 3 months. So now the main heat pump just does heating. 

We have also recently had a Linky (French Smart Meter) installed, which seems to have made the metering of electricity used go up dramatically. Also to add to the equation, our tariff has a red period - where the cost is 5 times normal (for 24 days a year) - these days we actually shut off the HP and just use the fire place.

 

My plans are:

 

1. Install a large buffer tank (2000 litres) - existing is 300L, to be used as a heat store, to heat radiators and UFH, even when Heat pump is off (Red days). I have read that buffer tanks are actually inefficient, or that they have a relatively small maximum size to be used. Also I think this will dramatically reduce cycling when heat pump is on.
2. Connect the ASHP through a 3 phase condenser to the reduce the electrical loads and power factor that the Smart meter senses.

 

I can add some pictures a further details a bit later

 

I was just wondering if these plans seem reasonable or if I am barking up the wrong tree. Any advice will be gratefully recieved - Thanks in advance

[JohnMo]

Are you sure you have a 56kW heat pump? If so you must be heating a castle.

 

2000L will contain 46kWh with a start temp of 55 and dropping to 35 degs. So not much, plus you take a huge CoP hit heating to that temperature, so why bother.

 

Think you need to think simple. I would say dump the buffer altogether, if you need more water volume (approx 20L per min kW output of heat pump), use existing buffer as a volumiser for heating system. So connect in supply or return line not both. You can delete the secondary pump. You need to look at zoning also, i.e. remove as much zones as possible and the ones that exist make as big as possible. You want heat pump running low and slow all the time generally - not the red days obviously.

[Joyosa]

Thanks for the feedback - mine is the model 060 so 57kW heating - it is a big drafty place. So you think, I should go for 2 zones (UFH and Radiators). Presently there 5 or 6 zones, which I am sure I can simplify. I guess I have a lot more studying to do. The data sheet says 143 litres, minimum loop volume - 600L max - does this mean I should be trying to size all pipework, radiators and UFH for this min volume, then work back for pipe friction losses, for pressure and flow of pump?

 

Sorry if these seem daft questions, only just starting the adventure.

[sharpener]

59 minutes ago, Joyosa said:

Connect the ASHP through a 3 phase condenser to the reduce the electrical loads and power factor that the Smart meter senses.

 

This may work if the HP is an old one with the compressor driven by a plain old 3-phase motor. But all modern HPs have inverter drives which will present a power factor close to 1.0 so no scope for improvement.

 

I am still puzzled by the size of yr HP, this must be a record for anyone posting to this forum. What make/age is it?

[Wil]

Yup beats my two ASHPS adding up to 42kWp. Looking forward to the floorplans. And how on earth you get that heat into the space. 🙂

[Conor]

Spend a bit of effort on making it less big and drafty.

 

with an indicated heatloss 10x bigger than what we're used to seeing here, I don't think the normal assumptions apply here.

 

I've looked up the datasheet for your heatpump. The first thing that jumps out at min is the min flow rate of 1lp/s. I don't see you you can achieve this through UFH loops in  a normal domestic setting. You'd be needing around 10km of loops across 40+ individual loops. Is this what you have?

Edited Thursday at 12:39 by Conor

[Joyosa]

It is an old one, think installed around 2006/7. Plain 3 phase, with no inverter. It is a Carrier 30RH-060-B0358-PEE. She is certainly a big old beast.

13426_IOM_12_2008_30RH_LR.pdf

[Gary68]

Its nearly 20 years old, at the end of its serviceable life, are you not better off starting from scratch with a modern heat pump and redesigning the heating system as best you can.

[Joyosa]

It probably is. 

[Joyosa]

1 hour ago, Conor said:

Spend a bit of effort on making it less big and drafty.

 

with an indicated heatloss 10x bigger than what we're used to seeing here, I don't think the normal assumptions apply here.

 

I've looked up the datasheet for your heatpump. The first thing that jumps out at min is the min flow rate of 1lp/s. I don't see you you can achieve this through UFH loops in  a normal domestic setting. You'd be needing around 3.5-5km of loops. Is this what you have?

I don't think my floor is quite that big. I guess that is the reason the tank is there. 

[Gary68]

I think you need to go back to basics get someone to work out the heat loss for your house or do it yourself on the heat punk website then you can determine what your options are.

 

Have you any idea why a 56kW heat pump was installed 19 years ago?  It could be massively oversized like boilers are, you may only need something half the size or less.

 

Why do you have a 300L buffer tank they are usually installed to keep oversized heat pumps happy with good flow rates which leads back to the first question.

[Marvin]

5 minutes ago, Gary68 said:

I think you need to go back to basics get someone to work out the heat loss for your house or do it yourself.

A must.

Edited Thursday at 15:24 by Marvin
minor change.

[Nickfromwales]

4 hours ago, JohnMo said:

use existing buffer as a volumiser for heating system

May be an issue if the DHW cylinder coil cannot cope with the amount of heat / flow from the T-Rex of a heat pump that is installed here. It may need the buffer for DHW too?

[JohnMo]

18 minutes ago, Nickfromwales said:

May be an issue if the DHW cylinder coil cannot cope with the amount of heat / flow from the T-Rex of a heat pump that is installed here. It may need the buffer for DHW too?

From original post

 

5 hours ago, Joyosa said:

heat pump hater water cylinder, which paid for itself in 3 months. So now the main heat pump just does heating. 

Heating and hot water are different heat pump - or at least that's what I read?

[JohnMo]

2 hours ago, Joyosa said:

don't think my floor is quite that big.

Something isn't correct, I would start with a decent heat loss calculation and go from there. Big rambling pile with a wall missing maybe 50+kW, but would more likely suspect way smaller.

[sharpener]

3 hours ago, Joyosa said:

I don't think my floor is quite that big. I guess that is the reason the tank is there. 

 

It would be helpful to tell us the overall floor area and the general nature of the construction. Then you can get a very approximate estimate using the heat geek crib sheet.

 

But IMO much better to start again using a modern R290 unit than throw money at upgrading such an old setup.

[Joyosa]

14 hours ago, JohnMo said:

From original post

 

Heating and hot water are different heat pump - or at least that's what I read?

Yes, I have now separated them. The water tank is what they refer to as Thermodynamique over here, similar to this : https://www.ariston.com/fr-fr/produits/chauffe-eau-ballons/chauffe-eau-thermodynamique/nuos-primo-hc/. Basically runs only at night, on cheap rate electricity, with a built in heat pump on top. So now the Main heat pump is only doing the heating of the house and a granny flat.

[Joyosa]

It is an old stone building, probably parts dating back to 1700s. I think the footprint said 350m^2 but I do not recall whether that is for the main floor, or the others - will spend some time at the weekend, do some proper investigation.

 

The house was probably renovated around 20 years ago, when the heat pump was put in. Essentially I see 4 or 5 zone pumps including 1 for UFH, plus a really big heat exchanger, that goes to a pool - I have never used that circuit, pool capacity about 100 m^3.

 

I think the advice seems to be do a proper heat calculation on the place and then see about a new HP or 2.

 

Really appreciate all the advice so far from all of you.

[JohnMo]

Starting to make a little more sense now

 

Pool on its own could be about 8 to 20kW of the heat pump capacity.

 

House is big and old, how big because you say footprint - so is 700m² or 350m² or is it many storeys high and way bigger than that?

[Joyosa]

12 minutes ago, JohnMo said:

Starting to make a little more sense now

 

Pool on its own could be about 8 to 20kW of the heat pump capacity.

 

House is big and old, how big because you say footprint - so is 700m² or 350m² or is it many storeys high and way bigger than that?

House has 3 floors, without Granny flat. However a little hard to detail, as it has been cobbled together over the years. I think I will need to put is a sketch to make it clearer, but certainly some large volumes.