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rt29781
26-11-2009, 04:21 PM
Hi, we lve in the SW of France and have just bought a 12kW air to water heat pump from Trianco. Its a fully configured system not a split system. All I have got to do is connect the system into our current heating system. At the moment we have 150 evacuated tubes on our roof. These capture the suns heat and then the heat goes into our underfloor system via a heat exchanger. That bit works fine when the sun is shining and it shines about 300 days a year here. However when it is cloudy we want more comfort so we bought the heat pump. The heat pump requires a 28mm pipe connection. I was going to put 10 m of 28mm pipe onto the flow and return of the heat pump and use 7m of that loop as the heat exchanger. The heat exchanger will sit in our 500 lites tank at the bottom.

My question is: Is 7 m of 28mm pipe sufficient to transfer 12 kW of heat?

Typically the tank will be at 20C in the morning when the heat pump comes on then the heat pump should take about 2 hrs to raise the temperature to 45C when the underfloor heating willl start to remove the heat. If we get solar gain then the heat pump will shut off as the heat rises above 55C.

mad fridgie
27-11-2009, 07:43 AM
What is the tank used for, (the fluid in the tank) Is soley for heating or do you use it for DHW (hot tap water)

rt29781
27-11-2009, 12:16 PM
What is the tank used for, (the fluid in the tank) Is soley for heating or do you use it for DHW (hot tap water)
The tank is used for domestic water heating but only via a copper loop. So instant hot water rather than water drawn from the cylinder ie no risk from legionella. The tank has 4 copper loops:
A pre heater for the underfloor heating before the Zilmet solar heat exchanger (10m 16mm copper) (top of tank)
A scavenge loop from the solar (10m 16mm copper)(top of tank)
The instant hot water loop (10m 16mm copper)(top of tank)
The proposed heat transfer loop from the heat pump (10m 28mm pipe) (bottom of tank).

In normal solar operation only the top of the tank gets warm. This means in winter we have effectively a smaller tank when using solar heat as we get stratification (hot at top, cold at bottom). I envisage for heat pump use to put the transfer coil at the bottom of the tank to heat the whole tank. Comments welcome.

DEVIL
27-11-2009, 12:58 PM
1 the heat pump u bought is to large for your tank
2 for your pump u need a minimum of 1,5 m2 of heat exchanger

So .... you have on 28 mm pipe = 0,0879 m2 / m rezulting from this 0.879 m2 on 10 m pipe length.

With this heat exchanger your heat pump will short cycle and not work in the designed COP, and use more electricity then needed.

You would need a minimum of 15 m of 28 diameter pipe.

I don't know how large your water usage is, but for a normal family of 4 , (2 adults and 2 kids) a heat pump of 6 Kw would be more then enough because u have the storage tank, and for 6 Kw your initial idea for the heat exchanger would be enough.

But u didn't sent any infos about the size of the underfloor heating, and building specs

rt29781
27-11-2009, 05:29 PM
Hi Devil,
The supplier Trianco said that 300 litres was a big enough tank. Ours is 500 litres, so I am now confused. We have 250 m2 of floor area served by the underfloor heating but routinely only use 120m2. The system is mainly for heating the house not the water for showers etc. Thanks for the specification for the heat exchanger. I can easily make it 15 metres of 28mm pipe. The house has reasonable insulation and is mostly double glazed (all windows also have wooden shutters so effectively triple glazed when dark)and in our part of SW France it rarely goes much below freezing for long (near the Mediteranean). Perhaps I will only run the pump in the morning to get the house warm and then see if the solar is going to keep the temperature ok. If no solar I can manually intervene.

mad fridgie
27-11-2009, 07:46 PM
Good explanaion,
You do "not" want use the heat exchanger as you have designed.
If your primary use is for the underfloor heating then heat directly the water that is going threw the underfloor with the heat pump.
Without knowing the full design of the system, I give what i think is.required.
You need a 50mm pipe about 1 meter tall.
Draw water from the bottom of this pipe to the heat pump, return to the top of this pipe.
Draw water from top of pipe to your underfloor, return to UF coil in the cylinder, from the cylinder,back to bottom of pipe. or
return UF directly to bottom of pipe,
Connect from top and bottom of pipe, to 2 heat exchangers install pump and change overvalve. This valve is there control if you want remove enregy from the tank or you want to add energy to the tank.
I have presumed that the actual fluid in the tank is static and that you do not want to pump this, as you maybe concerned that the stratification will be reduced

rt29781
27-11-2009, 09:15 PM
Good explanaion,
You do "not" want use the heat exchanger as you have designed.
If your primary use is for the underfloor heating then heat directly the water that is going threw the underfloor with the heat pump.
Without knowing the full design of the system, I give what i think is.required.
You need a 50mm pipe about 1 meter tall.
Draw water from the bottom of this pipe to the heat pump, return to the top of this pipe.
Draw water from top of pipe to your underfloor, return to UF coil in the cylinder, from the cylinder,back to bottom of pipe. or
return UF directly to bottom of pipe,
Connect from top and bottom of pipe, to 2 heat exchangers install pump and change overvalve. This valve is there control if you want remove enregy from the tank or you want to add energy to the tank.
I have presumed that the actual fluid in the tank is static and that you do not want to pump this, as you maybe concerned that the stratification will be reduced

Hi mad fridgie, the water here is very hard so I don't want a large volume flowing through the heat pump. The tank is open and vented so needs topping up with tap water hence danger of scale. Also the heat pump manufacturer forbids direct connection to the underflloor heating system and recommends a buffer tank either direct or indirect. So this is why I want to use a sealed indirect coil in a large tank rather than just hooking up the system to the underfloor system. Also I do not want to interfere with the solar heating side of things. Also I want to heat up the whole 500 litres and then drain that heat into the house. In this way I can heat the water on off peak electricity.

As a side benefit we will get warm water from this tank and that feeds into our domestic hot water that is topped up by an immersion heater that runs at night.

I am sorry it is so complicated, can I post a diagram on this forum?

Is there a problem connecting say 20m of 28mm pipe to the heat pump as a bottom coil in the 500lt tank? The manufacturer recommends a 28mm pipe to achieve a flow rate of 33lt/min.

If I understood your system correctly I have a 1m 50mm pipe sitting in my tank. Water from the heat pump enters the 50mm pipe at the top and leaves it at the bottom. I then also pump water from the top of this pipe to the underfloor system and return the underfloor flow to the bottom of the 50mm pipe. I presume very little heat would be passed from the 1m pipe into the water tank as it has a small surface area. If I used this system how would the solar system interact with it?

mad fridgie
27-11-2009, 09:56 PM
The 50mm is external to the tank,
The system is closed loop, so water quality is not important (apart from first charge)
The reason for the pipe is to allow for inbalance in water flows.
The heat pump MUST always have the correct flow. The heat pump water pump must not be used directly for the flow to the under floor (Unless you really now what you are doing)
I gave you an option for heating the tank via change over valve, this way youhave 2 heat exchanges to transfer the heat.
So the water in the tank is as is now.
Remember that 500L as far as heating goes stores very little energy. With a heat pumpas the water becomes hotter the efficiency drops considerabley (For every 1C your water rises you use 3.5% more power, for you fridgies out there I just converted SCT change to a more practical understanding)
As far as pipe sizing you can use what ever you want, you just need to know the pressure drop and size the pump to suit. (would advise that you keep internal piping velocity to be under 2.4M/s)
I hope that helps

DEVIL
27-11-2009, 11:03 PM
So ... let's make everything clearer by starting from the top

We are talcking about a buffer tank
And in the buffer tank for your needs you would need 4 heat exchangers coming in this order from the top of the tank:

-the Domestic Hot Water (DHW) ending on the top but beginning some were close to the bottom
- the underfloor coil from the bottom of the tank to the 3/4 of the tank
- the Solar coil from a little bit lower then 3/4 to the top
- the heat pump coil from the bottom to the 3/4

The coils overlap like this

The solar coil overlaps in large amount with the DHW , and a little bit of the heating (so that the priority is for the DHW)

The heat pump coil overlaps with the heating and a little bit with the DHW (because it's cost efficient for the solar to heat the DHW at a higher temp. and not the heat pump in low solar situations)

The DHW start at the bottom so it's pre heated from the colder side.

- This is a standard buffer tank, in your case it might be a little changed, but i recommend to get as close as possible to the standard.

The water enter in any coil lower temp an the lower side and higher temp at the upper side.

And 15 m is the minimum, i would recommend 17-20 m (for 12Kw)

rt29781
28-11-2009, 07:28 PM
Hi Devil,

Thanks for the clarity, all of my three current coils are in the top third of the tank for a reason. I will put the 20m coil down the centre of the current coils if I can get it in. Getting 20 m of 28mm pipe in the tank will be a challenge as the tank is only 1m high.

Hi mad fridgie, I am begining to think of the 50mm pipe as a super bypass. What material do you use for the 50mm pipe? Copper, plastic? Not sure that it will be easy to get 50 mm copper here in France. Will thick walled pool quality plastic take the pressure? I also like the idea of running the system at the lowest temperature although the lowest temperature the pump will seek for is 40C. Certainly today the sun was out and the solar had the floor temperature at 30C but the house is lovely and warm. The 500 litres should store 25kW which would warm the house in the morning. It would take the pump 2 hrs about to heat the tank from 20C to 40C.

mad fridgie
29-11-2009, 04:29 AM
Hi Devil,

Thanks for the clarity, all of my three current coils are in the top third of the tank for a reason. I will put the 20m coil down the centre of the current coils if I can get it in. Getting 20 m of 28mm pipe in the tank will be a challenge as the tank is only 1m high.

Hi mad fridgie, I am begining to think of the 50mm pipe as a super bypass. What material do you use for the 50mm pipe? Copper, plastic? Not sure that it will be easy to get 50 mm copper here in France. Will thick walled pool quality plastic take the pressure? I also like the idea of running the system at the lowest temperature although the lowest temperature the pump will seek for is 40C. Certainly today the sun was out and the solar had the floor temperature at 30C but the house is lovely and warm. The 500 litres should store 25kW which would warm the house in the morning. It would take the pump 2 hrs about to heat the tank from 20C to 40C.
Hi firstly your tank with a 20C temp difference is only 11.6Kwhr, and really to be usefull for heating min temp, so real storage is lower.
the 50mm pipe is a stratified balancing pipe. (nothing more than allowing pumps to flow at different rates)
The height is to allow maximum temp differnce.
Can it be made of plastic, yes it can as long it is rated to your max temp. (can be made galv steel, S/S, your system should not be under great pressure)
Re- floor temp , this more about your floor covings (carpets, etc) than the heating system, if you just have polished concrete, the 26C isnormally enough (this personal though)
Another way of reducing your system temp is to icrease the flow through the under floor, reducing the split between in and out, (many of my systems we only supply 30-32C, return (off temp) 28C

DEVIL
29-11-2009, 10:17 AM
Wat mad fridgie stated is true, at a 20 K u can only store a maximum of around 12 Kw is your tank is the same temperature from top to bottom.

And 30-35 is the typical temperature u should go in underfloor heating.

But if u can use the stratification effect, u can have on the bottom 35-40 deg C for the underfloor (water in tank, not output), and on the top, 50 deg for the DHW , and overlap a little bit of the coils so u can use any of the heat source (solar, or heat pump) for heating and preheat DHW with the cost efficient 35 heat pump sourced water.

rt29781
29-11-2009, 07:10 PM
Hi Devil/ mad fridgie,

I am concerned at the cost of the 20m of 28mm copper pipe so I have another possible solution. Use 1 meter lengths of 10cm pvc soil pipe. These pipes are closed at one end. At the other end they have a 40mm outlet at the side and a 1.1m 40mm pipe through an end plate. So the 40mm pvc goes near to the bottom of the 10cm pipe at the closed end. The flow goes down the 40mm pipe and up the wall of the 10cm pipe then out of the side exit. In this way I can put as many of these pipes in my tank as I need and each pipe has a surface area of about a third of a metre. So six tubes would give me a heat exchange area of 1.8m2. Now you may be thinking that PVC is an insulator and so was I but read this which compares iron pipe to thin PVC pipe:
-------------------

As to the middle term, the conductivity of the tube material itself: Standard iron pipe of 1/4" thickness has a conductivity of around 1480 Btu/hr/sq.ft./F. The PVC plastic pipe we are recommending has a much lower value, and would only be around 48 Btu/hr/sq.ft./F for a 1/4" thick wall (Schedule 40). We selected the thin wall drain pipe to enable this to be around 120
Btu/hr/sq.ft./F for our choice of material. As we will see, the difference in this term between 1480 and 120 and 48 is nearly irrelevant, because both of the film coefficients are far lower and they always represent the limiting cases.

Now, let's calculate U. If we used (relatively expensive) iron pipe, we would have:
1/U = 1/13 + 1/1480 + 1/100, which gives U as 11.4 Btu/hr/sq.ft./F.

If we use the (thinwall) PVC tubing we recommend, we would have:
1/U = 1/13 + 1/120 + 1/100, which gives U as 10.5 Btu/hr/sq.ft./F.
----------------------
So in this way I can daisy chain these heat exchangers in my tank. I can also take off and feed in my flows from the underfloor system if I wish. The 40mm pipes can be connected to the heat pump and offer good flow. characteristics. All connections are made at the top which is good for my top opening tank. So its a bit like a tank in a tank.

What do you think? It was mad fridgies balance tube that set me thinking.

Pvc is good to 60C with a maximum of 80C so thats ok as the tank has an auto cool set at 59C. I can run this at 10 psi which will be ok.

mad fridgie
29-11-2009, 07:51 PM
I really do not understand your facination with the storage tank, we have explained it has very little use as far as thermal storage for heating.
Remember when you have cheap power at night, it is also cold at night, so your heat pump is not working as efficient, store the energy from the heat pump directly in the floor.
As far as scavanging heat from the solar system, again the system allows for this.
Its a pitty yoour tank is short, you would have been better with a Tall and skinny one, a few more tricks coulds have been achieved.
As far as cost, you have spent plenty so far, it would seem stupid to spoil all your efforts, by at the end cutting a few corners.

rt29781
29-11-2009, 09:01 PM
Hi mad fridgie, I am not good at spending money I don't need to, hence why my tank cost 50 euros rather than 2000 euros for a tall skinny bought one.....I cannot see a way to get my solar circuit linked up with the heat pump without the tank unless I put antifreeze in the underfloor loops and I don't want to do that. I have to have antifreeze in the solar high temp loop and in the heat pump loop. The rest are just water as there is no problem if they freeze.

I do agree that putting the heat in the floor is the best option.

mad fridgie
29-11-2009, 09:24 PM
In one of my earlier threads, I explained how (or may be not well enough)
I think you under stand the balancing pipe I suggested! (heat pump and underfloor sorted)
Right you take another leg of the bottom, up pump this water through your existing underfloor loop (and the new HP loop if you want to install) in your tank, you reintroduce the heated water to the top of the pipe.
You then can scavage the solar heat.
By reversing the flow of this loop you can pre-heat the cylinder with the heat pump. (all singing and dancing version)
Then you have to decide the method of control, from a simple thermostat, to smart logics.

mad fridgie
29-11-2009, 09:27 PM
Why do you have anti freeze in your heat pump loop?
Solar loop yes with anti-freeze.
Remember that every level of transfer will cost you at least 15% extra in power.

rt29781
30-11-2009, 12:15 PM
The heat pump is outside (air to water). It may get below freezing. We may have a power cut if the overhead cables ice up. Then we have a burst heat pump. Do you not get freezing conditions in New Zealand or is the power never off? Unfortunately we get freezing conditions and we get powercuts if the cables ice up. Doesn't happen often but only needs to happen once.

mad fridgie
30-11-2009, 08:08 PM
The heat pump is outside (air to water). It may get below freezing. We may have a power cut if the overhead cables ice up. Then we have a burst heat pump. Do you not get freezing conditions in New Zealand or is the power never off? Unfortunately we get freezing conditions and we get powercuts if the cables ice up. Doesn't happen often but only needs to happen once.
Yes we have power cuts and gets well below freezing (-6 to -10C), if your pipes and heat exchangers are well insulated then there is little or no chance of freezing (which they should be)

rt29781
01-12-2009, 12:07 PM
Hi mad fridgie,

Well the pipes are going to be PVC now so they will take a freeze, in that case I will have a go with your balance pipe. I will also insulate the pipes. So I will have a circulation pump on the heat pump circuit pushing the water to the top of the balance pipe (50mm PVC).The water returning to the heat pump via the balance pipe. Then I will have a connection from the underflloor flow after the underfloor circulation pump at the top of the balance pipe and a connection 180degress from this pipe to the underfloor loops. The return from the underfloor loop goes to the bottom of the balance pipe and 180 degrees from this returns to the preheat and underfloor heat exchanger. My question is if the underflloor pump is off will the heat pump circulation pump be enough to push water through the underfloor loop?

So just to clarify I have 3 standard circulating pumps. One on the high temp solar circuit (Propylene Glycol). One on the existing underfloor circuit (water). These 2 pumps push liquid around the Zilmet heat exchanger to grab the heat from the solar panels pushing it straight under the floor, and are controlled by a Resol Deltasol M controller. This is independent from the heat pump that has one circulating pump. If the solar pumps are off the heat pump circulating pump will push water through the balance pipe but will it also flow through the underfloor loops? If it does great. If not the heat pump has nowhere to lose the heat. The supply to the underflloor system uses 25mm polyethylene irrigation pipe. My worry is the back pressure of the underfloor system will prevent a flow as the circulation from the heat pump will prefer to go down the 50mm balance pipe.

If you agree that this is the system that you would use I will build it and see what happens.

Many thanks for your patience and advice.

mad fridgie
01-12-2009, 07:05 PM
For simplisity, I would have a dedicated pump between the balancing pipes and the heat exchangers within the tank.
The heat pump water pump will not pump water through any of the circuits, only through the balancing pipe. This applies to all pumps connected to the balancing pipe.
(Do not know your heat exchanger or controller, so can not be specific)
I would also use the heat from your heat exchanger via the balancing pipe.
Your balancing pipe is common control point.
I have my heat pump control thermostat sensor at the bottom of ths pipe.
How you choose to control has many options, for me personally being warm is the main driver, not pure efficiency, but have designed systems when priority is the other way around.
One thing I always do is install a larger water pump than most on the underfloor circuits, this allows for small delta T and very even floor temp (practically allowing for a lower setpoint) I have seen many UF systems failbecause they have used a boiler design (higher inlet flow temps) then just thrown on a heat pump (lower inlet flow temps)

rt29781
01-12-2009, 09:32 PM
Hi mad fridgie in our currentl design our underfloor heating circulation pump is before the proposed balance pipe. It looks like it needs to be on the exit pipe at the top of the balance pipe, pulling warm water from the top of the balance pipe and pushing it to the underfloor circuits? Our controller is a very sophisticated bit of kit so it will control the system no issues. I think I will leave the return from the underfloor system as it is. If it goes to the bottom of the balance pipe it will just go around the heat pump circuit.

mad fridgie
01-12-2009, 10:00 PM
Your underfloor pump should actually be on the outlet of the underfloor, (reduces chance of cavitation and helps keep the motor cool) which then feeds the bottom of the balancing pipe.
In a perfect world the balancing pipe does nothing, but the chances of balancing flow rates , is near on impossible especially if you are looking at zone control

rt29781
02-12-2009, 04:16 PM
Hi mad fridgie, you are right but I have three underflloor manifolds, a swimming pool and a jacuzzi all of which get heated by this system at some time. So I push the water around the system from the business end and it works fine. Otherwise I would have 4 more pumps than I currently have. Its a big system with a lot of interfaces.
see our blog http://smartfrance.blogspot.com. Anyway I will await the heat pump and feedback to you.

rt29781
23-01-2010, 08:46 AM
The heat pump has arrived and it is fitted. It works really well and complements the solar heating system. details and output figures are on our blog http://smartfrance.blogspot.com
We have a leak in the PVC heat exchanger but it is nor serious. The end fittings on the 10cm sol pipe screw on and don't take the pressure (they need welding). I will fix it at some point....

Many thanks to all those that gave advice. At some point I will convert the system so the heat exchanger can be taken out of the loop (fit isolation valves) leaving just a balancing pipe as suggested by mad fridgie, this will work better in cold weather making sure all the heat goes into the floor.

The heat pump sure makes the lights dim. Has anyone got any experience of soft start systems that prevent the lights dimming?