New Build - UFH Zones, Buffer and Active Cooling?

[Shaun McD]

Hi all, 

Couple of quick questions and looking for advise on UFH setup for a ASHP new build.

For UFH zoning;

My basic assumption is to try create individual zones for specific rooms, and leaving a large open zone something like as follows;

Bedrooms and Home office - All individual zones, i.e. an actuator on the UFH manifold attached to a adjustable temp sensor in the specific room.

Utility, Laundry, Bathroom, Ensuite, open plan kitchen/living and all hall areas setup as open loops, with their heat output controlled by the ASHP output setting?

Does this logic make sense or should I be planning to be able to control the larger space too, i.e. be able to shut it off while still supplying heat to one or multiple individual rooms?

 

Buffer tank;

With the above assumption, how do I go about figuring if a buffer tank is a good idea and how would I calculate the best size? Again by basic assumption is that the buffer tank is intended to basically increase the volume of the UFH loop as a whole, and be used to provide heat to a zone and reduce ASHP cycling? Is this correct or is there more to it?

 

Active cooling;

I have no practical experience with this, but have a very vague memory of dew points from a building services class many moons ago, so guessing that this should be a real slow burner and you would not want to actually be pumping cold water around. My basic assumption on how something like this would work;

• I am guessing I need to over ride normal room stats function, so rather than a loop which stays open until a zone hits 21c, I need the loop to stay open only when zone is above 19c for example?
• I guess then the machine is set to cooling mode and set the stop pumping when the return temp is 19c?  

Can anyone confirm how they work in practise and if my understanding is in the ballpark? 

 

TIA for any input/feedback, and please feel free to steer me on anything that I am well of the mark on!

[SteamyTea]

Generally the less zones the better, this is to stop the ASHP cycling.

To reduce cycling a buffer/volumizer or low loss header (they all do near enough the same thing) is used.  The ASHP will have a minimum volume that can be heated, part of the reason that zoning is not idea.

Dew point is a function of relative humidity and temperature.  Think of it as cold, single glazed, windows, in a stuffy house.  They are cooling the air, but due to the relatively large temperature difference, go below the dew point temperature.  If you are using the slab as a cooling element, then the temperature difference does not need to be so large, the increased area takes care of it.  There is a hand wavy, never below XX°C, but that is purely guessing.

A proper and thorough heat loss assessment needs to be done as this will take other elements such as MVHR, external temperature, target RH and the heating/cooling per m² into account.

Edited February 22, 2023 by SteamyTea

[JohnMo]

I started our heating journey similar to you, lots of zones, but after 18 months have ended with a single zone.

 

Your buffer size is defined by the smallest zone that can be in use, and the amount of water you need in the available system to give a suitable heat pump run time and allow defrosting. So the smaller the zone and bigger the heat pump, the bigger the buffer.

 

Other thing to consider is flow temperature, to get best CoP it needs to be as low as possible, so coupled with UFH both require long run times, so forme the zones did nothing just got in the way of a simple system.

[JohnMo]

8 hours ago, Shaun McD said:

am guessing I need to over ride normal room stats function, so rather than a loop which stays open until a zone hits 21c, I need the loop to stay open only when zone is above 19c for example?

If you are doing cooling get a thermostat that does both heating and cooling. Computherm for example you can select summer or winter modes.

[Shaun McD]

2 hours ago, JohnMo said:

I started our heating journey similar to you, lots of zones, but after 18 months have ended with a single zone.

 

Your buffer size is defined by the smallest zone that can be in use, and the amount of water you need in the available system to give a suitable heat pump run time and allow defrosting. So the smaller the zone and bigger the heat pump, the bigger the buffer.

 

Other thing to consider is flow temperature, to get best CoP it needs to be as low as possible, so coupled with UFH both require long run times, so forme the zones did nothing just got in the way of a simple system.

 

Thanks John, 

I have rooms with quite a bit of glazing that will get loads of sun, and a couple of rooms on the north side that will get very little so the concern would be in having balanced heating in both. Potentially adding a buffer would allow the north facing rooms to get heat while the south dont need it without cycling, which I can discuss with the installer

[JohnMo]

The thing to consider also, a well insulated house on weather comp, a 7 to 10 degree day your flow temp are likely to be circa 25 degrees.  Your floor temp is likely to be only one or so degrees higher than target room temp. Once rooms are above floor temp the UFH heating is no longer giving heat to the room.  The closer the room temp gets to floor temp the lower the floor output.  Floor heating is nothing like radiators and takes a bit of a mind set change.

 

So although it sounds odd the floor looks after its self and will start to a small degree moving heat to areas on the north side of the building if you leave the water circulation on.

[Shaun McD]

On 22/02/2023 at 11:44, JohnMo said:

The thing to consider also, a well insulated house on weather comp, a 7 to 10 degree day your flow temp are likely to be circa 25 degrees.  Your floor temp is likely to be only one or so degrees higher than target room temp. Once rooms are above floor temp the UFH heating is no longer giving heat to the room.  The closer the room temp gets to floor temp the lower the floor output.  Floor heating is nothing like radiators and takes a bit of a mind set change.

 

So although it sounds odd the floor looks after its self and will start to a small degree moving heat to areas on the north side of the building if you leave the water circulation on.

 

Makes sense. Do you know how i would go about calculating the correct buffer size? 

My initial plan will be to have a single house zone. I have the peace of mind that my home automation system will have room temps, and if needed i can future add actuators to zones which can be operated by the home automation system. I was thinking I could be very cautious and install a buffet tank as an additional 'zone', which i could then combine with room zones to bring me up to a larger volume of water when whole house heating is not required. I suppose i need to find the ufh volume of the smallest possible zone i would control, e.g. a north facing bedroom, and assume that it plus buffer needs to be suitable for the ASHP to work efficiently. Once a certain number of rooms would need heat, or the whole house needs heat, i can cut the buffer out of the system? Make sense or OTT?

[IanR]

10 minutes ago, Shaun McD said:

Do you know how i would go about calculating the correct buffer size? 

 

The Installer manual will hopefully state a minimum volume of water that must always be available to the HP for heating. My Nibe F2040-12 states 80l Min, although I have a 200l buffer.

 

12 minutes ago, Shaun McD said:

I could be very cautious and install a buffet tank as an additional 'zone',

 

If you just want to increase the volume of available water to the HP, then a 2 port buffer in the return line is generally the most efficient route. There are situations though when a 4 port buffer may be appropriate, but it does require an additional pump that may be able to be avoided without one. While air flow rates can't deliver that much heating or cooling via the MVHR, in a well insulated home there are quite a few heating days that the 1-1.5kW an MVHR can deliver is enough. A correctly sized 4 port buffer allows for an MVHR wet duct heater/chiller to use water, at ASHP flow temp, to trim house temps.

 

On 22/02/2023 at 10:48, Shaun McD said:

I have rooms with quite a bit of glazing that will get loads of sun, and a couple of rooms on the north side that will get very little 

 

I have similar and didn't fully appreciate how powerful solar gain is within an well insulated home, even though PHPP analysis told me exactly this. Thankfully I fitted external blinds to all the larger windows on the South-East and South-West elevations as they are used regularly for 9 mounts of the year to stop over-heating. In Winter, on the coldest days, which are normally the sunny days, I'll need no heating at all. I'll just let the solar gain warm up the rooms that benefit from it, then circulate the UFH to distribute that energy to the rest of the house. It does mean allowing the "sunny" rooms to get to 23°C or 24°C, but it seems nobody complains when the house is a bit warmer in winter.

[JohnMo]

1 hour ago, Shaun McD said:

Do you know how i would go about calculating the correct buffer size? 

Heat-Pump-Guide.pdf

 

Page 35 tells you how to work out system capacity required. Take away engaged volume of water i.e. smallest zone, you are left with required buffer.

 

Best efficiency comes from a volumiser, so add capacity to return side, then there is no mixing of supply and return flow.

[Shaun McD]

31 minutes ago, IanR said:

 

The Installer manual will hopefully state a minimum volume of water that must always be available to the HP for heating. My Nibe F2040-12 states 80l Min, although I have a 200l buffer.

 

 

If you just want to increase the volume of available water to the HP, then a 2 port buffer in the return line is generally the most efficient route. There are situations though when a 4 port buffer may be appropriate, but it does require an additional pump that may be able to be avoided without one. While air flow rates can't deliver that much heating or cooling via the MVHR, in a well insulated home there are quite a few heating days that the 1-1.5kW an MVHR can deliver is enough. A correctly sized 4 port buffer allows for an MVHR wet duct heater/chiller to use water, at ASHP flow temp, to trim house temps.

 

 

I have similar and didn't fully appreciate how powerful solar gain is within an well insulated home, even though PHPP analysis told me exactly this. Thankfully I fitted external blinds to all the larger windows on the South-East and South-West elevations as they are used regularly for 9 mounts of the year to stop over-heating. In Winter, on the coldest days, which are normally the sunny days, I'll need no heating at all. I'll just let the solar gain warm up the rooms that benefit from it, then circulate the UFH to distribute that energy to the rest of the house. It does mean allowing the "sunny" rooms to get to 23°C or 24°C, but it seems nobody complains when the house is a bit warmer in winter.

 

Having a buffer in the return line, does that mean that the buffer is always engaged? Or is it normal that it could be diverted around buffer? Is there a point at which having the buffer plus the full open house becomes less efficient than just the house itself? Basically going from one zone, not enough water to heat, to full house open + buffer is too much water to heat?

 

I had never thought about adding the MHRV into the mix, could you simply take a loop from the manifold to the MHRV element? Basic assumption that this would work in regular heating mode, and also work in cooling mode? 

 

Re shading, I have approached the idea of external shutters with the better half and to say I was shut down would be an understatement. The expectation that heat pump in cooling mode, plus opening windows & doors will suffice.

[Shaun McD]

7 minutes ago, JohnMo said:

Heat-Pump-Guide.pdf 1.18 MB · 51 downloads

 

Page 35 tells you how to work out system capacity required. Take away engaged volume of water i.e. smallest zone, you are left with required buffer.

 

Best efficiency comes from a volumiser, so add capacity to return side, then there is no mixing of supply and return flow.

 

Thanks for this, I can use a super basic understanding to be a PIA for the installer ha! 

[IanR]

2 minutes ago, Shaun McD said:

Having a buffer in the return line, does that mean that the buffer is always engaged? Or is it normal that it could be diverted around buffer? Is there a point at which having the buffer plus the full open house becomes less efficient than just the house itself?

 

Yes, buffer always in use. A 2 port buffer is less efficient due to standing losses of the buffer. A 4P buffer is less efficient due to standing losses + an extra pump that may not otherwise be required. Neither are huge inefficiencies. Standing losses at ASHP flow temps aren't huge, and even less at ASHP return temp (hence put the 2P buffer in the return line), plus you're only paying for one third of the standing losses since you have an ASHP heating the water. For a 4P buffer the extra pump that you may be able to avoid without it, may cost £20 - £60 a year to run. Your capital investment is also higher, of course.

 

10 minutes ago, Shaun McD said:

I had never thought about adding the MHRV into the mix, could you simply take a loop from the manifold to the MHRV element? Basic assumption that this would work in regular heating mode, and also work in cooling mode?

 

I have mine tee'd off the flow line, before the UFH group manifold, but I then need yet another pump, and use it for heating and cooling. But, energy transfer via MVHR is low, due to air-flow rates. I doubt it would make sufficient difference unless you have very low energy losses, ie. PassivHaus class.

 

14 minutes ago, Shaun McD said:

Re shading, I have approached the idea of external shutters with the better half and to say I was shut down would be an understatement. The expectation that heat pump in cooling mode, plus opening windows & doors will suffice.

 

No, HP in cooling mode will definitely not be enough. Bris Soleil is a minimum, but more control allows you to make more use of the solar gain.

What was the issue with shutters? I have external venetian blinds, that are not visible when retracted, and controlled by the HA so that the slat angle matches the suns positions to maximise visibility.

[Shaun McD]

2 minutes ago, IanR said:

 

Yes, buffer always in use. A 2 port buffer is less efficient due to standing losses of the buffer. A 4P buffer is less efficient due to standing losses + an extra pump that may not otherwise be required. Neither are huge inefficiencies. Standing losses at ASHP flow temps aren't huge, and even less at ASHP return temp (hence put the 2P buffer in the return line), plus you're only paying for one third of the standing losses since you have an ASHP heating the water. For a 4P buffer the extra pump that you may be able to avoid without it, may cost £20 - £60 a year to run. Your capital investment is also higher, of course.

 

Ok, sounds like a 2 port is the safest approach, and I can do some maths to work out the the smallest possible zone, and use that to size. Do you get such a thing as an insulated buffer? Or go about insulating myself to reduce any unintended heat loss into the zone it sits in?

 

 

2 minutes ago, IanR said:

I have mine tee'd off the flow line, before the UFH group manifold, but I then need yet another pump, and use it for heating and cooling. But, energy transfer via MVHR is low, due to air-flow rates. I doubt it would make sufficient difference unless you have very low energy losses, ie. PassivHaus class.

 

Why the additional pump? Yeah I guess the energy transfer into or out of the air would be very low, and would take a smarter person than me to do the payback for something like this

https://www.bpcventilation.com/komfovent-water-duct-cooler-heater-dhcw

Some brands seem to sell both heating and cooling options, but not sure what the difference would?

 

2 minutes ago, IanR said:

No, HP in cooling mode will definitely not be enough. Bris Soleil is a minimum, but more control allows you to make more use of the solar gain.

What was the issue with shutters? I have external venetian blinds, that are not visible when retracted, and controlled by the HA so that the slat angle matches the suns positions to maximise visibility.

 

Would you mind sending me details of brand you used? 

Hesitation from herself is on a few points;

1) We are not spoiled with lots of days of sunshine in northwest ireland.

2) The cost

3) Main living area, while south facing, has a bris soleil essentially in place with a flat roofed outdoor living area, so leave master bed and my office as the two main rooms subject to it.

4) We have had issues of overheating in the current house, which we had no active cooling, or external shades to help with so she feels we can handle it.

 

Not exactly science based, but is the world we live in. I think I may be able to get a solution over the line for those two rooms if I can find something reasonably priced and hidden. Our visit to the Internorm showroom didnt help as it was implied that internal blinds and opening windows would be enough, and that the cost for external shades was very high. Also really hurt the idea when it was said that we would only get a 2 year warranty on them ha

 

[JohnMo]

1 minute ago, Shaun McD said:

Why the additional pump

Because a 4 port buffer (connected to flow and return) acts as a hydraulic break in the system.  Without the additional pump the water would just flow from the HP to buffer and back to HP.

 

A volumiser come insulated and without.  Grant do some nice insulated volumisers.

[IanR]

47 minutes ago, Shaun McD said:

Ok, sounds like a 2 port is the safest approach, ... Do you get such a thing as an insulated buffer? Or go about insulating myself...

 

As long as I've explained well enough. A 4P buffer is a different use case, ie. if you want/need to run separate heat/cooling system (wet duct MVHR or fan coil heater/chiller) and you want to run that at ASHP Flow temp, for as long as possible when the ASHP is not running, then you need a 4P Buffer. If you "just" want to increase the volume of available fluid to the ASHP, then a 2P Buffer in the return line. Yes the Buffers are available pre-insulated, and there's no harm adding more.

 

47 minutes ago, Shaun McD said:

Why the additional pump?

 

For my MVHR Wet Duct? Because I tee off the flow line before it gets to my UFH group manifold, which holds the UFH pump. So to get flow through the MVHR wet duct heater and back to the buffer, I need a pump on that loop. I had to do it like this as I wanted to be able to shut the buffer off from the UFH and just circulate the UFH water to re-distribute solar gain from the warm side of the house to the cool side. So this is rather specific to my installation and there may have been a better way of doing it.

 

47 minutes ago, Shaun McD said:

Some brands seem to sell both heating and cooling options, but not sure what the difference would

 

A condensate drain. So I use a wet duct chiller for mine which either heats or cools the MVHR based on what's in the buffer.

 

47 minutes ago, Shaun McD said:

Would you mind sending me details of brand you used? 

Hesitation from herself is on a few points;

1) We are not spoiled with lots of days of sunshine in northwest ireland.

2) The cost

3) Main living area, while south facing, has a bris soleil essentially in place with a flat roofed outdoor living area, so leave master bed and my office as the two main rooms subject to it.

4) We have had issues of overheating in the current house, which we had no active cooling, or external shades to help with so she feels we can handle it.

 

Mine are Hunter Douglas external venetians and colour match very well to my Alu-clad Internorm windows.

 

Good point regarding your location. And maybe your shading to the living area. I wouldn't take a risk on this though and I'd get it modelled. I'd recommend PHPP even if you don't plan to build to a PassivHaus level.

 

Costs for me we're offset to some extent by not needing such expensive internal blinds/curtains. In my living areas I having nothing internal on the windows, and in bedrooms I have internal roller blinds. 

 

When my blinds are retracted they are entirely concealed behind the cladding

 

In 2017 the 5m window blinds were £2K each and I have some 2m windows that were £1K each. Internorm wanted around £1K per sash, but they do add a 4th pane when they include integral blinds.

 

 

 

Edited February 24, 2023 by IanR

[Conor]

You're in Donegal, you'll not need to worry about active cooling. We used ours for a few days in the July heatwave and that was it. You'll not need much in the way of external shading either. Spend your money on better glazing instead, and dont put too much on your southern elevation.

 

PHPP told us we needed all sorts of shading, was coming out at £6k. We winged it and didn't bother, depeened window reveals a bit, extended a couple roof over hangs and seems to have coped well.

 

Fact is, even if you do get really high daytime temps, that close to the Atlantic you'll easily be able to cool the house down in the evening by opening a couple big windows. And on the odd occasion that's not enough, your UF cooling will do the job, and just set it manually to during the day and your PV will run it for free! Makes no sense at all to spend thousands on shading and shutters.

 

In our coolenergy system it's all setup and programmed to go, just a matter of selecting the cooling mode on the control and setting the timer. Don't worry about controlling it with room stats or anything, just have it on from 11am to 6pm and let it do its thing, it won't get too cool as your flow temp will be 12c or so.

Edited February 24, 2023 by Conor