UFH - Wiring Requirements

[Barney12]

Another first fix question from me. You can tell I'm starting to triple check before boards start flying up!

 

Ref UFH manifolds: Only one zone but as we're split level we have two manifolds. Upper one is in the plant room so no drama's there.

Lower one is in the under-stairs cupboard.

 

So far to the under-stairs manifold location I've run:

 

22mm feed and return

1.5mm 4 core for the pump power and control

1mm 2 core for the actuators

 

Is that all I need?

 

The room thermostat is actually on the CBUS network so that's CAT5 and independent to the heating system. The CBUS network will trigger a relay to signal for heat (actual system still not finalised so a bit woolly here!).

 

I'm also wondering if it would be better to site both pumps in the plant room?

 

 

[le-cerveau]

If you only have one zone, why the actuators? Won't you be running the whole thing together (as Jeremy does) or not at all, so surely the actuators are nugatory?

[joe90]

I am only having one zone but the spark has run spare cables to plant room, manifold, airing cupboard , "better to have spares than run out" quoting the spark!.

[ragg987]

11 minutes ago, le-cerveau said:

If you only have one zone, why the actuators? Won't you be running the whole thing together (as Jeremy does) or not at all, so surely the actuators are nugatory?

Exactly - also why the local pump, you could run both manifolds off one centralised pump. If yours is a low energy house you will easily have sufficient flow with 1 pump at the lowest speed. In our case one slow pump serves 2 manifolds (basement and ground) over 150m2 at 150 pipe centres.

[le-cerveau]

@joe90 Agree with the spare cables, but actuators cost money and add un-necessary complexity.

[Barney12]

2 hours ago, le-cerveau said:

If you only have one zone, why the actuators? Won't you be running the whole thing together (as Jeremy does) or not at all, so surely the actuators are nugatory?

 

Good point! Its my sparkies fault he started listing all the cable requirements he usually allows for.

[Barney12]

2 hours ago, ragg987 said:

Exactly - also why the local pump, you could run both manifolds off one centralised pump. If yours is a low energy house you will easily have sufficient flow with 1 pump at the lowest speed. In our case one slow pump serves 2 manifolds (basement and ground) over 150m2 at 150 pipe centres.

 

Hmmm. Now this idea I like.

[ragg987]

Yes you need to watch the trades - they know what they know. I gave my plumber our installation diagram and details as well as talked it through with him. I was clear that the manifolds were to have no pumps or actuators. A couple of weeks later he asked the sparkie to provide power at the manifolds, luckily the sparkie checked with me (he knows how particular I am) and we put a stop to this. Aaargh.

[Nickfromwales]

2 hours ago, ragg987 said:

Exactly - also why the local pump, you could run both manifolds off one centralised pump. If yours is a low energy house you will easily have sufficient flow with 1 pump at the lowest speed. In our case one slow pump serves 2 manifolds (basement and ground) over 150m2 at 150 pipe centres.

I don't really like that idea tbh as balancing flow between the two manifolds could be an issue if they're far apart. 

In Barneys case they're on different levels too. 

[ragg987]

I can only relate our experience. One manifold is next to the pump in the plant room, it has more loops connected and serves 100m2. The other is in the basement and serves 50m2. I have balanced the inconsistent demands by twiddling the manifold flow knobs. Ground is fully open and basement is partially throttled.

 

It works. I believe largely because of the very low temp flow and gentle heating possible in a low energy house.

[Barney12]

2 hours ago, Nickfromwales said:

I don't really like that idea tbh as balancing flow between the two manifolds could be an issue if they're far apart. 

In Barneys case they're on different levels too. 

 

OK< so assuming a pump at the second manifold and no actuators; all I need is a 3core and earth?

[Nickfromwales]

7 hours ago, ragg987 said:

I can only relate our experience. One manifold is next to the pump in the plant room, it has more loops connected and serves 100m2. The other is in the basement and serves 50m2. I have balanced the inconsistent demands by twiddling the manifold flow knobs. Ground is fully open and basement is partially throttled.

 

It works. I believe largely because of the very low temp flow and gentle heating possible in a low energy house.

I can see it would work, just that altering any one port effects the balancing on both manifolds, a bit like folk are saying they have to go back and forth balancing their entire MVHR after adjusting just one outlet.  . 

Also, when your blending the UFH flow the pump usually sucks through the TMV, so where / how do you blend the UFH flow temp ?

 

[Nickfromwales]

7 hours ago, Barney12 said:

 

OK< so assuming a pump at the second manifold and no actuators; all I need is a 3core and earth?

Not even that, just live, neutral & earth and that's it for the pump, no need for the fourth core.

Dont fotget you'll need a 2-port valve for each manifold, to stave off convection heat circulation, and wherever you put those you will need a cable too. The stat or timeclock should tell the 2-port valve to open, by energising the brown wire, and the switched pair ( orange and grey ) in the 2-port should control the manifold pump. Basically that means the pump will never run unless the 2-port is fully open. You don't just connect the 2-port and the pump off the same 'call for heat' terminal or the pump will spin before the valve is open. Not life or death as a true manifold setup will recirculate, but standard practice. 

[ragg987]

9 hours ago, Nickfromwales said:

Also, when your blending the UFH flow the pump usually sucks through the TMV, so where / how do you blend the UFH flow temp ?

 

No blending required. The ASHP regulates the flow temperature. I have a 90l buffer to reduce cycling.

[Jeremy Harris]

What's the minimum flow temp of the ASHP?  Mine just won't regulate at all below about 30 deg, and even then it jumps up and down by 3 or 4 degrees.  If the flow temperature to the UFH exceeds about 24 deg C then we get big temperature over-shoots in the house, even with room thermostats with 0.1 deg switching hysteresis, so I have to make sure that the TMV can accurately hold the flow manifold temperature at the relatively low set point.  This was one of the hardest parts to get right, getting really tight control of the UFH flow temperature, and realising it's significance in house temperature stability control.

 

I also use the buffer to preheat the DHW, so wanted that as hot as I could reasonably get it, within the constraints imposed by defrost cycling, so run the ASHP flow at 40 deg C.  I've found that the old-style remote sensor type TMV that was fitted to our Wunda manifold is extremely good at regulating the flow down to about 23 to 24 deg C, below that and it starts to have problems regulating, though.

[Nickfromwales]

27 minutes ago, ragg987 said:

No blending required. The ASHP regulates the flow temperature. I have a 90l buffer to reduce cycling.

Ok, so ASHP > buffer then buffer > pump > manifolds? 

[ragg987]

34 minutes ago, Nickfromwales said:

Ok, so ASHP > buffer then buffer > pump > manifolds? 

Yes. So no blending at all in the chain on the basis that keeping the flow at the lowest setting gives best ASHP efficiency.

 

While I have implemented this successfully, I have yet to prove that flow temp is proportional to efficiency. @JSHarris has measured his and suggests that COP remains the same as flow temp rises (I cannot recall the range of flow temperatures he quoted - something around 30C). I recently addded a power meter to the ASHP so am now able to monitor - once the heating period starts.

[ragg987]

52 minutes ago, JSHarris said:

What's the minimum flow temp of the ASHP?  Mine just won't regulate at all below about 30 deg, and even then it jumps up and down by 3 or 4 degrees.  If the flow temperature to the UFH exceeds about 24 deg C then we get big temperature over-shoots in the house, even with room thermostats with 0.1 deg switching hysteresis, so I have to make sure that the TMV can accurately hold the flow manifold temperature at the relatively low set point.  This was one of the hardest parts to get right, getting really tight control of the UFH flow temperature, and realising it's significance in house temperature stability control.

 

I also use the buffer to preheat the DHW, so wanted that as hot as I could reasonably get it, within the constraints imposed by defrost cycling, so run the ASHP flow at 40 deg C.  I've found that the old-style remote sensor type TMV that was fitted to our Wunda manifold is extremely good at regulating the flow down to about 23 to 24 deg C, below that and it starts to have problems regulating, though.

Our Hitachi can regulate flow to any setting (through compensation control and heat curves - I saw it regulate between 23 and 30 last winter), though I guess if it is too low and there is insufficient demand in the slab that could lead to a lot of cycling given that minimum modulation is 30%. The buffer should help.

 

I also use the buffer to preheat incoming cold water into the whole house (apart from kitchen). My plumber rolled his eyes at the idea, but after he plumbed it in said it was a great idea and why didn't all houses have it. So preheat is limited by heating flow temperature - typically about 25-28C, though as it goes through a coil then the impact of preheat is limited to perhaps 20 to 25C.

 

I intend to create a post about our design at some point, but did not want to jump the gun and intend to run it for at least 1 year so I can comment on the reality.

[Nickfromwales]

10 minutes ago, ragg987 said:

Yes. So no blending at all in the chain on the basis that keeping the flow at the lowest setting gives best ASHP efficiency.

 

While I have implemented this successfully, I have yet to prove that flow temp is proportional to efficiency. @JSHarris has measured his and suggests that COP remains the same as flow temp rises (I cannot recall the range of flow temperatures he quoted - something around 30C). I recently addded a power meter to the ASHP so am now able to monitor - once the heating period starts.

Ok, so assuming the lower SET temp of the HP has little or inconsequential hysteresis, which is the bit I'm struggling with here, it does seem a simplified solution at a glance.

The only thing that would stop me from doing this for a 3rd party ( customer ) would be that there is no secondary safety net as the system is wholly reliant on the controller for the ASHP maintaining the low flow temp. If that ever throws a fit, then you could have excessively hot water allowed to feed into the floors, uncontrolled, which could cause damage to the floors. 

Its fine for homeowners to concoct their own solutions, but as an installer I absolutely must put in the required safety measures and failsafes or foot the bill ( or get sued or prosecuted ) if I don't.

My stance is maintained, I'm not a fan of this design, sorry.

FUI, A blending valve is a few £10's and would give you the failsafe, simply fitted before the pump  . 

[MikeSharp01]

4 minutes ago, Nickfromwales said:

FUI, A blending valve is a few £10's and would give you the failsafe, simply fitted before the pump

Perhaps an alternative would be a thermostat on the incoming pipe which switched off the ASHP if the flow temp gets too high. 

[ragg987]

1 minute ago, Nickfromwales said:

My stance is maintained, I'm not a fan of this design, sorry.

I respect this and am just offering a counterpoint. You probably forget more about plumbing and heating every day than I will ever know !

 

As a FYI, the ASHP design I have was approved by Hitachi and falls in line with their installation handbook. Your point about failsafe may be valid, perhaps the black-box that is the ASHP already has something built in I do not know. Certainly there is a setting in there that allows me to set the maximum flow temperature, however I am fully reliant on the integrity of the controller.

[Jeremy Harris]

My experience is that our Carrier ASHP just cannot hold the flow temperature anywhere near a constant temperature, even with a 70 litre buffer.  30 deg C is way too hot for the UFH, even in really cold weather I can't let the UFH flow exceed about 25 deg C, or else the house temperature will over-shoot for the next couple of hours or more, often by up to a couple of deg C, which is pretty uncomfortable.

 

I had to play around to get the TMV to regulate tightly at around 23 to 24 deg C, and even at 24 deg C UFH flow we get a bit of overshoot on the house set temperature, maybe as much as a degree. 

 

If I set the ASHP flow temp down to, say, 25 deg C, then what happens is that it drops to around 22 deg C, then rises to around 28 deg C or so, then drops back down to the lower temperature again, as it cycles on and off.  A 70 litre buffer, plus the concrete slab, just cannot absorb even the lowest modulated heat output from the ASHP at this very low flow temperature, so it cycles.

 

Running the buffer at 40 deg C and using an accurate TMV is a 100% fix for this, as the very much greater heat output power needed to get the buffer up to 40 deg C means that the ASHP can run at a low modulation level for a modest period, then just shut down for a long time, typically 24 to 48 hours, before firing up again.

 

I spent a long time playing around with different control strategies, including a lot of time trying to use slab temperature feedback as a control method, before finally settling on the system we have now.

Edited September 30, 2017 by JSHarris

[Nickfromwales]

9 minutes ago, MikeSharp01 said:

Perhaps an alternative would be a thermostat on the incoming pipe which switched off the ASHP if the flow temp gets too high. 

Still reliant on the HP controls . 

[ragg987]

11 minutes ago, JSHarris said:

I had to play around to get the TMV to regulate tightly at around 23 to 24 deg C, and even at 24 deg C UFH flow we get a bit of overshoot on the house set temperature, maybe as much as a degree.

You just reminded me - another reason I wanted to avoid a TMV is that it would be a single fixed flow temp setting. So if I set it for coldest day then on a milder day flow temp would be too high and system would have to cycle on and off or room temp would overshoot. Again, I am describing the theory as I understood it at the time but have learnt quite a bit about our system and the behaviour since then. At the moment I am fully at the mercy of the ASHP controller logic (which I quite like in reality - why reinvent the logic if a large company with millions to spend on R&D has already done it?).

[Nickfromwales]

12 minutes ago, ragg987 said:

I respect this and am just offering a counterpoint. You probably forget more about plumbing and heating every day than I will ever know !

 

As a FYI, the ASHP design I have was approved by Hitachi and falls in line with their installation handbook. Your point about failsafe may be valid, perhaps the black-box that is the ASHP already has something built in I do not know. Certainly there is a setting in there that allows me to set the maximum flow temperature, however I am fully reliant on the integrity of the controller.

Agreed, but it is a design in its barest, crudest form imo. Hitachi are probably unaware of the potential for overshoot in a PH and it also removes a heck of a lot of low cost energy for DHW preheat as you cannot define the two temp zones ( the temp of the buffer and the temp of the UFH flow ). 

If you simply add a cheap TMV prior to the secondary pump you'll be able to store the buffer at 40oC, which will provide a much better preheat temp and virtually wipe out any low flow hysteresis and cycling caused by running 'direct'. This will see the HP ramping up to 55oC less often and save on the electricity required to otherwise provide DHW. 

I think this simple tweak would give you a better performing system and a decent long term return. ?

 

PS, I'm here to pick up advice too, and am trying to forget the way I used to think and undertake jobs. This place is a goldmine of irreplaceable, invaluable and impartial knowledge. ?