ASHP Issues Leak & Buffer Tank with Loxone Thermostat

[Carpe Diem]

Hi, 

I have an ongoing issue with the ASHP on a property I've built.

In summary, we have a passivhaus c.450sqm with an 8kw ASHP, underfloor heating throughout.

The ASHP was installed by Magna Renewables, and it's now got to the point that NICEIC have had to step in, and I'd like some independent advice as the installer hasn't resolved.

We have 3 main problems.
 

1.Soon after install the energy usage was really high. Much higher than estimated. He is blaming Loxone because we have thermostats in each room and his view is that if it is calling when a single room cools, it is short cycling. Fair enough, but his solution is to remove loxone and have a single thermostats for the entire ground floor and one for the first floor. This doesn't work for me as a solution as we want individual control. There is no buffer tank. There is a low loss header. My (uneducated) view is that buffer may help resolve the issue as it would stop a small top up demand causing the ASHP to run. We have a 300l tank for hot water.

Any thoughts?

 

2. Since the engineer last visit, we have to keep tipping by up the tank as the pressure drops. Takes about a week to go from 1.7bar to 0bar. He is saying he will put leak stop in the system as we can't see any sign of leaks. This is after I turned off the valves to the UFH and hot water return, which he was saying is where the leak most likely was. I turned them off because I was panicking we had a big leak in the UFH so I figured if I turned them off, and the pressure stopped dropping then this was the cause. But it carried on, so he has now accepted it is in their install (somebody else did the UFH and hot water in the house).

Will leak stop work? Where is the leak if we can't see it? Is leak stop a bodge?

all pipes are in ceiling and its been ongoing for over 6 months and no wet marks.

 

3. Every so often we have no hot water. When I check, the immersion heater is running like it is doing a legionella cycle but that's been turned off. The immersion says it is in but the tank keeps cooling. My suggestion is the element  isn't working but he says he has checked power and it's fine. Note "power"..... he hasn't checked the element is working.

anybody else seen this?

 

Thanks all!

[dpmiller]

2. have you checked the air pressure in the pressure vessel? Might someone have isolated the vessel? A problem here will cause the pressure to fluctuate unexpectedly

[JohnMo]

54 minutes ago, Carpe Diem said:

Fair enough, but his solution is to remove loxone and have a single thermostats for the entire ground floor and one for the first floor. This doesn't work for me as a solution as we want individual control. There is no buffer tank. There is a low loss header. My (uneducated) view is that buffer may help resolve the issue as it would stop a small top up demand causing the ASHP to run.

Low energy houses don't need thermostats in every room.  When I did our house, I also had a thermostat in every room - guess what, our energy usage was twice as high as expected. Why - short cycling. If you want a thermostats in every room, live with the bills. Heat pumps and third party control equals high bills. Best bet is to let the ASHP just self control, UFH also works best this way.  The other alternative is a 2-port buffer with hydraulic separation, this will need to about 70L minus the volume of you smallest zone.  You need to control buffer temperature, this should be the only start stop permissive for the heat pump.  The heating side thermostats control a suitable circulation pump. This setup means only the flow that has to travel though the buffer does so, not all of it, allowing flow temp to be close to what you need.  But your bills will still be higher than no buffer and no zones.

 

I would and have, got rid of all the thermostats, manifold pumps and mixer, all zone valves, buffer, volumisers etc. - certainly in a Passivhaus there is zero need - we now now have none, ASHP is well happy, the floor is self modulating and the heat pump responds well to a need to heat or cool. Cooling at the moment, if the house is hot the heat pump senses this via the return temp and ramps up and runs longer, overnight the ASHP does next to nothing, as no need. Energy consumption, next to nothing at the moment doing cooling.

 

Drive everything direct from ASHP. Just balance the flows to rooms to get temperatures correct and set the WC curve, which should be almost flat. Ours starts at 10 (26) and goes down to -9 (29) - changes by 3 degrees 

 

Cylinder heating -

Do you have the heat pump set to heat DHW cylinder?

Some heat pumps (mine does) work in the following manner. You set the cylinder temp, if the heat pump doesn't achieve the heating in a single cycle it record where it got too and only heats to that level every other time. So example, you set to 55, the heat pump gets to 60 degree flow temp, if it has only achieved 45, it will only heat to 45 then after. So that's one thing to check.

To check immersion turn your immersion on - Cylinder should increase in temp if it works - leave for 1/2 an hour. If you have a smart meter the electric consumption should jump by 3kW if it does work.

 

Leak check, he should be able to pressurise the system with a hand pump to very high pressures to find the leak. Leak stop say no, say fix.

 

[JohnMo]

2 minutes ago, dpmiller said:

2. have you checked the air pressure in the pressure vessel? Might someone have isolated the vessel? A problem here will cause the pressure to fluctuate unexpectedly

We had a similar issue on a gas boiler, the diaphragm had a hole in it, new vessel issue went away

[Conor]

1. Get rid of all the stats and run each floor as a zone. You might have spent money on wireless stats etc, but it's really not needed. A buffer won't really help, as you'll be spending more energy heating it up than the space, and you'll still get multiple short cycling issues.

2. Leak is likely to be a faulty relief valve or expansion vessel or anti freeze valve.

3. If the element is blown the circuit will be broken and you will see this as no power will be flowing. Regardless, your ASHP should be doing the heating so would look there first.

[Kelvin]

I really couldn’t see the advantage of connecting the ASHP to our Loxone system. Just looked to be adding extra complexity. 

[jack]

1 hour ago, Carpe Diem said:

In summary, we have a passivhaus c.450sqm with an 8kw ASHP, underfloor heating throughout.

 

He is blaming Loxone because we have thermostats in each room and his view is that if it is calling when a single room cools, it is short cycling. Fair enough, but his solution is to remove loxone and have a single thermostats for the entire ground floor and one for the first floor. This doesn't work for me as a solution as we want individual control.

 

Individual control - in the sense of tightly controlling individual room temperatures - doesn't really work in a passivhaus with underfloor heating. Most of us (me included) on here with a similar setup treat the whole floor as a single zone and run with all loops open at all times. You can adjust flow rates to individual rooms at the manifold so that they get relatively more or less heat than the others.

 

Do you know how the call for heat has been set up with Loxone? The worst way to do it would be to have a simple OR gate, such that any zone can call for heat. Much better would be something like at least two or even three zones calling for heat before triggering a call. Alternatively, or in addition, you could work in some averaging. You can also do more complex stuff like weather compensation (if you have an input for the external temperature).

 

Loxone is insanely powerful for this sort of thing (edited to add:), although I wouldn't suggest that anyone design a system in this way. I'm suggesting it only because you've already paid for and installed all the necessary hardware.