Which pocket for the temperature probes in the Unvented cylinder (UVC)

[MikeSharp01]

Almost complete on the HP install all flushed through, pressure tested everywhere and filled for testing (still need the inhibitor)  Powerup tomorrow, would have been yesterday but weather stopped us because you have to take the lid off the HP to make the final electrical connections if you want a BMS connection.

 

Anyway the final challenge is to fit the temperature probes into one or both of the pockets in the UVC. There are two pockets one at about 50% height and one at 75% height and there are two probes. One (A) looks after the immersion heater and the other  (B) looks after the Heat Pump - sends Domestic Hot Water (DHW) data direct to the HP presumably for the HP to know it has got the water to the required set point. The tank is quite dumpy and 200l so I assume it makes no difference as the tank probably does not stratify so well that it matters. Have I go that right? To help me out I have used the top pocket for both so if it does stratify I am working on the hottest water and I can read the temperature from the BMS and its reading the same temp as the immersion limits.

[John Carroll]

If you are talking about a Immersion then presumably its a Electrical Immersion, if so, the UVC will have somewhere to install this, these immersions have their own integral stats and measure the water temperature where ever they are installed, THe 50%& %75% probes should determine what vol of hot water  is used before the HP or boiler is called on to start reheating, HPs might tend to have the probe at 50%, if measuring from the bottom up then the HP might use the 75% pocket.

Edited 23 hours ago by John Carroll

[ProDave]

The tank WILL stratify.  Not so much when it is being heated, but as you draw hot water it exits at the top and is replaced by cold water entering at the bottom.  Those don't mix much so the hot / cold transition just moves up the tank.

 

So you want the heat pump probe, the one the heat pump used to measure temperature in the lowest pocket available, so it detects the cold water as soon as possible and starts re heating.

 

I initially tried mine in a higher pocket, and the tank did not re start heating until half the hot water had been consumed.

 

The immersion heater one?  Are you talking about the safety thermostat part of the cylinders safety system?  I have that in the higher pocket.  this is the one that is supposed to shut down the heating demand and close the motorised valve to protect from a runaway out of control heat source.

[SimonD]

3 hours ago, MikeSharp01 said:

UVC

 

What UVC have you got? I'd usually expect the pocket for the dhw thermostat to be about 1/3 way up. Can we have photos?

[MikeSharp01]

3 hours ago, ProDave said:

The immersion heater one?  Are you talking about the safety thermostat part of the cylinders safety system?  I have that in the higher pocket.  this is the one that is supposed to shut down the heating demand and close the motorised valve to protect from a runaway out of control heat source.

Yes the safety stat but as it's a heat pump it cannot reach dangerous temperatures so I have assumed that I don't need it for that, is that not OK, and have put it into the immersion circuit as described here: 

and you commented on at the time.

 

2 hours ago, SimonD said:

What UVC have you got? I'd usually expect the pocket for the dhw thermostat to be about 1/3 way up. Can we have photos?

It's a Telford Tempest Heat Pump cylinder and the two pockets are shown in the image below, which was taken as we worked out the pipe runs, hope it is enough but I can get a full picture tomorrow - not quite sure why I don't have one already. There is nothing low down only the two showing.

[ProDave]

47 minutes ago, MikeSharp01 said:

Yes the safety stat but as it's a heat pump it cannot reach dangerous temperatures so I have assumed that I don't need it for that, is that not OK, and have put it into the immersion circuit as described here: 

DO fit the safety thermostat.  What if the HP has an immersion built in that it uses as backup?  many do?  What if you have an immersion in the tank itself?

[MikeSharp01]

9 minutes ago, ProDave said:

DO fit the safety thermostat. 

Yes I have, via the contactor route I discussed. I am not sure if the Heat Pump has a boost heater I will check that but whatever happens I don't want that heat getting round the UFH so control of three way valve won't happen but I could just kill the power to HP I suppose using the same signal.  

[SimonD]

1 hour ago, MikeSharp01 said:

It's a Telford Tempest Heat Pump cylinder and the two pockets are shown in the image below, which was taken as we worked out the pipe runs, hope it is enough but I can get a full picture tomorrow - not quite sure why I don't have one already. There is nothing low down only the two showing.

 

Ah, okay. On that specific model the lower 22mm thermostat pocket is 700mm from the bottom of the cylinder and the higher one 1000mm. Don't get these confused with the 22mm secondary return which is at 1220mm. Your heat pump sensor needs to be in the lower one. As the wiring diagram shows the wiring in of an over-temp cut out and control, you should follow that diagram. Some manufacturer's like Viessmann on gas boilers for example, don't require it on a 4-pipe system as the safety cutout is built into the boiler itself (yes, I know yours is a heat pump but it's included in the schematic).

 

 

Data sheet attached:

 

TEMPEST HEAT PUMP DATASHEET -.pdf

 

 

[MikeSharp01]

1 hour ago, SimonD said:

Your heat pump sensor needs to be in the lower one. As the wiring diagram shows the wiring in of an over-temp cut out and control, you should follow that diagram. Some manufacturer's like Viessmann on gas boilers for example, don't require it on a 4-pipe system as the safety cutout is built into the boiler itself (yes, I know yours is a heat pump but it's included in the schematic).

Which schematic are you referring to. The only one I have is in the manual and looks to refer, as you say to a boiler based system. (Link: https://www.telford-group.com/download.php?file=VG9ybiBUZW1wIEluc3RhbGwgR3VpZGUgMjAyMy0yNDUucGRm)

 

It does say controls provided must be used but I obviously cannot use the above circuits as I don't have; the programmer - that's in the heat pump, the three way valve operation - that's controlled by the heat pump, the pump - that's in the heat pump so I just used the dual stat to limit the immersion. The max output temperature of the heat pump is 75^oC so it should not need any boosting as legionella should be gone with 30 minutes at 60^oC.

 

I cannot see anything in the manual for the heat pump about an inbuilt booster heater but it does have provision for what is called additional heating (5A@240V) as an external connection. (See image below)

 

So I am using the dual stat to control the immersion (despite it being an intelligent one - which can do all kinds of things on its own. I could take the additional heating signal from the heat pump (terminal 1) and use that to drive, via an appropriate interface,  the call for immersion signal discussed in the thread above but as far as I can see the heat pump manual makes no reference to the use of that signal other than as part of the commissioning check list and nothing to say this additional heat source should be controlled by the additional heating signal.

 

 

 

 

 

[ProDave]

It is difficult to advice on heat pump wiring as each make is so different.

 

Mine, an LG controls the motorised valves which connect directly to the heat pump.  Mine has 3 terminals labelled "motorised valve" which actually turns out to be 2 outputs one for heating and one for hot water.  You could use a 3 port changeover valve, but I chose to use individual 2 port valves.

 

So I wired mine according to the heat pump wiring diagram.

 

Then that over heat thermostat on the cylinder.  That is a mechanical changeover contact thermostat.  So I just connected the normally closed contact in series with the feed to the hot water motorised valve.  So normally everything works as it should.  But if by chance the cylinder gets too hot, the thermostat would open, breaking the feed to the motorised valve and shutting off any flow of heating water into the cylinder.

[SimonD]

12 hours ago, MikeSharp01 said:

Which schematic are you referring to.

 Maybe my bad, as I briefly scanned the schematic linked in your previous thread and assumed it was part of the manufacturer's instructions where is has an over temp cut out (the black background schematic) - but perhaps this assumption is incorrect?

 

All unvented installations must have some kind of non-self resetting over temperature device. This doesn't have to be on the cylinder as it can be built into the heat source - i.e. G3 provides for alternatives such as Viessmann's boiler 4-pipe. Now, I know that your heat pump can only go to 75C so there is a reasonable assumption that you don't need this kind of device, but what I would suggest is that you put a call into the heat pump supplier and/or the company doing the commissioning and sign off to directly ask the question because there is nothing we can see that explicitly covers this in the heat pump's documentation. The UVC manufacturer will just supply the whole kit that complies with G3 and tell you that need everything, because that's what they're obliged to do.

 

Technically, the heat pump supplier and company doing the umbrella stuff shouldn't be letting you do the installation on your own and figuring all this out as you go without proper documentation and instructions, and may I suggest, some initial training. You should at the very least have a technical contact to guide you through it all, particularly as at the moment it seems to be overly complicated. Personally, I don't think this is very good at all from the company doing all the regulatory stuff for you.

 

 

Edited 3 hours ago by SimonD

[JohnMo]

Trouble I have answering this thread is the heat pump control is being somewhat taken over by another 24v system, so it's a can of worms. Simple made difficult.

[MikeSharp01]

2 hours ago, JohnMo said:

Trouble I have answering this thread is the heat pump control is being somewhat taken over by another 24v system, so it's a can of worms. Simple made difficult.

None of the heat pump functions are controlled by the 24V system only the immersion and the heat pump does not want to control that as far as I can see. I chose to put the dual stat into to the 24V side because the switches in the dual stat look flimsy, you cannot get a piece of flex capable of carrying the full current of the immersion into the gland provided in the dual stat box and I didn't really want high current switching on the tank. If it will help I can wire the dual stat into the immersion direct I just need to be creative with the gland problem.