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 6 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