Renewable Heating Hub Heat Pump Forums

Search with Wattson
Forums
Renewable Heating
Air Source Heat Pum...
Why are my flow and...
 
Notifications
Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

Why are my flow and return temperatures reading the same?

 
Page 2 / 2
Air Source Heat Pumps (ASHPs)
Last Post by Bob77 2 years ago
14 Posts
3 Users
1 Reactions
9,641 Views
RSS
 iancalderbank
(@iancalderbank)
Prominent Member Contributor
Joined: 4 years ago
Posts: 643
22/11/2023 3:20 pm  

so the most likely explanation is that there is another circulating pump in your system, and you also have a buffer tank or low loss header (LLH) in your system. 

the other pump will either be in the outdoor unit or near to the buffer tank / LLH, on the heat pump side of the piping. that's what's called the primary pump - its responsible for the flow rate you are seeing. the temperature sensors you are seeing are those of the primary flow and return, in / out of  the heat pump.

when your system is in CH mode, the HP supplies warm water to top the buffer tank(or LLH), that water being moved by the primary side circulation pump. and it takes cool(er) water from the bottom of the buffer tank. The UFH takes warmer water fromt he top, uses it to heat the house, and puts it back into the bottom. That called the secondary side. Thus there are two separate circulating loops that join in the middle.

when your system goes into HW mode it'll switch a valve for the water flow so that instead of going from the HP into the LLH, it goes direct to the cylinder. So in that case, the flow rate, and flow/return temps, that you see , are those of water flow directly between cylinder and HP. So the HP is seeing the true DT and flow rate of the cylinder.

But in CH mode, your HP doesn't "see" the heating system. It simply "sees" a buffer/LLH that keeps on losing some heat, and keeps topping it up.

Note in CH mode via the buffer/LLH, that the flow rates of the two loops are completely separate, and if the flow rates differ significantly then the DT will also. Read this about how a system with LLH/buffers works (HeatGeek is always a good place to start) . 

 

edit - I missed your info in previous posts. seems like you have an indoor unit with a PHE (Plate Heat Exchanger) and a separate primary side pump. The PHE is doing similar job to LLH as I mentioned above, separating the two sides. your temperature readings and flow rate that your system reports will still be on the primary side, you will never see the UFH side DT or flow rate without additional sensors.


My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs


   
👍
1
ReplyQuote
 Bob77
(@bob77)
Trusted Member Member
Joined: 3 years ago
Posts: 36
Topic starter 28/11/2023 1:09 pm  

@iancalderbank Thanks Ian for that explanation.

I have noticed that in recent days with colder weather and a higher LWT temperature, there is more of a difference between leaving and returning water temperatures. Anyway the house is warm and the electricity consumption has been reasonable, so that's really all that matters!



   
ReplyQuote
Page 2 / 2
Forum Jump:
  Previous Topic
Next Topic  
Share:

Join Us!

Latest Posts

Click to access the login or register cheese
Protected By
Shield Security PRO