Ground source heat pump - temp monitoring

Sustainable Energy
1

I’ve had a ground source heat pump for several years and have been measuring the electrical power. I want to start measuring temperatures to better understand its efficiency.
Which lines should I add DS18B20s to?
My options are —

  • water/methanol supply line from my yard
  • water/methanol discharge line from my yard
  • freon line to my heating/cooling coil in the air handler
  • freon line from my heating/cooling coil in the air handler

PS: I also —
measure power used by my air handler.
measure the electric power used by my AUX electric heating coil.
I also use superheat to warm my domestic hot water before going into the primary hot water heating tank, but wonder if I should monitor anything here?

P.

2

Without wanting to sound flippant, if you can, measure everything.
That way you’ll have a better handle of what’s going on.
Decent DS18B20 sensors are a couple of quid each, a Pi/EmonTH/ESP8266 isn’t too much either.
I assume you have a working EmonCMS setup?

3

Thanks. I will do that.
Question: what do I do with data?

4

Stuff it all into EmonCMS. Then draw some graphs.
Then overlay different ‘chunks’ of data and see how things interact. Like external vs internal temperatures, vs energy use, vs HP runtimes/cycling.
With a few months (or even years of data) patterns may start to emerge.

5

Continuing the discussion from Ground source heat pump - temp monitoring:

Some time has passed while I got some measuring gear installed on my GHP.
I am measuring the methanol/water mixture temperature as it comes from my ground loops and after it exits the heat pump.
I have 6 ground loops and 2 compressors. It’s about 6 tons or 6.3kW of capacity.
I monitor the W drawn by the pump and compressors.
I have not installed a heat meter mainly because it’s $$ and I’d rather not break the lines open and thereby entrap air.
I have the pump curve showing head pressure vs flow rate for the size impeller I have.
Installed a pressure gage, not a transducer, yet. I read about 3 psi, which is equivalent to about 36 gpm. Or 6 gpm per ton or 6pm per ground loop. It’s on the high side, but that’s ok. Run well and silent.

Next step is to fill in the feeds for the COP heat pump app.

Since I know the flow rate, the water/alcohol mixture and specific heat, can I use these as input to the COP App?
If so, I’m lost as to how!!!

6

Look at this post by @Zarch although I’m not sure how to add that to the app :slight_smile:

7

The heat pump app takes the following inputs

image
image350×682 9.53 KB

ie, it expects the heat meter to provide the heat output.
The heat meter is doing the following calc under the hood for us.

Heat Output = Specific heat capacity x flow rate (l/s) x (flow temperature - return temperature)

So if you have those raw figures available to you, perhaps you can create your own ‘heat output feed’ based on the inputs you have?

8

You need to add in density for the methanol mixture (Mick is using water only in his system I think): Design of a central heating pump with example calculation has a nice worked example.

If the density and SH are relatively constant across your operating conditions (dT) then it looks like you should have enough info to process some inputs into a feed suitable for the heat pump app.

9

Yep, i’m water only.

From the Heat Geek materials I’ve seen,

Specific heat capacity (SHC) of water is 4.2 and it’s 3.8 for Gylcol.

There might be more complex ways of working that all out, but those are the figures I’ve been passing on.

10

(eg Sentinel R600)

11

Hey, thanks for jumping on with the replies. Super helpful.
Here’s what I found for a 50:50 MeOH:H20
Specific heat = 3.437 [kJ/kg-K] or [J/g-C] from Table 8-3-2
Density 0.92606 g/ml @ 4 degC from Density and Concentration Calculator for Mixtures of Methanol and Water
Flow Rate of 36 rpm = 2.2712 Liters per second
Delta T is 1.2 deg C.
Using from above:
Heat Output = Specific heat capacity x flow rate (l/s) x (flow temperature - return temperature) * Specific gravity
Heat output = 8,674.72 (J/sec) or W or 8.674 kW

Thanks all for the help!

I’ll create a feed using these data and see what happens!

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