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Practical advice on instrumenting Heatpump

  • 30-04-2008 2:08pm
    Registered Users Posts: 1,081 ✭✭✭ KAGY

    Hi all
    This is really a follow up to sinnerboys thread on field testing a heat pump. here

    Being an (ex) mechanical engineer and a geek to boot, i'd be very interested in instrumenting the bejasus out of my heatpump. I've a bit of experience in this from a Masters I did, but I'm out of the loop now and looking for some practical advice, such as the cheapest or parallel thinking solution. I spent about 10k easy on pressure gauges, flow meters, thermo-couples and DAQ for my masters, but I obviously am not going to spend anything near that.
    Basically I'd want to measure the COP (Elec in / Heat Out), the efficiency of the circuit (Glycol Heat in / Water Heat Out).
    • I'm getting a electrical check meter (kWhr) just for the heatpump and circ pumps.
    • Thermocouples on the flow and returns on both secondary circuits would be a given
    • Flow meters would be probably too pricey, do you think that measuring the current at the pumps would be adequate?
    • I'd like to measure the high / low pressure in the ref'n circuit, AFAIK 2 bordon gauges for refrigerant, plus the capillary tubes would run to €150. Is there a cheaper solution.
    • I like for all of this to be electronic, I've an old PC that I could dedicate to Data Aq. Any cheapish solutions out there?

    Any thoughts?


  • Registered Users Posts: 23 Gtec


    I started down this road for my solar installation because prior to buying it I could not find any hard data from Irish installations, just plenty of "sales" figures like 70% of hot water etc.

    Initially I have just put in 4 temp sensors and logged the results (live data available on

    For the system that is currently live I used a simple temp logger from Quasar electronics in the uk that uses DS1820 one wire temperature sensors. these are really nice as you do not have problems with cold junction comparisons.

    I am working on a mark II version which will be based on a custom data acquisition system using a PIC microcontroler, 10 temp sensors, 2 current sensors and a flow meter (for water usage these can be obtained from Radionics at a reasonable cost).

    Along the way I have looked at all sorts of DaQ systems, and I think if you don't want to go as far as writing your own microcontroler code, then the LabJack is one of the best devices on the market for interfacing sensors to a PC at "hobby" prices.

    Let us know how you get on, in my opinion installing any renewable type system without instrumentation and intelligent control is a complete waste of time!

    (In the interest of full disclosure the website linked above is a commercial site. The data is from my installation, but I have no commercial involvement with the owner of the site, simply a friend)

  • Registered Users Posts: 12,553 ✭✭✭✭ AckwelFoley

    Hi Getec, i looked at the results and its pretty interesting.

    How much do youthink it would cost "Joe Bloggs" to set up a system like this for solar?

    And what would be the advantage for setting up this temp graph after the fact? The results a householder need is.. is their tank hot or not..

    I dont know if its something that they would need.. i could be wrong of course..

    But certainly the figures are great as an example to show the different out puts through the seasons and then graph it on an annual basis.

  • Registered Users Posts: 23 Gtec

    Hi Snyper,

    the simplest way for "joe bloggs" to capture this kind of data would be to buy a solar controller and DaQ system from the get go, these are availble (I have seen the Resol one advertised at rvr) as far as I know these come with some sort of software for reviewing the data on a PC.

    To get it up and running on the web is a little more complicated, I'm not sure if there is comercially available software to do this easily.

    I agree that knowing the data after the event is not much use to the householder, the reason for the implementstion i did was to demonstrate the potential of solar for people considering buying it. My motivation for the MarkII design is partly interest, partly I would like to design a completly inteligent controller that learns my water usage paterns and ensures that HW is available when required, but uses the most economical method of heating it - e.g. use the boiler if it is on and the data shows the sun has gone off the panels for the night, otherwise use the imersion on "sink" setting 20 mins before the HW is required.... that sort of logic if you see what i mean.

    Fundementally what I am trying to achive is a system that provides me with HW whenever i need it, but does not use external energy to heat a tank of water that is then left to cool down again, a sort of artificial inteligence system for DHW - maybe I need to get out more ;);)