Heat pump testing issues

[robb1303]

Hello all, nice forum you have here.

Hopefully some of you will be able to share some of your experience in helping me with a problem I am having.

Without initially going into too much detail I am trying to build myself an airsource heatpump to provide heating water requirements for a low temperature under floor system I plan on installing.

Now I have been learning about refrigeration as I go with my project, so am by no means an expert, however I come from an engineering background and consider myself to be fairly competent.

What I have put together so far has a LG BLDC compressor driven by an inverter, solenoid controlled expansion which I am controlling with a cruzet timer(for now), evaporator and condenser I would consider to be suitably sized, refrigerant is R410a. For the process of testing this unit is currently connected to 3no 3Kw fan convectors to reject the heat to the outside.

I have fired the unit up and had a bit of a play manually with the settings and it was running well initially at 6degC evaporating, 40degC condensing, this was giving me about 4degC of superheat and 7degC of sub cooling.

I was happy with this until I noticed my problem, by using water out and return temperatures and flow rate of water I calculated that it was only giving out 2.5Kw to the convectors. From the compressor spec sheet at the conditions where I was operating the compressors should have been giving me 4.8KW, I also noticed that it should of been using 1.1KW and drawing 7.22A yet my unit was displaying 516W and 4.3A, so you can see I am a long way down on power yet also drawing less power than I should, any reasons why this would be happening?

I thought maby the inverter wasn't supplying the correct frequency to the compressor but when I checked it with an oscilloscope it was fine, I read somewhere on line this it might be a blockage in the suction line, don't know if this is something I need to check?

Refrigerant level?

Really has stumped me a bit this one so hopefully some of you can help?

Sorry for the long first post.

[Brian_UK]

You say that you have "solenoid controlled expansion which I am controlling with a cruzet timer".

Could you please explain this a little more? Normal expansion is either a capillary line or an expansion valve.

Also, being a bit of a pedant, do you have a Refrigerant Safe Handling ticket to be working on this?

[robb1303]

Fixed it now, I was being a bit thick the motor in the compressor is a 4-pole motor thus the frequency on the inverter display need to be doubled to operate at the correct speed. Makes sense that everything was down by half.