Brads Gas & Gear

BradC · 01-09-13, 11:24 PM

My new clamp meter arrived. Yay! Here's a quick brain dump after taking some measurements.

I have not got the flow meter properly calibrated yet (the vendor told me after I had received them that their calibration values were a best guess and had not been validated!) so my system heat output is a best guess with what I have available (evap air flow, relative humidity & temperature differences). The system power consumption hovers around 2KW. So that's ~1.4KW for the compressor, 350W for the evap fan, 200W for the water pump and the rest is control system and misc losses. I'm moving between 7000 & 8000W of heat, so my entire system COP is at worst 3.5 and at best 4.0. I throttled the HX back to get a condensation temperature approaching 50C and gained 700W of system power consumption.

I've check some spec sheets for new Daikin and Fujitsu inverter systems, and the best they spec for COP is 3.4 for a 5KW unit and 3.28 for bigger unit. Calculating it out based on their detailed specifications, the COP they are specifying is for the compressor condenser units and does not appear to take into account the evap head.

So, while I've spent more on the total system enhancements than I'll ever recover in power cost, I've still spent less than the cost of a new ducted inverter unit *and* I'm using less power.

Now, none of this is optimised yet. The EEV is being "hand" controlled at the moment, the injection bore has ~7PSI of back pressure and I'm losing 25KPA of pressure between my suction service valve and the suction port on the compressor (~1.5K of temperature). It looks like this accumulator/reversing valve/compressor combination is at its flow limits. Hardly surprising given it was moving about 6KW of heat into a condenser at ~60C and it's now moving over 7KW of heat into a condenser at ~25C.

Apparently this is common knowledge, but it's new to me : As you unload a single phase motor the power factor progressively gets worse, so while you are using less Watts your overall VA draw drops very little. I should remedy that with my next compressor condenser unit where I have a three phase compressor on a VSD. This will maintain a very good power factor under varying load conditions and allow me to trim the compressor capacity to suit the system heat load better.

01-09-13, 11:24 PM	#33
BradC Apprentice EcoRenovator Join Date: Dec 2010 Location: Western Australia Posts: 148 Thanks: 1 Thanked 48 Times in 34 Posts	My new clamp meter arrived. Yay! Here's a quick brain dump after taking some measurements. I have not got the flow meter properly calibrated yet (the vendor told me after I had received them that their calibration values were a best guess and had not been validated!) so my system heat output is a best guess with what I have available (evap air flow, relative humidity & temperature differences). The system power consumption hovers around 2KW. So that's ~1.4KW for the compressor, 350W for the evap fan, 200W for the water pump and the rest is control system and misc losses. I'm moving between 7000 & 8000W of heat, so my entire system COP is at worst 3.5 and at best 4.0. I throttled the HX back to get a condensation temperature approaching 50C and gained 700W of system power consumption. I've check some spec sheets for new Daikin and Fujitsu inverter systems, and the best they spec for COP is 3.4 for a 5KW unit and 3.28 for bigger unit. Calculating it out based on their detailed specifications, the COP they are specifying is for the compressor condenser units and does not appear to take into account the evap head. So, while I've spent more on the total system enhancements than I'll ever recover in power cost, I've still spent less than the cost of a new ducted inverter unit and I'm using less power. Now, none of this is optimised yet. The EEV is being "hand" controlled at the moment, the injection bore has ~7PSI of back pressure and I'm losing 25KPA of pressure between my suction service valve and the suction port on the compressor (~1.5K of temperature). It looks like this accumulator/reversing valve/compressor combination is at its flow limits. Hardly surprising given it was moving about 6KW of heat into a condenser at ~60C and it's now moving over 7KW of heat into a condenser at ~25C. Apparently this is common knowledge, but it's new to me : As you unload a single phase motor the power factor progressively gets worse, so while you are using less Watts your overall VA draw drops very little. I should remedy that with my next compressor condenser unit where I have a three phase compressor on a VSD. This will maintain a very good power factor under varying load conditions and allow me to trim the compressor capacity to suit the system heat load better.