Wow, it's been one year to the day.. It's a LOT colder here this year..
(See the temp chart above from 12/17/2012).


http://ecorenovator.org/forum/attach...1&d=1387300378

One of my Sanyos did a defrost cycle this morning, but the dew-point wasn't that bad..?.
When it got above 13F, I tried to increase the setpoint (room temp) from 20C to 21C..
But, it was still too cold for living room Sanyo. Too much load and it reset.
I went out and checked, there wasn't any ice..

Maybe the controller's frost detection function can be tricked when the
outdoor temp gets close to the bottom end of it's operational range.




I'm still thinking about building an ice detector, using the TCRT5000 optical gizmo I tested last winter.. :o

Xringer, What is the lowest outdoor temp you have measured and what kind of performance have you seen with your HPs?

My outdoor sensor averaged around 7F this morning for a few hours.

The local Underground weather station (1/2 mile from here) showed colder..
Today's Extremes
High Temperature 14.8°F 1:10pm
Low Temperature -2.2°F 7:34am

I left the Sanyos set to 20C overnight and they did good all night.
We were up before 6AM and the temp was still dropping.
Lowest temp indoors was 19C, when I was playing with the set point..
I should have left it at 21C overnight and I think it would have worked better.
Maybe we could have avoided re-starts when trying to jump up 1deg C..


I think the average temp since midnight has been about 8F! :eek:
As of 13:20, we've used 24.1 kWh.. ($4.10)..
About 1.826 kW every hour since midnight.. 913 watts used by each unit.


http://ecorenovator.org/forum/attach...1&d=1387304517

This was the coldest night I've seen in years!!
Right now, it's 16F and there is snow piling up out there for me to shovel.. :eek:

Great to hear from you again Nigel, and thanks for your good analysis.

I don't know if it will help your defrost project here, but I have noticed that in the cheap de-humidifiers I have disemboweled, there is a thermistor pounted to a small flat plastic mount that is inserted so that the plastic goes between the fins of the evaporator, leaving the thermistor just above the fins. The thermistor is positioned on the air-in side of the evaporator, in the fin area, close to the area that frosts up. It is not at the area where frost would first occur, but a bit further out. The de-humidifiers I have looked at rely on the evaporator coils frosting up, and the subsequent defrost cycle to melt, capture and contain the humidity that is being removed from the air.

I have wondered what temperature the thermistor sees... must be the freezing point of water. This would work in an interior where there was certainty that the machine wouldn't be used in freezing weather. You likely couldn't count on this for your heat pump.

Perhaps you could use this idea to sense the presence of actual frost to trigger the defrost cycle.

Optical maybe?

IR maybe?

Physical probe maybe?

Maybe something that could detect the cessation of airflow through the most likely part of the evaporator to frost up?

Best,

-AC

hi Acuario I think that you should check this page for defrost algoritm if you have not solved it yet
harizanov.com/2012/02/defrost/
basically he incorporates an outside humidity sensor and changes the time cycle for defrost based on relative humidity.
so his plan is to:

No defrost above +5 degrees C

Default time between defrosts (Td) is 45 minutes of accumulated heat pump work time.

If air humidity is <65% then increase time between defrosts by 135 min
If air humidity is between 65% and 75% then increase time between defrosts by 90 min
If air humidity is between 75% and 87% then increase time between defrosts by 45 min
If air humidity is between 87% and 99% then increase time between defrosts by 0 min and BREAK further processing (humidity too high to risk defrost delays)

If outside temperature is between 6 and -4 then increase time between defrosts by 0 min
If outside temperature is between -4 and -7 then increase time between defrosts by 45 min
If outside temperature is between -7 and -99 ,increase time between defrosts by 90 min

I'm still playing with improving the defrost efficiency.
I'm currently testing out a pressure differential system.
http://ecorenovator.org/forum/geothe...heatpumps.html