TiredGeek
23-02-2011, 07:34 PM
Guys, I'm having problems with my ASHP's icing up, and I'm wondering if I've set the clever room stat properly to work with ASHP.
The room stat is a Honeywell CM900 Programmable Room Thermostat
There are a few settings I'm not sure about: Proportional band width, minimum on time, cycle rate, optimisation.
I have set the thing to the recommended settings for Heat Pump, which is minimum on time = 4 mins & cycles per hour = 3
A "consultant" has suggested the Honeywell maybe causing the ASHP to cycle on and off and leading to issues with icing, or even turning them off part way through the defrost cycle.
I wonder if it's because the thing is so accurate it's turning the units on and off too often before they've had much of a chance to warm the water enough for them to use it to do a defrost. I'm wondering if there's a way to "desensitise" it from it's current 0.5'c accuracy.
The problem only happens when the house is unoccupied and the stat is set to 10'c.
I don't understand what "Proportional Band Width" does as there is no explanation in the manual. Maybe that's what I'm looking for?
"Optimisation" turns the heating on early if it thinks the room temp won't make it to the set target in time. So say it's set for 12'c overnight 'till 6am then 18'c at 6.10am, it will turn the heating on at 5.45 to start to build up the heat to meet the target at 6.10.... I think.
Frankly everyone is scratching their heads at the moment over the cause of the icing so I wonder if there is a better setting for the room stat and if that will help.
The room stat is a Honeywell CM900 Programmable Room Thermostat
There are a few settings I'm not sure about: Proportional band width, minimum on time, cycle rate, optimisation.
I have set the thing to the recommended settings for Heat Pump, which is minimum on time = 4 mins & cycles per hour = 3
A "consultant" has suggested the Honeywell maybe causing the ASHP to cycle on and off and leading to issues with icing, or even turning them off part way through the defrost cycle.
I wonder if it's because the thing is so accurate it's turning the units on and off too often before they've had much of a chance to warm the water enough for them to use it to do a defrost. I'm wondering if there's a way to "desensitise" it from it's current 0.5'c accuracy.
The problem only happens when the house is unoccupied and the stat is set to 10'c.
I don't understand what "Proportional Band Width" does as there is no explanation in the manual. Maybe that's what I'm looking for?
"Optimisation" turns the heating on early if it thinks the room temp won't make it to the set target in time. So say it's set for 12'c overnight 'till 6am then 18'c at 6.10am, it will turn the heating on at 5.45 to start to build up the heat to meet the target at 6.10.... I think.
Frankly everyone is scratching their heads at the moment over the cause of the icing so I wonder if there is a better setting for the room stat and if that will help.