Heatpump defrost cycles determined by ...?

[boaterbob]

Living in SC and using a heat pump, I have the heat setpoint at 69 degrees. With night temps around 50 to 55 degrees it seems the heatpump runs most of the night. From the sounds of the heatpump it seems the defrost function makes up a lot of the runtime. A HVAC tech said my defrost cycle is probably set to 3 times an hour.

My question - does the defrost cycle depend on outside temp or on how many times it is set for regardless of the outside temp. For example, if the t-stat setpoint is 69 degrees and the outside temp is 20 degrees I could see the need for the defrost cycle to run more frequently but what if the setpoint is still 69 degrees and the outside temp is 60 degrees, why would I want the defrost cycle to run 3 times an hour. It seems that just by having the t-stat in 'Heat' mode that the defrost cycle works without any consideration of the outside temp. Having the defrost cycle run so often with mild outside temps just seems to be a waste of electricity.

Robert

[rlj1117]

i would have someone out that knows defrost cycle, depends on brand as to what forces defrost, what area in sc?

[re2ell]

Originally posted by boaterbob
Living in SC and using a heat pump, I have the heat setpoint at 69 degrees. With night temps around 50 to 55 degrees it seems the heatpump runs most of the night. From the sounds of the heatpump it seems the defrost function makes up a lot of the runtime. A HVAC tech said my defrost cycle is probably set to 3 times an hour.

My question - does the defrost cycle depend on outside temp or on how many times it is set for regardless of the outside temp. For example, if the t-stat setpoint is 69 degrees and the outside temp is 20 degrees I could see the need for the defrost cycle to run more frequently but what if the setpoint is still 69 degrees and the outside temp is 60 degrees, why would I want the defrost cycle to run 3 times an hour. It seems that just by having the t-stat in 'Heat' mode that the defrost cycle works without any consideration of the outside temp. Having the defrost cycle run so often with mild outside temps just seems to be a waste of electricity.

Robert

Robert, without knowing what specific make of heat pump you have, i'd like to keep my response general of all heat pumps.

defrost initiation is usually controlled by cycles per time passage and temperature of the outdoor coil. generally, if no defrost is needed, (determined by the coil temp), then the time cycle will be over-riddened, and no defrost will initiate.

if your particular unit is defrosting that frequent, possibly could be very high humidity, and relativly warm outdoor ambient.

i agree with rlj, have your unit serviced to determine if the defrost control is working correctly.

[boaterbob]

In response to a posting: I have an approx 2100sf 3 year old home in Charleston, SC. The HVAC system outside unit is a Tappen FT3BA-036KA, 10 SEER (3 ton - discontinued unit). The thermostat is Honeywell T8400 very basic unit ( Fan - ON/AUTO , System - COOL/OFF/HEAT, with UP/DOWN temp buttons ). Outside temps have been around 50 each night with high outside humidity. During the day (Noon and on) the temps are around 73 degrees and the system does not cycle ON very much.

Robert

[dngtig]

Most basic heat pumps defrost based on time and temperture.If the outdoor coil thermostat gets below 20-28 degrees depending on brand. The unit will allow a defrost cycle once the defrost timer as expired.The defrost timer can be adjusted for 30,60 or 90 minutes.Once defrost is initiated it will stay in defrost until either the outdoor coil reaches 75-80 degrees (again it depends on brand)or 10 minutes has expired.The other method of defrost which is more economical is demand defrost. Which will base its defrost schedule on oudoor temperture and coil temperture so it does not defrost unless really needed.Your heat pump can not be set for defrost 3 times an hour. In Ct we set the defrost for the max (90 minutes) due to lower humidity levels in winter but with global warming we haven't seen much winter yet.

[jackie stu]

YOUR PROBABLY LOW ON FREON

[rlj1117]

father in law in mt pleasant maybe take a trip and check it out, licensed in north and south carolina