How Does the Heat Pump Defrost Cycle Work?

[@raymondharrell2534]

Almost 3 years ago I replaced a 28 year old 12 SEER Rudd heat pump with a 20 SEER American Standard. It was the classical “rip and replace” with rule of thumb up-sizing. Your video has finally explained what multiple warranty call backs to the installer never seemed to be able to. Thank you for putting my mind at ease, somewhat. There are still many things that I am learning about my poorly informed decision regarding the heat pump. Your book and newsletters have put me on the right path. I will be in touch soon to obtain some of your company’s services to help me with the journey. I have researched the skill set and I can’t trust any of the local HVAC companies. Building science folks are few and far between here in northern ‘Bama. Thank you again.

[@TheEnergyVanguard]

I'm sorry to hear about your heat pump difficulties, Raymond. Unfortunately, it's all too common. When you're ready for HVAC design help, just reach out through our website at www.energyvanguard.com/hvac-design/. Thanks for the kind words and for buying the book! (For anyone wondering, here's the book he's talking about: energyvanguardstore.com/.)

[@ramsaymike]

The necessity of defrost is a bit of an 'Achilles heel' of heat pumps. In certain conditions the overall efficiency will be significantly reduced. It would be interesting to see heat pumps tested at highly frosting conditions. Also, to your point about the formation of frost at temperatures well above freezing, it would be interesting to see the data on the actual temperature of the outdoor coil (and compressor rate).

[@erikhansen4681]

this always amaze me, heat pump defrost, seen many installation direct to the ground or foundation without clearance from the units`bottom, are those places not experiencing outside temp freezing point and freezes the condense coming out from the defrost

[@GembG-tu4kb]

Hello. why does my new mitsubishi AY42 go to DF exactly every 30 minutes at a temperature of 4°C and lower even though there is no ice on the outdoor unit at all. Is it normal for DF to work exactly every time after 30 minutes without the conditions for it being met? Thank you

[@spazzman90]

While older and cheaper systems will activate defrost based on temp only (and subsequently have a 30,60,90 minute interval setting), newer systems should do better. My cheap Chinese units have no problems detecting when it is truly in need of a defrost. I suspect it's due to the fact that it monitors the intake and outgo air temp of the condenser and when they get too close, it figures out that it's blocked and needs a defrost. Of course its hard to find specifics online regarding that unit. Not sure which type yours would be, maybe there is a facebook or reddit group dedicated to that line of units.

[@DADoESofTX]

@@spazzman90 Did you mean to say that older/cheaper units activate defrost based on *time*?

[@spazzman90]

No. I said they activate defrost on temp. Specifically when the outdoor coil reaches 32f (ambient air could still be 37f or more). Once that threshold has been reached some units have a setting to run a defrost cycle every 30,60,90 mins. Your environment will dictate what you should have that set at. @@DADoESofTX

[@DADoESofTX]

@@spazzman90 Interesting. The circa 2004 lower-end Carrier unit that was originally at my house had the 30/60/90 jumper selection on the defrost control board. I always assumed that it triggered a defrost solely per the requisite minutes of accumulated run-time regardless of whether defrost was really needed. I sometimes noticed it running a defrost when there was no visible frost on the coils. The 2-stage Trane that replaced it a couple years ago functions much better in that respect.

[@orlonhall9856]

Not stand alone dehumidifier but it will remove a portion of humidity per hour.