My heat pump is iced up.
Graham Hendra
Heat pump product development engineer. Author of heat pump text books. Heat pump builder.
Today was the first proper heat pump day, Cold and wet. see above
Contrary to popular belief heat pumps dont struggle in the cold, there is still loads of heat about when its -5C or even -10C in the garden. The thing that reduces output is cold and wet weather. In all heat pumps we run the coils 10 degrees below the air temperature, so if its around 0 degrees outside and humid the coil ices up really quickly. The water sticks to the coil like s**t to a blanket.
When I spec a heat pump I use the capacity output allowing for defrost see below. Notice how the capacity (in blue) dips between +5C and -5C, we call this defrost country. Below -5C the unit capacity rises because we dont need to defrost very much in really cold weather, there is less water in the air. If you went to the unit and measured the output at any given time it would be closer to the red line, this is the so called max (or idiots) output. But the unit can spend 6 minutes in every hour defrosting, so we de rate the output by 10% to be safe, hence the dip. Some people only publish the max output data for their units, I bet they are busy this morning.
Below is a photo of my street today, this is what we in the heat pump tech support service hate most. It means loads of calls from people saying my unit is a block of ice, (its not) and there is smoke coming out of my unit, (its steam) during defrost mode.
Its really normal to see a unit iced like the one in the title photo, this is how they look before a defrost. If there is something wrong with the unit the ice comes out past the tin work. if your unit looks like this, its frozen, you need an engineer.
Business Owner at Exi-tite Ltd, Exitech Digital and EXITITE Air filtration
4 年Jamie Herron
MD at Bruce Boucher Consulting & Design
4 年Refrigeration industry has been dealing with this for decades and decades nothing new. Trouble is home owners won't want to know, location of the unit can help. Also if you have a buffer, shouldn't really be a serious issue.
Managing Director and Climate Control Specialist at Logicool Air Conditioning & Heat Pumps Limited
4 年What about a hot gas bypass type defrost? Many of the systems out there seem to perform at constant heat outputs which is suspicious especially when you look at the spare parts list for each unit in the range. Losing some of that capacity to keep the coil from frosting gets that 10% loss back and would reduce defrost. It cannot be that difficult to have a solution such as a permanent brine circuit at the bottom of the coil either taking rejected heat from the compressor? Both of the above may be a little wide of the mark but I do wonder that with all the heat rejection technology and know-how we have that a simple idea may reduce the defrost cycle a little.
Green Chemical Engineer
4 年Sounds like we need a coating so the ice doesn't stick, it falls off, some have been looking, am not aware of any success. Designing for -3 deg C ambient as some heating engineers do will seem a bit odd in future as the planet warms. Low minimums are never coincident with when I'm awake and needing heat either.