Air source heat pumps (ASHP) and drainage - Why do heat pumps emit so much water?

They do, from the humidity of the outside air. It condenses on the grille and drips off onto the ground or into a drip tray. That water has to be directed away to a drain. On a humid day it’s surprising just how much water runs off.

That’s what can freeze on the grille, which needs the defrost cycle to melt it off. 

Depends on the size of unit and weather conditions. I've seen values of up to 10 litres per hour quoted. Potentially a problem if it just leaks across a path and starts to freeze as the condensate will keep building up in cold weather.

Or as of 3 days ago drips out the front left base of the heat pump as well ! Zero rainfall.

Thanks for your comments on this question. I’ve separated this out into it’s own topic and put it in the public forum so that it can help others searching for this advice. 

So @juliamc @nealmurphy @hambrook does that means every heat pump needs to have some form of deliberate drainage below it? The most common I’ve seen from the trials we’re running is the pump raised off the ground, above loose gravel. But @hambrook doesn’t have this. Will that water be directed below or to the side of that decking? 

What happens if someone's heat pump is going to be placed above tarmac or concrete? 

There should be some drainage (in the same way that a condensing boiler needs a drain). Ours is piped to a nearby drain, although there was a puddle under it this morning so I wonder if the pipe isn't connected properly.

Ours had this drip tray to collect the water which then flows away into nearby drain:

Ours had this drip tray to collect the water which then flows away into nearby drain:

 

Hi Julia

Hi Julia, Re your ASHP drip tray. I’ve just had a Daikin split ASHP installed with a R32 inverter. All working well except for the drips as no tray was installed. My installer doesn’t seem to have a good solution. Are you able to tell me the make of the drip tray or the name of the company who installed yours so that I can hunt down a solution. I would be extremely greatfull. Many thanks Martin 

Hi ​@Martinrthomas Ah ! So that’s where you saw the drip tray. When it was newly installed I thought it was a good idea, now I’ve seen it over a few winters I realise it was completely the wrong thing. It gets filled up with leaves and as the hp is on a slight slope the ice forms in the tray. Also the drainage pipe fro it is ridiculously thin and ices up itself. The correct way to manage the water/ice forming on the unit is to have a proper drain or soakaway and sit the unit on that, no drip tray involved. Should be done before the unit is installed.

​@Martinrthomas 

Further to the above, retrofitting a drip tray on this split system should have been done with the refrigerant removed prior to moving the unit. This wasn’t done in my case, resulting in a significant leak of R32. Long story. 
What surface does your unit sit on ? Can you post a photo of it ?

Thanks for your reply. I would still like to know where the tray came from or who provided it please as I would like one. My installer used a core drill to make. 30cm drain under the pump. The difficulty is without a drip tray the water spills everywhere as there is nothing to collect it to run into the drain under the unit. Your drain tray looks like a genuine Daikin one but we are struggling to track it down so help in finding one for me would be very much appreciated. Thanks 

PS Heating otherwise great

I’m sure the part I have on mine is this or very close to it:

https://phc.parts/product/oem-spare-parts-348634/DrainPanforDaiki-DA8280/DA8280?srsltid=AfmBOorPM7RQfz0BpWb2g9qKfuicG7UsTEUslYrNQ_dlotKvRdellhj_3y8

However, it really needs to be fitted while there is no refrigerant in the unit, and before the pipework is connected. You have a very neatly installed HP there, I would be very happy if mine looked as tidy. I’ve seen other units with paving underneath where the installer has left slightly wider gaps between the slabs and not pointed (grouted?) them so the condensation drains away between the slabs. Of course that would also have been done before the unit was put in place.

Great and many thanks 

This looks like the one, I’ve passed the info to my installer 

I am hoping to get a different installer to alter mine as it’s a real mess now. I hope I can get a proper drainage soak away or something similar and a bed of gravel for the whole thing to sit on. And in my case also to lift it up onto a stand to help the airflow and leaf problem. 

​@Martinrthomas maybe think outside the box a bit.

Loooking at that it is already pretty neat and personally I would just make a ‘L’ frame with say 12mm x 12mm timber battens to sit on the flags, round the unit to the walls, and fill it with a shallow layer of pea gravel or similar. (making sure not to cover that 30mm drain).
It should cost less than £20 to do that. (Depending mainly on your chosen gravel).

That should hide the dripped condensate, it would be under the gravel, while not looking out of place there.
In fact it would probably look much better than a metal/plastic drip tray.

Just to show how totally useless my drip tray is !!

And after we’d swept every leaf away from our garden and went away for a weekend this lot blew in under our fence:

This is what I would like...

And this is a snapshot from a YouTube video of a Daikin owner’s installation. 

Thanks for the pics. Fortunately I wouldn’t have that leaf problem and have a drain under the unit but both to collect and direct the run off. I can see the outlet pipe is a problem far too small and has no drop so will freeze giving the condense no where to go  There should be a small length of  flexible hose about 3-4cm in diameter from the tray discharging straight into a drain under the unit. Perhaps some mesh or netting wrapped around the base could fend of the leafs. All the best with yours