Posted by: @heat-pump-newbie

Having just read on this forum about a cold well, I think my heat pump is in just that situation. I haven't found the details about taking temperature measurements though, suggested by @derek-m, just the blowing smoke comment. Please could you tell me more Derek ?

Our outdoor unit is in the 'back yard' which is a triangular space on the north side of our bungalow, with a 6 foot fence and tall hedge above one side, and the side of our garden room on the third side. The fan blows out towards the fence + hedge. There is a wide but solid gate on the inlet side of the pump, about 6 foot away from it, also a small shed away on the other side. The pump is the required distance from the house wall.

I'm thinking we should replace the solid gate with a slatted one as a start to get more airflow. Does this sound like a good idea ?

Hi,

Welcome to the forum.

Before making any alterations I would suggest that you carry out the simple temperature test. Using a thermometer, which doesn't have to be anything special or particularly accurate, since you are looking for a difference in temperature, measure the ambient air temperature well away from your ASHP, and obviously not in the backyard, then measure the temperature of the air around your ASHP. If you find quite a difference in temperature, then your ASHP may be pulling the exhausted cold air, back into the intake. This will of course reduce the efficiency of your system.

I would be interested to know what you find.

Thanks. I'll do that over the next few days. There's a breeze today, then it's going to get a bit calmer by Wednesday. I'll report back with full info to see of it changes with the wind.

@derek-m As it's so mild at the moment the HP isn't running much for me to take the temperature measurements, and then we're away at the weekend. I'll leave it till next week when no doubt it'll get cold again and I'll report my findings.

@derek-m I hope you can see from my pic here - the pump, shown as a thick red line, is located (at the correct distance) on the north east wall of the gable end of our bungalow. A 6 foot fence with our neighbour's tall thuja hedge runs at an angle away from our plot, with a wide but solid gate shown in turquoise to the east side of the yard. The garden room is about 10' high on the north side, and there's a small shed in the corner.

When the pump is running there's a cold blast bouncing off the fence and blowing back past the shed. As a first step I'm thinking I should dismantle that shed to give the cold air somewhere else to go. There is a second gate between the garden room and the corner of the house, but we always leave this open now for the cold air to escape. My second step could be to replace the solid gate with a slatted one to get new possibly warmer air in.

Initial temperature tests today gave about 2 degrees difference between the ambient air away from the yard and the air going into the back of the pump. Next week I'll have a proper go at the temperatures when the weather is colder.

I've been reading your suggestions about rigging up a cardboard shield to test the effect of 'new' air coming in from a higher level, I wonder if there's something permanent I could do like that? I can't really do much about the hedge, but possibly I could alter the fence to allow air through, though it does deflect off very well.

The installers chose this place because it was quite shielded and needed to be away from the boundary, which the south side is not. The indoor unit is above in the loft, but that's another story (no pun intended)!

Any advise would be gratefully received, thank you.

@heat-pump-newbie 

Before doing anything, I would suggest doing some more detailed testing when the weather is a little colder. The problem with ASHP's used for heating is that they expel cold air rather than the warm air coming out of an air conditioner used for indoor cooling. The cold air of course sinks rather than rising, and could collect in an enclosed area. The colder that the ambient air becomes, the harder the heat pump has to work, and the faster the fan will run, which in turn could produce even more, colder, air.

Whilst a 2C temperature difference may not seem of much importance in the great scheme of things, it can still equate to a 5% increase in energy consumption to operate your ASHP.

If time allows when you carry out your tests, try investigating the effect of having both gates closed, each gate open in turn and then both gates open. It may take some time for the 'well to fill' so to speak, so you may wish to get your wife or a suitable child to stand out in the cold measuring the temperature. 🙃 

@derek-m great idea - except I'm the wife ! Should I get my husband to lie down by the pump to block the cold air from going round the back !?

While he's getting used to the idea I think I'll get some smoke pellets to see if I can trace the flow of air, a joss stick wasn't smoky enough.

@heat-pump-newbie 

Having your husband try to block the cold air probably wouldn't work too well, unless he has a 'hot' body, since ASHP's crave heat. 😡

Sorry I'm not an expert on joss sticks. The smoke pellets are a good idea and may work quite well.

@derek-m Before I do this smoke test do you think the air pump itself would be ok if the smoke does get drawn back through ? I don't want to destroy anything. I've got 3g white smoke test cartridges: 45 seconds burn time, 5m3 volume.

@heat-pump-newbie That would be the only way to prove if the cold air is being recycled if it was drawn back into the HP. HPs are very robust and take environmental conditions with ease, so I would imagine inert smoke would do no harm.

Posted by: @heat-pump-newbie

@derek-m Before I do this smoke test do you think the air pump itself would be ok if the smoke does get drawn back through ? I don't want to destroy anything. I've got 3g white smoke test cartridges: 45 seconds burn time, 5m3 volume.

I'm afraid I'm not an expert on smoke either. What chemicals are involved in the production of the smoke. The air passing through the ASHP goes in at the rear and the side, past the finned heat exchanger, through the fan and out at the front, so as far as I am aware, they are the only parts that will be contacted by the smoke. I presume that you will be producing the smoke some distance from the heat pump, so by the time any reaches the internals it should be mixed fairly well. There will probably be something like 50m3 of air per minute going through the heat pump, so it probably will hardly notice any smoke.

Well that was very exciting ! I tried with the main gate shut and again with it open. The smoke blew right into the corner between the shed and the fence, then whirled around in a bit of a vortex, eventually clearing out into the back garden but not until it had filled the whole space, though not so much at the main gate end. It definitely circulated back into the pump whether the main gate was open or closed. I'll try again in colder weather but I think the shed's on a final warning, it's just too close to the pump.