Ground source heat pump cooling

[Sunrisemike]

My son is considering installing a heat pump. He has a stream running past his garden about 15 meters away. He has been advised that he could circulate the water from the stream through the unit, providing the means of heating or cooling the house. This sounds fine, but cooling through existing radiators presumably is problematic. Would this cause considerable condensation on the radiators? I can only think that it would mean using a fan to circulate the cool air and a dip tray to catch the condensate would be the answer. It's not many days in the summer that you need it. Any thoughts?

Mike

[Stinsy]

Cooling via rads will cause them to stream condensation. Underfloor works though.

Extracting heat from a stream 15m away seems like a complex and expensive endeavour. Are the benefits worth it vs air-source?

[ALAN/ALAN D]

As you say. Not many days in summer required for cooling. Plastic pot to catch drips. On mine the drips always drop in the same place. Has he got room thermostats / thermostatic valves on each radiator or underfloor system loop. If so you will need a switch / relay system to over ride the thermostatic valves for cooling. Or just remove the valve tops for cooling days. Mine has a thermostat / valve for each room.
Are the existing radiators big enough to run at a lower heating temperature that you will get from the heat pump. What is the heat pump temperature that’s specified. My system uses under floor pipe work. Only got two wall mounted radiators.

What filters will be used to stop muck from water stream being sucked in. ?

[Stinsy]

What filters will be used to stop muck from water stream being sucked in. ?

It'll be "closed loop" for several reasons, with "open loop": you risk freezing the HP, you massively increase energy consumed pumping the water, and you increase problems with silt/etc.

[Oldgreybeard]

I have been looking into this, but with an ASHP. They will run in cooling mode so can be used to cool the house but there are issues with using radiators, as mentioned above. I heard of two people that had been using their ASHP to cool their UFH and they both reported that it works well, so this what I'm now doing. AS long as the floor surface temperature remains above the local dew point then there are no problems with doing this. In reality this means you can cool the floor down to at least 18 deg C without causing any risk, but you need to know the indoor air temperature and relative humidity so you can check the dewpoint. For example, right now the indoor RH is 45% and the temperature is 20.8 deg C, so the dewpoint is 8.4 deg C. As long as the floor stays well above that then it will remain dry.

The same goes for radiators, keep them above the local dewpoint and they won't get damp. The snag with radiators is that unless they are top fed they won't work for cooling. The Heat Geek on YouTube tried this recently, and although it sort of worked a bit he needed to fit fans to the radiators and he did find they condensed water along the lower edge. He also found that only the bottom of the radiators was getting cooled, because the radiators were standard bottom fed ones. I think he did set the flow temperature to too low a temperature as well.

From what I've read, as long as the heat pump flow temperature is such that no exposed surface (including any pipes) can get below the local dewpoint then you are OK. My experience is a bit limited but I did try this in the heat wave recently and it did work pretty well. Main downsides are that it is very slow to cool the house down, it takes about a day of it being on for the effect to get noticeable. Also, it does make your feet cold if you have a solid floor where you sit (my office has a tiled floor - I need to keep my feet on an offcut of insulation to stop them getting cold).

Overall the effect of floor cooling is useful in the sense that it tends to stabilise the house temperature and stop the big swings, but it is nowhere near as effective as fitting window awnings to keep the sun out, nor is it as effective as fitting an A2A unit in our bedroom. The big benefit of the A2A unit is that it cools very quickly, so if you do let the house get too hot it brings the temperature down in half an hour or so. Better still is to stop the heat getting in in the first place, and the fairly cheap (around £70 to £120 depending on size) drop-arm awnings I fitted a few weeks ago do a very good job of that.

One thing I have been thinking about is making up a water to air heat exchanger to plumb into the heat pump. I think that could work as well as the air con unit and the condensation problem could be addressed the same way, by collecting the drips and sending them out of a drain pipe.

[Sunrisemike]

Thanks all for your replies.

His present system is pretty naff. They are mostly very long shallow rads with ventilation covers to hide them. Being close to the stream and with trees to the east, it seldom gets that hot inside, it's mostly planning for more of these "rare" heat events. He could just buy a coupe of coolers for the bedroom and sitting room.

The stream has no sediment and is clear water. Obviously it needs a filter at the stream end, but fine particles shouldn't be a problem as the water is simply being pumped round through the heat exchanger. I would have thought a circulating pump would draw less power than the massive fans needed for ASHP. As far as I can see, the benefits of GSHP is that it is a lot quieter, smaller and more efficient than ASHP. Laying a suction and return pipe should be far cheaper than digging in pipe work to extract heat from the garden.

Catching a few drips from a radiator doesn't sound too in intimidating to me.

Mike.

cooled by the sea-breeze.

[Stinsy]

I have been looking into this, but with an ASHP. They will run in cooling mode so can be used to cool the house but there are issues with using radiators, as mentioned above. I heard of two people that had been using their ASHP to cool their UFH and they both reported that it works well, so this what I'm now doing. AS long as the floor surface temperature remains above the local dew point then there are no problems with doing this. In reality this means you can cool the floor down to at least 18 deg C without causing any risk, but you need to know the indoor air temperature and relative humidity so you can check the dewpoint. For example, right now the indoor RH is 45% and the temperature is 20.8 deg C, so the dewpoint is 8.4 deg C. As long as the floor stays well above that then it will remain dry.

The same goes for radiators, keep them above the local dewpoint and they won't get damp. The snag with radiators is that unless they are top fed they won't work for cooling. The Heat Geek on YouTube tried this recently, and although it sort of worked a bit he needed to fit fans to the radiators and he did find they condensed water along the lower edge. He also found that only the bottom of the radiators was getting cooled, because the radiators were standard bottom fed ones. I think he did set the flow temperature to too low a temperature as well.

From what I've read, as long as the heat pump flow temperature is such that no exposed surface (including any pipes) can get below the local dewpoint then you are OK. My experience is a bit limited but I did try this in the heat wave recently and it did work pretty well. Main downsides are that it is very slow to cool the house down, it takes about a day of it being on for the effect to get noticeable. Also, it does make your feet cold if you have a solid floor where you sit (my office has a tiled floor - I need to keep my feet on an offcut of insulation to stop them getting cold).

Overall the effect of floor cooling is useful in the sense that it tends to stabilise the house temperature and stop the big swings, but it is nowhere near as effective as fitting window awnings to keep the sun out, nor is it as effective as fitting an A2A unit in our bedroom. The big benefit of the A2A unit is that it cools very quickly, so if you do let the house get too hot it brings the temperature down in half an hour or so. Better still is to stop the heat getting in in the first place, and the fairly cheap (around £70 to £120 depending on size) drop-arm awnings I fitted a few weeks ago do a very good job of that.

One thing I have been thinking about is making up a water to air heat exchanger to plumb into the heat pump. I think that could work as well as the air con unit and the condensation problem could be addressed the same way, by collecting the drips and sending them out of a drain pipe.

Good post!

Are you measuring RH inside your house or getting it from the weather forecast? I guess RH inside your home would be much higher than outside unless very well ventilated. On the other hand a probable dehumidifier could significantly increase the amount of “dew free” cooling you’re able to undertake.

In my 1-week experience using a single A2A to cool my entire 5-bed house: I’ve noticed it produces a huge amount of condensate. I’ve been monitoring it closely because the A2A is on an internal wall and a condensate pump was therefore required.

[Oldgreybeard]

Good post!

Are you measuring RH inside your house or getting it from the weather forecast? I guess RH inside your home would be much higher than outside unless very well ventilated. On the other hand a probable dehumidifier could significantly increase the amount of “dew free” cooling you’re able to undertake.

In my 1-week experience using a single A2A to cool my entire 5-bed house: I’ve noticed it produces a huge amount of condensate. I’ve been monitoring it closely because the A2A is on an internal wall and a condensate pump was therefore required.

Thanks, over the past few days I'm coming around to the view that it works better than I first thought. It takes a long time of the heat pump running in cooling mode for it to give its best, no idea why, but it is cycling a lot, as the cooling load isn't very high (not that big a temperature differential between flow and return).

I can measure RH inside and out, but there isn't usually a big difference, as any difference is pretty much wholly down to the air temperature difference. Right now the heat pump (which has a humidity sensor at the rear) is showing 49% at 17.2°C, the indoor sensor in the hall is showing 43% at 20.4°C. This gives an indoor dew point of 7.4°C and an outdoor dew point of 6.4° C, so not a massive difference in absolute humidity, 0.008kg/m³ indoors, 0.007kg/m³ outdoors.

The air con in the bedroom has been on 24/7 for days, and like you've seen, the condensate pipe is constantly dripping (I have it feeding our water butt - every little helps) so that is probably drying the indoor air a fair bit.