ASHP installation / mount point and draingage

[Jeremy]

I'm installing a 16kw air source heat pump next week, and need to put in a spot to anchor it. I'm wondering if people can comment on how they've installed them and what has worked? I'm aware this ASHP will put off a lot of water (60-100l a day) and there's an inlet for sewer/waste water (it's a combined one system) about 4ft away from the installation point I've chosen. Should I put down some combination of sand, gravel and top off with cement? Or just small cement bits for the footings for the ASHP mount points? And what about water drainage? I can run some 40mm pipe from top of the pad, or a kind of soakaway. I'm just not quite sure whether 100l is too much to just drain in place. The ASHP is downslope slightly from the sewer inlet which is only about 2" below ground, so it's likely I'd need to run pipes above ground from ASHP. Would love to hear what you've done, and what has worked - and photos if you have 'em!

[Jeremy]

Here's a photo of the site:

 

[ProDave]

Those air bricks worry me.  You want your pad lower than the air bricks, that is the last place you want any condensate going.

 

Mine (only 5kW) just sits on 2 paving slabs bedded on sand on compacted hardcore, and any condensate just runs into the surrounding ground.

 

[joe90]

I concur with @ProDave you don’t want water/condensation entering those air bricks. I built a concrete pad for mine with gravel down the back fir drainage.

 

Edited June 18, 2021 by joe90

[Jeremy]

Good point - it's funny what you don't think about even when you're staring straight at it! So I'll excavate down a bit (maybe 6"?) put down hardcore (how much? maybe 3"?), compact it, and then put down sand (1" maybe?). Manufacturer requirement is 150mm (6") away from the wall, so maybe I will also move the site further forward from the wall than that (maybe 12"?).

 

General consensus that it's not worth trying to run a pipe for drainage?

[joe90]

29 minutes ago, Jeremy said:

General consensus that it's not worth trying to run a pipe for drainage?

Mine is above a French drain, depends on your soil type, mine does not produce much at all.

[TonyT]

Put a floor drain into a concrete slab and tie it into the rainwater pipe work that’s close by.

larger units generate more condensate

I have a 70kW ASHP at work done in this manner worked perfectly since installed in 2013.

[Jeremy]

23 minutes ago, TonyT said:

Put a floor drain into a concrete slab and tie it into the rainwater pipe work that’s close by.

larger units generate more condensate

I have a 70kW ASHP at work done in this manner worked perfectly since installed in 2013.

 

That's what I was considering (something a bit like this: http://www.primagem.org/how-to-install-a-floor-drain-in-concrete-slab/) - can you detail how you tied into the rainwater pipes?

My slight concern here is how to get gravity working for me on the drain if it goes below the slab. Does yours sit above ground level like @joe90 ?

[Jeremy]

1 hour ago, ProDave said:

Those air bricks worry me.  You want your pad lower than the air bricks, that is the last place you want any condensate going.

 

Mine (only 5kW) just sits on 2 paving slabs bedded on sand on compacted hardcore, and any condensate just runs into the surrounding ground.

 

 

 

@ProDave Did you mortar in the slabs when you installed that?

[TonyT]

54 minutes ago, Jeremy said:

 

That's what I was considering (something a bit like this: http://www.primagem.org/how-to-install-a-floor-drain-in-concrete-slab/) - can you detail how you tied into the rainwater pipes?

My slight concern here is how to get gravity working for me on the drain if it goes below the slab. Does yours sit above ground level like @joe90 ?

Ours sits in a 6” thick concrete slab above ground level

[ProDave]

3 hours ago, Jeremy said:

 

@ProDave Did you mortar in the slabs when you installed that?

No. And they have not moved.

 

The area behind and to the left hand side is just filled in with stones so acts as a French Drain for condensate.

[dpmiller]

Mine sits on flexifeet, on an extended step at the back door. There's a rear-entry gully there which gets some of the condensate. I also isolated the step from the wall of the house with a sheet of polystyrene before the pour to be doubly-sure of no vibration transfer...