ASHP on flat roof

[JamesPa]

Pretty much the only location for my ASHP is on the (easily accessible) flat roof of the garage.  The roof span is 2.7m and Im thinking about whether it would be sensible to support the ASHP on separate beams bearing on a part of the deck which is supported immediately underneath by the roof beams and is directly above the walls (so that effectively the support bears directly on the walls).  Thus there would be absolutely no chance that the roof deck becomes an amplifier for vibration and no doubt that the load can be supported.  The unit (Mitsubishi 11.2kW) weighs 120kg.  The load tables say that Unistruct P1001 will take the load easily, so that sitting on the usual type of feet for aircon is one option although that means it will be 175mm or so above the deck.

 

Am I over-thinking it, or is this a sensibly prudent approach?  Does anyone have any experience of a moderately heavy unit on a flat roof.  In a commercial environment aircon on a flat roof seems pretty much the norm, but for some reason domestic installers don't seem to like the idea.

 

All commentary/inspiration welcome.   

[HughF]

Paging @Marvin who has a cool energy 9kW unit on his flat roof.

[ReedRichards]

How will you get it up there?

[JamesPa]

3 minutes ago, ReedRichards said:

How will you get it up there?

Scissor lift most likely

 

I don't particularly like the solution, but literally the only viable alternatives are a long-run split, which I don't like either, or under a window at the front of the house, which i quite like (qith the right 'meaningful' design) but neither my wife nor the planning department do like.

[RichardL]

I've an idea you're outside permitted development if its on a roof and/or visible from the main road of the property.
Worth checking planning rules before committing.
 

[Marvin]

5 hours ago, HughF said:

Paging @Marvin who has a cool energy 9kW unit on his flat roof.

 

Only about 88kg though.

 

[Marvin]

https://www.planningportal.co.uk/permission/common-projects/heat-pumps/planning-permission-air-source-heat-pump#main-menu

[JamesPa]

13 minutes ago, Marvin said:

 

Only about 88kg though.

 

Thanks.  Any problems with vibration or noise transmission to the inside?  What's below?

[Marvin]

51 minutes ago, JamesPa said:

Thanks.  Any problems with vibration or noise transmission to the inside?  What's below?

Hi @JamesPa

 

Below is the utility room housing the buffer and hot water tank etc, and the end of the kitchen. Its been up there about 18 months. 

 

No vibration problems at all. Went for widest rubbery feet to absorb any vibration (but I must say even when running there seems to be none) and to distribute the load of a wide area.

 

Wife considers the noise level to be similar to the old gas boiler.

 

Marvin

 

 

 

[JamesPa]

10 hours ago, Marvin said:

Below is the utility room housing the buffer and hot water tank etc, and the end of the kitchen. Its been up there about 18 months. 

 

No vibration problems at all. Went for widest rubbery feet to absorb any vibration (but I must say even when running there seems to be none) and to distribute the load of a wide area.

That's really helpful thanks.  I plan to mount mine on beams bearing on the walls, not directly on the deck, which should reduce the noise transfer enen further.  Your post gives me the confidence to proceed.

 

Now I just need to find an installer who doesn't want to charge me an arm and a leg and put in loads of stuff I don't need!  I would DiY it, but my LPA is being stupid over noise levels so it needs to go in under PD, which means 'installed to MCS planning standards'.

[Conor]

Just a thought. If you have an ASHP on a flat roof, does that not mean that it is then classed as an area that has to be accessed regularly for maintenance and therefore edge protection / fall protection system is needed? E.g. ballustrading? Who's going to go up on to a wet, slippy rubber roof to check it? 

[JamesPa]

1 minute ago, Conor said:

Just a thought. If you have an ASHP on a flat roof, does that not mean that it is then classed as an area that has to be accessed regularly for maintenance and therefore edge protection / fall protection system is needed? E.g. ballustrading? Who's going to go up on to a wet, slippy rubber roof to check it? 

It needs access only occasionally so temporary balustrading will suffice.  I haven't yet worked this out in detail but my plan is to mount the unit on unistruct spanned so it bears directly above the walls, so the weight is supported directly on the walls.  The same unistruct base could support removable balustrading that can attach to the unistruct when in use, probably 'dropping in' and pinned.

[markc]

Mounting on long span unistrut or similar you could find the unit starts to oscillate and jump around like a bucking bronco, also any balustrade provided for maintenance will need to conform to load and deflection specs (you only need one savvy blame and claim merchant).

[JamesPa]

6 minutes ago, markc said:

Mounting on long span unistrut or similar you could find the unit starts to oscillate and jump around like a bucking bronco.

It might, but it's well within the maximum load spec if I use the back to back channel so unlikely.  If it does then an additional foot resting on the deck might be necessary, but it seems unlikely.

 

9 minutes ago, markc said:

any balustrade provided for maintenance will need to conform to load and deflection specs (you only need one savvy blame and claim merchant).

Indeed.  Ironically it might be safer _not_ to provide a balustrade and just ensure one of the many removable balustrade systems can be used.

 

PD specs require at least 1m between unit and edge of flat roof, presumably for this reason.

 

Heat pumps on flat roofs, or high up on walls, are pretty much the norm in the  commercial world (just wander down the back of your local high street/industrial estate.  The ones high up on walls in particular seem precarious, yet somehow they manage.

[JoeBano]

Hi, I’ve got a grant aerona3 10kw on my garage roof. It’s actually bolted to the house on an air conditioning bracket off eBay. I can hear it when’s it’s freezing cold outside and it’s doing hot water in my son’s room but I just leave it in quiet mode seems to do the trick. I have the older generation of aerona3 not the r32 which are supposed to be more quiet. 

[ReedRichards]

On 03/02/2023 at 09:55, JamesPa said:

Indeed.  Ironically it might be safer _not_ to provide a balustrade and just ensure one of the many removable balustrade systems can be used.

 

 

In my old house there was a flat roof above the living room extension which we made accessible by substituting a door for a long window.  We then sought permission to put a balustrade around it but this was refused, essentially on safety grounds.  The rationale was that with a balustrade in place we might then be tempted to throw a party (or some such) and fill the flat roof with a large quantity of people.  The extension had not been constructed to bear this amount of weight.  The absence of a balustrade would limit the numbers ever likely to be on the roof and therefore be, on balance, safer.  So we put plants in pots around most of the edges and just took care not to fall off.