Pipe size

[JackofAll]

Plumber has given me a list of items to get for second fixing house. Among them is 1"acorn piping and lagging for the flow and return to outside. According to heat pump installation guide it states 28mm copper or 35mm if using plastic. I've pointed this out and his reply was, usually use 1"acorn but your heat pump could be different. 

 

I know he's never fitted a monobloc HP before only split systems, but am concerned as he doesn't appear confident in comparison to other trades that I've dealt with. Should I be looking further afield?

[JohnMo]

How big is your heat pump?

 

Is the heat pump connected to a buffer, if so how far between the HP and buffer?

 

If no buffer how far to cylinder and heating system?

 

If UFH does include or not include a pump?

Edited November 21, 2024 by JohnMo

[JackofAll]

Thanks John.

 

9Kw.

 

There is a buffer that came with the kit, though not sure if he'll be using it. If he is, it will be 9/10 m from the HP.

 

Again 9/10m to cylinder from HP.

 

I believe there's a pump on the unit whether or not that would be fit to drive the water around a 1900 odd bungalow I've no clue, Imagine another would be required if not?

 

 

Edited November 21, 2024 by JackofAll

[JohnMo]

This is something heat geek put out there for pipe sizing, you will be looking at a dT of 5. So as you thought you need 28mm. The pipe your plumber is specifying is thick wall so closer to 22mm. I would have alarm bells ringing as he isn't doing the basics.

 

[JackofAll]

Just looking at the heat geek page as I needed to interpret that table. Am a little smarter now than when I woke up, thanks John. So there is no need for the buffer as per table. Re the plumber, it's what i thought, but God knows how long we'll have to wait to get a new guy this time of year.

[JamesPa]

1 hour ago, JackofAll said:

I know he's never fitted a monobloc HP before only split systems, but am concerned as he doesn't appear confident in comparison to other trades that I've dealt with. 

In a split its quite possible that the indoor unit is adjacent to (or integrated with) the DHW tank and point where the primaries to the heating system split off, and thus also possible that little or no 28mm is needed (the connections between the ODU and IDU in this case are refrigerant not water) and you would get away with a short length of 22mm at 9kW.  However he should know the difference!

[JackofAll]

Made a bubu when running ducts, not enough space to run the two pipes in one duct including insulation so now may have to run either the flow or return in a duct that has cables. Would this be OK considering it'll one length no joins? Alternatively we'd have to to go through the walls which I'd rather avoid unless necessary.

[ProDave]

34 minutes ago, JackofAll said:

so now may have to run either the flow or return in a duct that has cables. Would this be OK considering it'll one length no joins?

No, it would mean the cables being in a hot duct and probably insulated so they would have to be de rated.

[JackofAll]

47 minutes ago, ProDave said:

No, it would mean the cables being in a hot duct and probably insulated so they would have to be de rated.

Had to look up derating cables, actually the mains cable 25sq is running through and cables for the ASHP. Spark said not bout derating these, is this now an issue?

[JamesPa]

17 hours ago, JackofAll said:

Had to look up derating cables, actually the mains cable 25sq is running through and cables for the ASHP. Spark said not bout derating these, is this now an issue?

Depends on the rating (and derating characteristics) of the cable and the demand of the heat pump (or other load on the cable(s)).  Sparky should be able to advise the former and the spec of the heat pump (or other loads) the latter.  Don't forget to consider temp during legionella cycle if the heat pump does that natively (some do, some just switch on the immersion heater).  

 

I would definitely want to be certain its OK before going ahead, you really don't want smouldering cable on the coldest day of the year (which is when it will get hottest) causing a fire or taking your heating out!  If its not OK would it be more sensible to reroute the cable rather than the pipework  - cable routing is more flexible in all sorts of ways!

Edited December 27, 2024 by JamesPa

[JackofAll]

1 hour ago, JamesPa said:

Depends on the rating (and derating characteristics) of the cable and the demand of the heat pump (or other load on the cable(s)).  Sparky should be able to advise the former and the spec of the heat pump (or other loads) the latter.  Don't forget to consider temp during legionella cycle if the heat pump does that natively (some do, some just switch on the immersion heater).  

 

I would definitely want to be certain its OK before going ahead, you really don't want smouldering cable on the coldest day of the year (which is when it will get hottest) causing a fire or taking your heating out!  If its not OK would it be more sensible to reroute the cable rather than the pipework  - cable routing is more flexible in all sorts of ways!

Thanks James, will check with spark when he's back in January and plan to reroute the cables 

Edited December 27, 2024 by JackofAll