So to today's questions on our ASHP install.

[MikeSharp01]

I am working on the tank end of the system now and that has thrown up some clarifications that I need to  be sure of:

 

1. Can I install the Thermostatic Mixing Valve (TMV) upside down as shown in the picture. (Cannot see what gravity has to do with the operation of such a valve)
2.  In connecting up the various overflows and the condensate drain from the Mechanical Heating and Ventilation Unit (MVHR) above the tank I need to get the final output into our main soil pipe.
   1. How far should I run it in copper? (As far as possible as you want it to cool down before it hits any plastic)
   2. How important are the details of the runs to the tundish(s) - seems like there is supposed to be 300mm of straight pipe into it etc... (I need to get the three pressure, one of which also has temperature, relief outflows into the pipe above the tundish.)
      1. Or would it be better / acceptable to go for three tundishes and join the flows below them?
   3. How do I connect copper to 32mm waste pipe? (Cannot seem to find a connector for this - do I make one from a blanking cap and tank fitting or some such? I did find this https://www.toolstation.com/tesla-tundish-universal-dry-trap/pAG239 but that goes directly from Tundish to 32mm so no room for cooling.)
   4. Can I get away with a waterless trap or do I need a full U bend in the plastic bit? (Waterless makes sense because it will get very little use so a U bend could / would dry out)
      1. Is there a waterless trap for 22mm Copper perhaps?
   5. As you can see from the image I have not yet connected the Heating loop from the ASHP to the expansion vessel. I assume it does not matter where in the heating circuit I make that connection as pressure difference arising from heating in the Domestic Hot Water (DHW) Loop and the UFH loop will manifest itself everywhere in the circuits. (I have no room for the expansion vessel elsewhere but I can run a long pipe to it from wherever in the circuit if needs be.)

 

 

[Marvin]

Easy one first:

 

3: https://www.bes.co.uk/push-fit-overflow-reducer-from-waste-32-x-215mm-11244/

[Marvin]

MVHR unit will trickle water when the outside temperature is lower than the inside temperature but doesn't need a tundish. It is meant to drip. Tundishes enable you to see that there is a fault because it is dripping.

 

My MVHR has a waterless trap which runs through 22mm plastic to a waste pipe connection.

 

The hot water to the tundish needs to be as the regulations show: max of two 15mm connected at the top. 22mm below copper all the way.

[Marvin]

One expansion vessel for the primary water circuit which connects the ASHP to the coil in tank and heating system.   

 

 

[SimonD]

Your D1 which is pipework up to the tundish must be in copper (metal to be more exact). This should be no more than 600mm in length. You can feed your prv/ t&p and condensate into 32/40/50mm waste no problem, even as a D2 after the tundish as long as the plastic is rated for the temperature.  But basically, if you have a waste serving several disharge pipes, this pipe must be at least one size larger that the D2 of the others. Probably better to copy and paste from G3:

 

Where a single common discharge pipe
serves more than one system, it should be
at least one pipe size larger than the largest
individual discharge pipe (D2) to be connected.
3.60 The discharge pipe should not be
connected to a soil discharge stack unless it can
be demonstrated that the soil discharge stack is
capable of safely withstanding temperatures of
the water discharged, in which case, it should:
a. contain a mechanical seal, not incorporating
a water trap, which allows water into the
branch pipe without allowing foul air from the
drain to be ventilated through the tundish;
b. be a separate branch pipe with no sanitary
appliances connected to it;
c. if plastic pipes are used as branch pipes
carrying discharge from a safety device, they
should be either polybutalene (PB) or cross-
linked polyethylene (PE-X) complying with
national standards such as Class S of BS
7291-2:2006 or Class S of BS 7291-3:2006
respectively; and
d. be continuously marked with a warning that
no sanitary appliances should be connected
to the pipe

 

So the question is whether your condensate pipe should even connect to this waste pipe serving the safety valves - probably not if there is risk that pressurised release can return back up into your MVHR. Personally I'd run them separately.

 

The discharge pipe should have a fall of 1:200.

 

If you're running the discharge pipes to the soil stacks it's frowned upon to use a strap boss - use a decent mechanical pipe boss like this: https://www.screwfix.com/p/mcalpine-mechanical-pipe-boss-connector-black-40mm/55722?gclsrc=3p.ds&gad_source=7&gad_campaignid=22478593832

 

Or this one:

https://www.toolstation.com/mcalpine-bossconn-22mm-soil-pipe-boss-connector/p57728  (this one though is a pain to cut the required shape in the soil pipe so I'd recommend the above instead).

 

For connecting 22mm to plastic waste pipes, this works well:

 

https://www.toolstation.com/mcalpine-overflow-universal-compression-plain-tail-reducer/p46778

 

Out of habit, I tend to put the expansion vessel on the return as I do the filling loop too. So don't forget the filling loop within this list of to-dos.

 

HTH as a start.

[JohnMo]

1 question if you are doing the UVC yourself, where are you getting the sign off certificate from? Assume you are not qualified, as you would ask the questions.

 

Hot water outlet pipe, I would drop pipe downwards at cylinder edge for about 150mm to stop thermosiphon.

 

Your grey and white expansion vessel is a maintained item, so you need access to the Schrader valves to pressurise - do you have access in that location?

 

1 hour ago, MikeSharp01 said:

Thermostatic Mixing Valve (TMV) upside down

Do you need one at all, certainly if you have secondary circulation loop you will have issues installing one with out carefully planning.

 

1 hour ago, MikeSharp01 said:

Can I get away with a waterless trap

Yes they are approved. You water less on MVHR also.

1 hour ago, MikeSharp01 said:

Heating loop from the ASHP to the expansion vesse

Ideally needs to be on the return line, but an isolating valve or similar device should NOT be installed between the boiler/heat pump and
expansion vessel which could isolate the expansion vessel from the system.

 

Edited yesterday at 12:32 by JohnMo

[SimonD]

13 minutes ago, JohnMo said:

but an isolating valve or similar device should NOT be installed between the boiler/heat pump and
expansion vessel which could isolate the expansion vessel from the system.

 

I always install these: https://www.unventedcomponentseurope.com/tesla-3-4-expansion-vessel-service-valve-2.html/

 

 

 

Oh, and @MikeSharp01, my usual practise is to have seperate tundish for heating and dhw cylinder as in future it makes life easy to diagnose a problem and where it's coming from.

[MikeSharp01]

2 hours ago, JohnMo said:

question if you are doing the UVC yourself, where are you getting the sign off certificate from? Assume you are not qualified, as you would ask the questions.

The Umbrella company are doing that alongside the MCS cert, hence me asking all the questions so I get it right and don't end up with problems. 

[MikeSharp01]

1 hour ago, SimonD said:

always install these: https://www.unventedcomponentseurope.com/tesla-3-4-expansion-vessel-service-valve-2.html/

 

That's already on the top of the small vessel should I also fit one to the big one?

[MikeSharp01]

2 hours ago, JohnMo said:

do you have access in that location?

Yes it's in a cupboard.

[MikeSharp01]

2 hours ago, JohnMo said:

if you have secondary circulation loop you will have issues installing one with out carefully planning.

No secondary circulation but need the TMV if I top up the UVC to 80+ with excess PV.

[MikeSharp01]

3 hours ago, SimonD said:

. be a separate branch pipe with no sanitary
appliances connected to it;

Oh - I was hoping to go into the main soil stack, center in image, in the corner of the room but if not I can round a bit and use the branch stack, right of center, which has nothing attached. 

[MikeSharp01]

4 hours ago, JohnMo said:

Ideally needs to be on the return line, but an isolating valve or similar device should NOT be installed between the boiler/heat pump and
expansion vessel which could isolate the expansion vessel from the system.

Does that not gain say what  @SimonD says he always fits by way of a service valve. 

[Nickfromwales]

4 hours ago, SimonD said:

 

I always install these: https://www.unventedcomponentseurope.com/tesla-3-4-expansion-vessel-service-valve-2.html/

 

 

 

Oh, and @MikeSharp01, my usual practise is to have seperate tundish for heating and dhw cylinder as in future it makes life easy to diagnose a problem and where it's coming from.

+1

 

Last one I installed has these. Much easier than a full drain down tbh.

 

 

These come with a wire that you push through for security, a bit like the DNO fits to the fuse and meter, to prevent misadventure.

[JohnMo]

It's a lockable valve. A normal service valve or a motorised valve isn't.

@Nickfromwales just beat me to it.

[Nickfromwales]

4 hours ago, JohnMo said:

 

Hot water outlet pipe, I would drop pipe downwards at cylinder edge for about 150mm to stop thermosiphon.

If there’s no hot return circuit & pump, I promote this heat creep (it’s not thermo syphon as it can’t loop back) to limit the amount of cold stagnant water that needs to be drawn off before getting premium hot water out of the taps. 
 

@MikeSharp01 you need a gap between the expansion vessel test valves. 

[JohnMo]

1 hour ago, Nickfromwales said:

not thermo syphon as it can’t loop back

Can't it - heat loss due to internal 'waterfalling' at pipe connections (tiny little thermal loops where warm water goes into pipe, cools and then falls back into tank, bringing more hot water into pipe). Sounds like a thermosyphon to me. Yes your pipe stays nice and warm at the expense of continuous heat loss, even with good insulation. How many if any seconds it saves you? Just had a shower secondary circulation off, cylinder 20m away from shower, in time it took to take clothes off, I walked straight into warm shower. I will keep the losses in check.

[MikeSharp01]

1 hour ago, Nickfromwales said:

If there’s no hot return circuit & pump, I promote this heat creep (it’s not thermo syphon as it can’t loop back) to limit the amount of cold stagnant water that needs to be drawn off before getting premium hot water out of the taps. 

I did think about installing the TMV directly above the tank outlet but decided it made everything more messy so its just at the edge of the tank.

 

20 minutes ago, JohnMo said:

How many if any seconds it saves you?

Not many but if it saves me having too much heat loss into the Utility room, where all this kit resides, I might just create a loop as you suggest.

 

1 hour ago, Nickfromwales said:

you need a gap between the expansion vessel test valves. 

Sorry not clear what you mean, you can get my pump onto the Schrader valves of both vessels as they are placed in the picture, the view angle makes it look like they are very close together or are you referring to something else?

 

There is no room below the large vessel for one of those service valves but I could put the valve to one side or possibly lift both vessels up but the upper one will start to interfere with the hot and cold water manifolds which will be above it. Alternatively I could mount the large vessel horizontally if that is allowed?

Edited 19 hours ago by MikeSharp01
Added last sentence.

[SimonD]

6 hours ago, MikeSharp01 said:

Oh - I was hoping to go into the main soil stack, center in image, in the corner of the room but if not I can round a bit and use the branch stack, right of center, which has nothing attached. 

 

The waste serving as your D2 can go into the soil stack even if that soil stack has other sanitary appliances attached. You just can't have other sanitary appliances attached to the D2 pipe to the soil stack. Hope that makes sense?

[Nickfromwales]

6 hours ago, JohnMo said:

It's a lockable valve. A normal service valve or a motorised valve isn't.

@Nickfromwales just beat me to it.

You snooze, you lose fella.   

[Nickfromwales]

1 hour ago, SimonD said:

 

The waste serving as your D2 can go into the soil stack even if that soil stack has other sanitary appliances attached. You just can't have other sanitary appliances attached to the D2 pipe to the soil stack. Hope that makes sense?

Nope. That's as clear as mud lol.

 

Try again please, as even I am confused by that one!  

[Nickfromwales]

5 hours ago, JohnMo said:

Can't it - heat loss due to internal 'waterfalling' at pipe connections (tiny little thermal loops where warm water goes into pipe, cools and then falls back into tank, bringing more hot water into pipe). Sounds like a thermosyphon to me. Yes your pipe stays nice and warm at the expense of continuous heat loss, even with good insulation. How many if any seconds it saves you? Just had a shower secondary circulation off, cylinder 20m away from shower, in time it took to take clothes off, I walked straight into warm shower. I will keep the losses in check.

Do the same with the basin hot tap and report back please. You can keep your clothes on for that one  

 

The expense of continuous heat loss? C'mon..... we're talking pennies and the benefit outweighs the long term losses of the discharged cold water through the meter.

 

Happy to stay up and fight for this one, as I'll win.

[Nickfromwales]

4 hours ago, MikeSharp01 said:

Not many but if it saves me having too much heat loss into the Utility room, where all this kit resides, I might just create a loop as you suggest.

You just insulate the pipe, then the heat (loss) is contained  but the slug of cold water is deleted.

 

Straight off the cylinder is the larger bore, 22mm or 28mm sometimes, hot water pipework, so when running a basin hot tapo this becomes way more of an issue; dumping out the cold water before getting hot out of the tap to wash hands after using the loo.

 

For the shower, or a bath, or filling the kitchen sink, utterly irrelevant, just way more of an issue with frequent use, low flow outlets such as basins. If you're happy to stay fully clothed and wash your hands in tepid water, please ignore me and loop away. FYI, I've never done that loop on a pressurised unvented cylinder setup, and never will. I only do a more significant anti-gravity loop if it's a vented cylinder and the CWS is constantly heated / 'hot'.

[MikeSharp01]

8 hours ago, SimonD said:

The waste serving as your D2 can go into the soil stack even if that soil stack has other sanitary appliances attached. You just can't have other sanitary appliances attached to the D2 pipe to the soil stack. Hope that makes sense?

Yes that makes sense. So "b. be a separate branch pipe with no sanitary appliances connected to it;" means (not implies) the D2 pipe is a branch pipe itself? Hope that helps @Nickfromwales  

[SimonD]

10 hours ago, Nickfromwales said:

Nope. That's as clear as mud lol.

 

Try again please, as even I am confused by that one!  

 

Pls see @MikeSharp01 comment below which clearly says it better than I ever could. Thankfully he woke up this morning with a clear head, unlike you and me that get into discussions late at night when we should probably be getting some sleep, or at least I know I should've been! 😁

 

4 hours ago, MikeSharp01 said:

Yes that makes sense. So "b. be a separate branch pipe with no sanitary appliances connected to it;" means (not implies) the D2 pipe is a branch pipe itself? Hope that helps @Nickfromwales