Hot/Cold water buffers - benefits?

[puntloos]

Recently saw a design of a house that had:

- ASHP

- Hot water main cylinder

- Hot water buffer

- Cold water buffer

 

Can anyone tell me what the 'point' of these buffers is? Obviously they can somewhat act as 'heat/cold batteries' but no idea if that's a big deal or if it's only going to help something in the most extreme circumstances (such as hosting 5 extra guests, or the hottest/coldest days of the year?

[Temp]

The Hot water cylinder is for DHW. ASHP are generally sized too small to provide instant hot water.

 

The hot buffer is to reduce short cycling of the ASHP when driving UFH or rads with lots of zones.  Eg when only one calls for heat it can draw it from the buffer and not have to turn on the ASHP. Being seperate to the DHW tank allows it to run at say 40C instead of 60C which improves the COP of the ASHP.

 

What sort of cold buffer? Cold water accumulators are sometimes used to boost flow rates if the house is a long way from the main and the pipe is small/scaled up. They fill up with mains pressure water slowly then release it quickly when a tap or shower is opened.

Edited July 26, 2021 by Temp

[puntloos]

52 minutes ago, Temp said:

The Hot water cylinder is for DHW. ASHP are generally sized too small to provide instant hot water.

Interesting, sounds like a good idea if you have a little space to store it.

 

48 minutes ago, Temp said:

What sort of cold buffer? Cold water accumulators are sometimes used to boost flow rates if the house is a long way from the main and the pipe is small/scaled up. They fill up with mains pressure water slowly then release it quickly when a tap or shower is opened.

 

Honestly I don't know, I went to a M&E team's site and they showed me a hot and cold buffer. (not a newbuild, and a fairly large house).

Presumably though your heating rationale would apply to cooling too? If the house wants to be cooled you can draw on it without instantly engaging the thing? 

 

 

[Temp]

Sorry if you already know this but the red thing is most likely an expansion vessel. Stops pipes bursting when the water in the heating system expands as it gets hot.

[puntloos]

7 minutes ago, Temp said:

Sorry if you already know this but the red thing is most likely an expansion vessel. Stops pipes bursting when the water in the heating system expands as it gets hot.

 

Embarassingly(?) recently I wouldn't have known for sure. But no I am 98% certain that the actual DHW cylinder is not in the picture. 

[joth]

Simultaneous heating and cooling is very common in commercial buildings. My office is only a couple years old and has no ceiling tiles so very easy to see the M&E and get an idea how it all works. 4 pipe system circulates hot and cold to all rooms simultaneously and each fancoil can choice which to use. A central heat pump can move energy between the loops so literally pumping heat from the overheating areas  to the places that need it more. Topping up from district heating in winter, or dumping excess to the roof air exchangers in summer.

 

4 pipe systems generally circulate refrigerant rather than water, I have no idea how the buffering works.

 

In a domestic home I can see it being useful in a tall house with numerous floors, to pump excess heat accumulating in the roof back down into the UFH. More of an issue the more you keep internal doors closed. Getting cats has greatly changed our own patterns of use and impacts the idea M&E system design more than I imagined!

 

 

[SteamyTea]

5 hours ago, joth said:

 

In a domestic home I can see it being useful in a tall house with numerous floors, to pump excess heat accumulating in the roof back down into the UFH

Mate of mines company tried that, got close to freezing as there was not enough airflow. MVHR is better, and cheaper.

Or an exhaust ASHP.

[joth]

2 minutes ago, SteamyTea said:

Mate of mines company tried that, got close to freezing as there was not enough airflow. MVHR is better, and cheaper.

Or an exhaust ASHP.

OK so it doesn't work for N=1 sample size, but that could just as easily be they didn't design it to have sufficient airflow.

I would not use this as a replacement for MVHR, providing heating / cooling vs providing fresh air, seem to me best done by two different systems.  MVHR is not a solution for overheating. ASHP+Fancoil is not a solution for supplying fresh air.

 

 

 

[SteamyTea]

1 hour ago, joth said:

OK so it doesn't work for N=1 sample size, but that could just as easily be they didn't design it to have sufficient airflow.

Yes, not conclusive, but it is a hard sell to customers when you turn up with a drill and a foot diameter hole cutter.

1 hour ago, joth said:

MVHR is not a solution for overheating

No it isn't.

A silver roof is, or failing that, there are now some paints that are dark but still reflect a significant amount.

PV on the roof is the obvious solution.  That will suck out 20% of the energy on a good day, just in electricity, and a fair amount by reflection, depending on the angle of incident.

 

Edited July 26, 2021 by SteamyTea

[puntloos]

20 minutes ago, SteamyTea said:

Yes, not conclusive, but it is a hard sell to customers when you turn up with a drill and a foot diameter hole cutter.

But in my particular situation I actually am designing a 600x600 whole house (vertical) service shaft anyway so by itself it's not a problem to accommodate.

 

20 minutes ago, SteamyTea said:

No it isn't.

A silver roof is, or failing that, there are now some paints that are dark but still reflect a significant amount.

PV on the roof is the obvious solution.  That will suck out 20% of the energy on a good day, just in electricity, and a fair amount by reflection, depending on the angle of incident.

 

Not sure I'm wrapping my head around this yet. Of course(?) MVHR can .. HR - so indeed pulling hot air from the loft doesn't seem too crazy if it's available (I do have a central hall with skylights all the way up, could even consider trying to pull away heat there. 

 

But for "harvesting cold" into a cold buffer I think we can certainly see the same principles apply, when immediate cooling is needed, have a bucket of cold water at the ready - possibly collected at night - rather than doing this when the heat is greatest not to mention elec. prices are highest (but I guess also solar is highest)

 

But when it comes to cold buffer, I am certainly planning either a central coil beast

 

 

Perhaps AND / OR - augmented with per-room fancoils

 

and possibly cold water UFH (not a fan, condensation.. but might be controllable)

 

[SteamyTea]

21 minutes ago, puntloos said:

But in my particular situation I actually am designing a 600x600 whole house (vertical) service shaft anyway so by itself it's not a problem to accommodate

I think that is a great idea. Nothing to stop you moving a lot of air through it as well. Just need some filters to catch the bits. A couple of fans, set at an angle to each other, could move tonnes of air almost silently. I think this idea needs exploring more.

 

Where in Herts are you?

Edited July 26, 2021 by SteamyTea

[puntloos]

4 minutes ago, SteamyTea said:

I think that is a great idea. Nothing to stop you moving a lot of air through it as well. Just need some filters to catch the bits. A couple of fans, set at an angle to each other, could move tonnes of air almost silently. I think this idea needs exploring more.

 

Yes the 600x600 was intended for those huge insulated air pipes. Was somewhat (re)debating a dumbwaiter as well (for the laundry) but I'm not sure where I can fit it.

 

Current (v. provisional) basement design: (with the yellow thing being the 600x600 shaft. (dodgily drawn but you get the idea)

4 minutes ago, SteamyTea said:

Where in Herts are you?

St Albans area

[SteamyTea]

1 minute ago, puntloos said:

St Albans area

Used to live just up the road in Abbot's Langley.

Had some nice times in the grounds if the Abbey, especially when they had no traffic wardens in the area.

[TonyT]

Make sure the shaft is fire stopped once services are complete, risers make lovely chimneys!

[puntloos]

3 hours ago, TonyT said:

Make sure the shaft is fire stopped once services are complete, risers make lovely chimneys!

 

Good shout. I hope/assume my SE/Arch will handle it properly but never hurts to doublecheck

[TonyT]

If it’s not detailed who will be looking at the riser, no one will be taking responsibility.

 

so best to ask the question now