Class A, B, C Hot water cylinder in Passivhaus

[puntloos]

So I've designed my under-stair cupboard to accomodate a hot water cylinder in the center of the picture below. A 400L class-C cylinder, the one I designed in is a https://www.gledhill.net/products/alternative-energy/stainlesslite-heat-pump/ 

 

My contractor points out that "class C" will heat up the place, shedding heat into the under-stair, as well as rest of the house which is Passivhaus spec!. Class A is nice of course, but I could only fit, maybe, a https://www.osohotwater.com/product/indirect-hot-water-cylinder-dgc/ which goes up to 300L "only". 

 

Should I really try to spend and fit the fancy one? Or is class C fine, even for passivhaus

 

 

[AliG]

The first cylinder lists the heat loss as 87W for 400l.

 

The second one lists 70W for 300l.

 

I doubt 17W will make much of a difference (presumably that is 0.4kWh a day)

 

The standing losses for a tank are calculated at 65C, so would be reduced by 20-25% if you keep the water at 55C.

 

A lo of the losses come from pipework etc as much as the tank, so it is important that they are all insulated.

 

There may be other things to consider such as was one designed for an ASHP vs a boiler.

[Nickfromwales]

A bog standard Telford stainless ( lifetime warranty ) will lose at or below 1^oC per hour at these temps.

Even at 70^oC these are cold to the touch.

The thing that is out of touch, is your contractor...... With proper pipe insulation local to this cylinder, you absolutely will not have an auxiliary heating system from DHW.

If this gets routinely heated by excess PV during the summer months then the numbers warp a little, but you could still simply turn the immersion set-point a bit lower, to say 65^oC, to mitigate.

Edited November 11, 2022 by Nickfromwales

[ProDave]

What do the heat loss calculations actually say your heat input requirement is?

 

If the (much less than) 70W heat loss from the cylinder is going to overheat your house, then you better not let any people into the house (300W per person) and most certainly don't let them do any cooking.

[AliG]

Yes, heat loss from the cylinder over 24h would be roughly the same as having the oven on for an hour.

[Nickfromwales]

44 minutes ago, AliG said:

Yes, heat loss from the cylinder over 24h would be roughly the same as having the oven on for an hour.

Except the oven would be in an open room, and the OP's cylinder is locked in a cupboard, eg significantly less convection / direct conveyance of the latent heat to room / whole-of-house.

[Nickfromwales]

53 minutes ago, ProDave said:

you better not let any people into the house (300W per person)

...and shoot the dog!  

[billt]

1 hour ago, ProDave said:

 then you better not let any people into the house (300W per person)

 

I think not, more like 100W average.

[Nickfromwales]

5 minutes ago, billt said:

 

I think not, more like 100W average.

Depends whether or not they brought their Peleton bikes with them....

[puntloos]

2 minutes ago, Nickfromwales said:

Depends whether or not they brought their Peleton bikes with them....

700W in that case

 

[Nickfromwales]

9 minutes ago, puntloos said:

700W in that case

 

 

 

Jesus! His thighs are like Kim Kardashians arse cheeks!!!!! You could open a beer bottle between those.

[ProDave]

Christ on a bike.

[SteamyTea]

11 hours ago, puntloos said:

700W in that case

And 0.021 kWh of energy.

Can see why we use gas and electric.

[Nickfromwales]

11 hours ago, ProDave said:

Christ on a bike.

Yup. He’s better hope the Colonel doesn’t spot those, or they’ll be coated in 11 secret herbs & spices and straight in the deep fat fryer