Charging a sunamp stack in winter

[dnoble]

Good morning  

I'm building a passive standard MBC house and planning the hot water.

I had planned to have a large thermal store heated with solar thermal in summer and backboiler off a wood-burner in winter.

Going to have 4kw PV system on a SW facing roof which presumably wont provide much help in winter.

Having read of Jeremy's travails with heat loss and overheating I think a sunamp stack would be a better way to go (have 4 children who occasionally take showers and may at some point wash regularly)

Speaking to the sunamp guy, Andy, it seems relatively straightforward to charge it from a backboiler on a woodburner.

However I'm beginning to get the impression that a woodburner probably isn't the best fit for a passive house (overheating, cold bridges with chimney and direct air inlet) and the Neanderthal in me is (very) reluctantly thinking if letting this idea go.

So...

 

1) Does anyone think a woodburning in a passive  house is a viable way to charge DHW in winter (I have access to a lot of wood btw)

I think there may be some models which direct most of heat to back boiler and I could also send some to UFHS via the sunamp

 

2) If not am I stuck with charging the sunamp in winter using mains electric/E7 etc (I don't really want to get a GSHP or connect to mains gas)

 

Best wishes

Dan

 

[Nickfromwales]

Ashp ?

That with a large UVC seems a no brainer, coupled with a buffer and just drive the Ufh direct. 

Re the wood burning stove ( WBS ), you can have one with a ph, just fit it outside . Why build an airtight low loss house and then stick a chimney in it ? ?

With 6 of you consuming DHW I seriously doubt that the SA stack would be the best choice. Pump all the Pv into the UVC, and the winter won't be a problem you just boost off E7 / grid as necessary. 

 

Check out @Stones blog. He's getting some really good numbers back off his ashp. 

[Guest Alphonsox]

We use E7 to charge ours all year round. It makes a good match imho. We had intended to use PV as well but this doesn't currently look very attractive given the current market in our part of the world.

[Jeremy Harris]

One major problem with a wood burner is finding one small enough.  Some people that came to look at our build had completed a passive house and fitted the smallest room-sealed wood burner they could find, one intended originally for use on narrow boats, I believe.  The lit it for the first time at Christmas, when they had a family gathering.  Within an hour the living room was well over 30 deg C and they had to open all the windows.  The room continued to remain hot so they had to abandon it, leaving the windows open and retire to another room.  They couldn't get back in the living room until the next day, when it had cooled down enough to be bearable.

 

When I last spoke to the lady she was in the process of sealing off the wood burner flue and underfloor air feed duct and fitting an LCD screen inside it to make it look as if it was working.  I did a few quick sums for her, and on the day in question her living room would have needed around 300W to maintain 21 deg C.  There were four people in the room, that would have provided around the 300W needed, and the small stove was rated at 3 kW.  So, when they lit it, they were putting in around 10 times more heat than the room needed, potentially enough to heat the room to a very high temperature had they not opened the windows (it could have probably got to around 50 to 60 deg C I think).

 

I agree with the comments above.  Our Sunamp PV is charged by excess solar generation around 70% or more of the time, but I have a two hour timed boost that comes on at 4 am, to make sure that it is fully charged first thing in the morning, no matter what the PV output was like the day before.  The cost of doing this is small, especially if you're on an E7 tariff.  Likewise, you can boost the Sunamp at any time using a boost timer, just like an immersion, if need be.

[le-cerveau]

I am installing a SunAmp Stack, but a bespoke one with dual temperature cells:

The Low temp cells will be charged from the ASHP whilst the high temp ones from the boiler (I have mains gas).

This allows mem to take the best of the high CoP from the ASHP for both UFH and DHW pre heat, the High temp (normal) cells will provide the boost.  This is for a 5½ bed house allowing for 3 concurrent 12 l/m showers, and the capacity for fill a stupidly large bath.

The diagram is the latest from SunAmp, they are building it at the moment, final details will be known in the near future.

[Barney12]

34 minutes ago, le-cerveau said:

I am installing a SunAmp Stack, but a bespoke one with dual temperature cells:

The Low temp cells will be charged from the ASHP whilst the high temp ones from the boiler (I have mains gas).

This allows mem to take the best of the high CoP from the ASHP for both UFH and DHW pre heat, the High temp (normal) cells will provide the boost.  This is for a 5½ bed house allowing for 3 concurrent 12 l/m showers, and the capacity for fill a stupidly large bath.

The diagram is the latest from SunAmp, they are building it at the moment, final details will be known in the near future.

 

Thats interesting. When I asked Sunamp if using as a heat source for UFH they said that it wasn't recommended? Perhaps though that's jus the case for the 'standard' units.

[Jeremy Harris]

1 hour ago, Barney12 said:

 

Thats interesting. When I asked Sunamp if using as a heat source for UFH they said that it wasn't recommended? Perhaps though that's jus the case for the 'standard' units.

 

 

Yes, the standard cells use the PCM 58 material, which runs at around 58 deg C, the newer material is PCM 34, that runs at around 34 deg C, and is better suited to UFH.  The Sunamp PV uses the PCM 58 material, AFAIK, hence the earlier comments about it not being best suited for use with UFH.

 

One option that I may well consider in future is to replace our buffer tank with a Sunamp Stack fitted with PCM 34 cells.  That would be charged via the ASHP and provide both DHW preheat and UFH buffering.  The big advantage is that I could get around 3 times the thermal storage capacity in the existing space, which would be a very useful benefit.

Edited September 3, 2017 by JSHarris

[dnoble]

Thanks for all the replies.

It does seem that a woodburner would be an unwise extravagance. I'll have stick to bonfires

I hadn't considered adding an ASHP also. Would this be to pre-heat the water so the stack needed to do less work, or will it actually directly charge the stack (presumably using less electricity). 

Any recommendations for ASHP type and price?

[le-cerveau]

On ‎03‎/‎09‎/‎2017 at 12:56, JSHarris said:

One option that I may well consider in future is to replace our buffer tank with a Sunamp Stack fitted with PCM 34 cells.

 

The big issue is hydraulic separation between potable and non-potable water.  My setup keeps the water in the cells potable and uses PHE's to charge and take out the UFH circuit, for your setup if you keep the cell as non-potable you only need one PHE for your DHW, but loose the instant slug of warmer water, otherwise you will need 2 x PHE, one for ASHP charging and one for UFH take off.

[Jeremy Harris]

15 minutes ago, le-cerveau said:

 

The big issue is hydraulic separation between potable and non-potable water.  My setup keeps the water in the cells potable and uses PHE's to charge and take out the UFH circuit, for your setup if you keep the cell as non-potable you only need one PHE for your DHW, but loose the instant slug of warmer water, otherwise you will need 2 x PHE, one for ASHP charging and one for UFH take off.

 

 

My existing system uses a PHE upstairs, with the buffer downstairs, and the PHE is always pre-heated by thermosyphon action, so I would guess the same would be true if I just swapped the buffer tank out for a Sunamp Stack fitted with PCM 38 cells.

[le-cerveau]

I have had an update from SunAmp who will now supply my equipment based on the new Dual Port (??) more when I know about it however here is the latest schematic.

[dogman]

@le-cerveau based on your posts i went back to Sunamp as I was going for two PV's. They sent me information on the new dual port but it will not be available till Q1 next year which is no good for me.

Is your option the new Dual port or stack built to work like a the new dual port