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Unvented or vented ?


ToughButterCup
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Are you over complicating this for the application?

 

I would fit one of these https://www.hyco.co.uk/products/hot-water/speedflow

 

They are supplied with an over pressure relief valve that must be connected to a drain (no mention in the instructions of a tundish?)

 

And under some circumstances it may need an external expansion vessel.

 

I know of at least 2 of these in use in an office environment with the one heater feeding the sink in the kitchen and the wash hand basin in the toilet.  It sounds perfect for your application.

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8 minutes ago, ProDave said:

I would fit one of these https://www.hyco.co.uk/products/hot-water/speedflow

 

They are supplied with an over pressure relief valve that must be connected to a drain (no mention in the instructions of a tundish?)

 

Agree this is the sort of device but wouldn't recommend that brand... Look at the Stiebel Eltron Compact water heaters

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Just to be clear, Part G3 does not apply to unvented water heaters that have a volume of less than 15 litres, so the small under-sink units don't need all the complex stuff that a large unvented hot water tank will need.  This may include the requirement for a tundish to be waived, although manufacturers instructions (MIs) over-ride the requirements of Part G.  For example, our under-unit unvented water boiler (for the boiling water tap) is well under 15 litres, yet has to be installed with a pressure relief valve and a tundish to the discharge pipe, as it's in the MIs.

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26 minutes ago, JSHarris said:

Just to be clear, Part G3 does not apply to unvented water heaters that have a volume of less than 15 litres, so the small under-sink units don't need all the complex stuff that a large unvented hot water tank will need.  [...]

 

Thank you so much. 

( Edited to add for completeness: Approved Document  G3, 3.19

Water heaters with a capacity of 15 litres or less that have appropriate safety devices for temperature and pressure will generally satisfy the requirement set out in G3(3).

Building Regulatiopns 2010 Approved Document G, page 21.)

28 minutes ago, PeterW said:

[...] Look at the Stiebel Eltron Compact water heaters

 

Are you in the least surprised that I've ended up salivating over their kit?

The only little alarm bell going off in my head is a comment I remember J making (years ago: ebuild?)  about what Stiebel refer to as

'.... temperature raised by 25 C ... '

In other words I need to satisfy myself that a cold-only supply will suffice.

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Do not neglect the likely lack of pressure in a vented system needs to be factored in as the pressure & Flow rate is all about how high the main volume of stored cold (That keeps the tank pressurised) water is above the outlet point. In such systems this usually means that the flow rate to the upstairs shower is working from only a meter or so of head pressure.  It is this feature (drawback) that makes unvented systems and power showers so much more 'end user' friendly EG great flow rates everywhere and similar flow rates on both hot, including those locally generated, and cold flows around the house based on mains pressure albeit regulated.

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4 minutes ago, MikeSharp01 said:

 It is this feature (drawback) that makes unvented systems and power showers so much more 'end user' friendly

I just fitted a cheap (£100) shower pump to my vented system.

Been working fine since 2008.  One day I shall have a look at the little strainers on it.

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If normal life of sunamp heating element is 2-3 years and the unit  its costs over £1000 --then that does not sound like a good deal for a std type dhw system -other than it takes less physical space .still a long way to go before it could take over from std dhw system for majority of houses

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5 minutes ago, scottishjohn said:

If normal life of sunamp heating element is 2-3 years and the unit  its costs over £1000 --then that does not sound like a good deal for a std type dhw system -other than it takes less physical space .still a long way to go before it could take over from std dhw system for majority of houses

 

The heating element issue is the now-obsolete Sunamp PV, which has a tiny 2.8 kW element inside a small tube in a water heating circuit.  The heating elements in the current Sunamp UniQ range are much larger and run directly in the PCM.

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Just now, dimpsy said:

Is the element in the Sunamp UniQ replaceable?

 

No, apparently it isn't.  It's a concern that's been raised already, but Sunamp reckon that the element will last for the life of the unit, perhaps because it's relatively large and runs at a fairly low temperature.

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13 minutes ago, JSHarris said:

 

No, apparently it isn't.  It's a concern that's been raised already, but Sunamp reckon that the element will last for the life of the unit, perhaps because it's relatively large and runs at a fairly low temperature.

That would be a big worry for me.  What happens after the guarantee has expired if the heater fails?  You won't be happy if you have to scrap the whole thing,  I suspect you will be looking for a way to change it yourself?

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2 minutes ago, ProDave said:

That would be a big worry for me.  What happens after the guarantee has expired if the heater fails?  You won't be happy if you have to scrap the whole thing,  I suspect you will be looking for a way to change it yourself?

 

Changing the heating element means heating up the PCM somehow and draining it out of the battery, as the element(s) would be embedded in cooled, solid, PCM.  Sunamp reckon the elements just can't be changed, and the whole unit has to go back to them for replacement.

 

If it happens, then I'll definitely be looking at a way to try and replace the element(s) myself, but until then I'll just be keeping my fingers crossed that there's not a problem.

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5 minutes ago, JSHarris said:

 

Changing the heating element means heating up the PCM somehow and draining it out of the battery, as the element(s) would be embedded in cooled, solid, PCM.  Sunamp reckon the elements just can't be changed, and the whole unit has to go back to them for replacement.

 

If it happens, then I'll definitely be looking at a way to try and replace the element(s) myself, but until then I'll just be keeping my fingers crossed that there's not a problem.

Invert the unit so the heater is at the top, and apply a blowlamp to the area around the element would be my line of attack.

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2 minutes ago, ProDave said:

Invert the unit so the heater is at the top, and apply a blowlamp to the area around the element would be my line of attack.

 

Might well work, but it'd need something more gentle than a blow lamp, as the battery case is made from what looks like red HDPE.

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I have never been against the idea of the sunamp  and wonder if there is not a way to use the water heated type to better effect ,and keep your pv gen for other things .

@JSHarris 

do you havve the total amount of heat required  for your winter heating .

my thoughts are maybe a very large sunamp --charged in summer by solar thermal and  used for the winter,cos its no problem getting loads of heat in the summer months ,but heat loss in big tank and cost of suitably large tank are the killers to this idea

 

As i undestand it there is virtually NO heat los from PCM-- so ideal for long term storage -also it takes up less space than water storage ,and of course the solar thermal still does work outside the summer months ,just not as good .but cost of panels  is cheaper than a huge storage tank

 so the question is how much heat would YOU need to store for your house .

to use this as a good example of well insulted house .

controlling the heat from the panels is pretty easy on pump speed alone -faster means more flow/ less temp and vice versa --which is what i did with my much simpler  system to get best heat 

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21 minutes ago, scottishjohn said:

As i undestand it there is virtually NO heat los from PCM-

 

Some have the notion that the PCM in a Sunamp is like that in a hand warmer where heat is stored by the phase change but the material then sits at ambient temperature. I've not seen any evidence to support this notion and don't think it's true because it appears that once a hand warmer has a few particles change state (solidify) they act as a seed to spread the phase change to the rest of the contents. In other words, they're either fully liquid or (on the way to being) fully solid whereas the Sunamp can clearly sit in part liquid, part solid states and therefore must be at around the phase-change temperature to keep the liquid bits liquid.

 

So, I think it's likely there is a continuous loss from the PCM, just quite a lot less than from even a well insulated tank of water storing the same amount of energy mainly because the volume is smaller so the surface area can be smaller which means a) directly less loss and b) more effective insulation (vacuum panels) are affordable.

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3 minutes ago, Ed Davies said:

 

Some have the notion that the PCM in a Sunamp is like that in a hand warmer where heat is stored by the phase change but the material then sits at ambient temperature. I've not seen any evidence to support this notion and don't think it's true because it appears that once a hand warmer has a few particles change state (solidify) they act as a seed to spread the phase change to the rest of the contents. In other words, they're either fully liquid or (on the way to being) fully solid whereas the Sunamp can clearly sit in part liquid, part solid states and therefore must be at around the phase-change temperature to keep the liquid bits liquid.

 

So, I think it's likely there is a continuous loss from the PCM, just quite a lot less than from even a well insulated tank of water storing the same amount of energy mainly because the volume is smaller so the surface area can be smaller which means a) directly less loss and b) more effective insulation (vacuum panels) are affordable.

If loss is low enough then 5" of phonelic foam around it ,or the room its in  will make it as low as economically  possible-- above 5" the cost outwieghs any extra insulation value

Edited by scottishjohn
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38 minutes ago, scottishjohn said:

I have never been against the idea of the sunamp  and wonder if there is not a way to use the water heated type to better effect ,and keep your pv gen for other things .

@JSHarris 

do you havve the total amount of heat required  for your winter heating .

my thoughts are maybe a very large sunamp --charged in summer by solar thermal and  used for the winter,cos its no problem getting loads of heat in the summer months ,but heat loss in big tank and cost of suitably large tank are the killers to this idea

 

As i undestand it there is virtually NO heat los from PCM-- so ideal for long term storage -also it takes up less space than water storage ,and of course the solar thermal still does work outside the summer months ,just not as good .but cost of panels  is cheaper than a huge storage tank

 so the question is how much heat would YOU need to store for your house .

to use this as a good example of well insulted house .

controlling the heat from the panels is pretty easy on pump speed alone -faster means more flow/ less temp and vice versa --which is what i did with my much simpler  system to get best heat 

 

The total heating demand is around 1,600 kWh per year.  That would need a Sunamp that's around 178 times larger than the one we have, plus a bit to allow for losses that may not contribute to heating the house.

 

5 minutes ago, Ed Davies said:

 

Some have the notion that the PCM in a Sunamp is like that in a hand warmer where heat is stored by the phase change but the material then sits at ambient temperature. I've not seen any evidence to support this notion and don't think it's true because it appears that once a hand warmer has a few particles change state (solidify) they act as a seed to spread the phase change to the rest of the contents. In other words, they're either fully liquid or (on the way to being) fully solid whereas the Sunamp can clearly sit in part liquid, part solid states and therefore must be at around the phase-change temperature to keep the liquid bits liquid.

 

So, I think it's likely there is a continuous loss from the PCM, just quite a lot less than from even a well insulated tank of water storing the same amount of energy mainly because the volume is smaller so the surface area can be smaller which means a) directly less loss and b) more effective insulation (vacuum panels) are affordable.

 

Part of the "secret source" in the Sunamp PCM seems to be the way that it's been tuned to start and stop the crystallisation process.  As I understand it, the PCM does sit at around the 58°C phase transition temperature, though, so does lose heat at a fairly steady rate.  The heat loss from our 9 kWh unit is around 700 Wh/24h IIRC.  The insulation is vacuum panels, so a lot better than just any reasonable foam insulation.

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maybe I talk to sunamp and see how large a unit they are going to make and cost ?

 no maybe that won,t work as i think i remember you saying your 9kw unit weighs 150kg

even if i went for half that storage ,co there will be usable heat outside and partial recharging through out the year 

but even 50%would be  8 x150 kg 

 

Edited by scottishjohn
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