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Trying to find a solution...


ZacP

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I’m trying to use a bit of insulated loft space for MVHR and Hot Water Cylinders rather then having to design in a plant room (other things like UFH manifold, fuse board etc. have other out of the way locations. 
 

Only issue is max head height is 1.2m. I’d ideally like to have 400L of hot water (planning for the day when my 2 daughters are teenagers). So...

 

- Is there a 400L or similar tank with a height of 1m (allowing for pitch)?

- can cylinders be mounted on their side or at an angle?

- can I have 2 smaller tanks in series or parallel? 
 

if these are ridiculous options let me know and I’ll go back to the drawing board and squeeze a plant room in!

 

thanks all!

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15 minutes ago, ProDave said:

What has drawn you to 400L?  What is your heat source?

ASHP and immersion for the 60deg boost. Might add PV at some point if and when we can afford it. 
I can’t remember why we thought 400 was suitable. Happy to be convinced otherwise!
its a 5 bed 3 bath. Certainly don’t want to be running out of hot water part way through a shower and with two daughters I can only imagine the hours they’ll spend with the shower on. 

Edited by ZacP
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Just now, PeterW said:

Two 200 litre horizontal tanks in series would work, downside is they don’t do a heat pump coil in the Telford ones unless you order it special and I think it’s quite a bit more expensive. 
 

 

Is that over spec’ing it do you think? Should we just go for a 300 and wait for the water to warm up again? What is the approx warm up time for a 300l cylinder from a ashp?

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My 300L tank and 5kW ASHP can take 90 minutes to heat from cold.  Re heat from partial depletion is ovbiously less. 

 

I "solved" the ran out of hot water and long re heat issue by fitting a 10kW modulating Steibel Eltron water heater in series with the output.  Normally it does nothing and the HW just passes through, but if the tank is depleted it takes over and at least gives you some hot water.  It has "saved the day" a few times.

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16 minutes ago, ProDave said:

My 300L tank and 5kW ASHP can take 90 minutes to heat from cold.  Re heat from partial depletion is ovbiously less. 

 

I "solved" the ran out of hot water and long re heat issue by fitting a 10kW modulating Steibel Eltron water heater in series with the output.  Normally it does nothing and the HW just passes through, but if the tank is depleted it takes over and at least gives you some hot water.  It has "saved the day" a few times.


I also have one of those “in stock” in case but not fitted yet, I have yet to run out of hot water but there is only two of us and few visitors (especially recently ?)

 

someone here was concerned the reduction in pipe diameter to 15mm would cause flow problems , @ProDave did you experience this?

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1 minute ago, joe90 said:


I also have one of those “in stock” in case but not fitted yet, I have yet to run out of hot water but there is only two of us and few visitors (especially recently ?)

 

someone here was concerned the reduction in pipe diameter to 15mm would cause flow problems , @ProDave did you experience this?

The times we have ran out of water is when both the ladies have showers in quick succession without re heat time between and when they are both hair wash showers that's when it can run out.  I measured the shower flow at >15L per minute on full flow so that's about half an hour to empty the tank.  Now I cannot personally imagine what one could do for 15 minutes in a shower, that's obviously a lady thing (with long hair)

 

I think if you add in the temperature probe in my tank is about 1/3 the way up the tank, so the tank could be only just over 2/3 full and it would not be calling for heat so you might only have 200L of hot water sitting there.  Perhaps a lesson from this is specify the thermostat pocket lower down?

 

As regards flow rate, no problems.  If I could do one thing differently, I would NOT have fitted full bore isolator valves on the showers, I would have fitted normal ones to slow the shower flow slightly.

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3 minutes ago, ProDave said:

the temperature probe in my tank is about 1/3 the way up the tank,


for some reason I have two pockets in my tank, one at 1/3 and one at 2/3, when we get visitors I move the stat to the lower pocket ?, I wonder why the lower one is not near the bottom of the tank to utilise the whole tank, no point in having a 300 litre tank if you cannot use it all!!!   Answers on a post card to.........

 

7 minutes ago, ProDave said:

As regards flow rate, no problems.


Good to hear.

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7 minutes ago, joe90 said:


for some reason I have two pockets in my tank, one at 1/3 and one at 2/3, when we get visitors I move the stat to the lower pocket ?, I wonder why the lower one is not near the bottom of the tank to utilise the whole tank, no point in having a 300 litre tank if you cannot use it all!!!   Answers on a post card to.........

 

As the tank is heating, the water gets stirred around by convection, so it will heat the whole tank to the required temperature.  The problem is as you draw water off, the water remains stratified and all that happens is the hot water moves up and cold comes in at the bottom to replace it.  It is not until the hot / cold transition reaches the thermostat that it calls for heat.

 

fitting the lower thermostat pocket at say 1/5 up the tank might be better?

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400litre (probably 500kgs+ with tank) 

 sounds like a lot of weight to put in a modern loft considering how skinny the roof trusses are 

make sure you can spread that load  and consider carefully where to put it --like on top of a stud wall in rooms below 

Edited by scottishjohn
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On 27/11/2020 at 21:16, ZacP said:

What is the approx warm up time for a 300l cylinder

All depends on how low you allow the temperature to drop, how high you want the temperature to rise and the power of the heat source.

 

So taking a 300 lt cylinder that has dropped to 32°C, and you want to raise it back up to 60°C (28°C rise).

 

4.2 [kJ.kg-1.K] x 300 [kg] x (60-32) [K] = 35,280 [kJ]

 

Multiply by 0.0002777 to convert to kWh

 

35,280 x 0.0002777 = 9.77 [kWh]

 

To calculate time to raise temperature, device by power of heat source.

If the heat source is 9 kW, then.

 

9.77 [kWh] / 9 [kW] = 1.1 [h]

 

 

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I’m still thinking tandem tanks here and having the second one with a boost immersion heater on the “just in case” scenario. It gives you flexibility in how you pipe stuff up, but essentially your priority is always tank 1, the last tank before the outlets. This can be set slightly higher temperature and has the priority on any solar PV etc. Tank 2 is then the tandem backup, but doesn’t matter if it is hot or cold. When there are less occupants then T2 isn’t used but is essentially a cold water buffer. In terms of controls it’s relatively simple to manage with a pair of tank stats and a switch to decide if you want 200/400l of hot water. 
 

A pair of 200 litre tanks spread across both sides of the attic space would be easier to handle too, but don’t forget you need to get them up there in their first place and they are not light..!!! 6x2 bearers across min 6 rafters is standard for this sort of load, if you can get it

bearing on top of a wall then that’s a bonus. 

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One other thing to keep in mind is 400L of (occasionally) 60°C water in a small space will create a very warm loft. I'm assuming it's a well insulated space anyway if you're planning to put the MVHR unit there too, but it may impact some other choices. Getting in to change the MVHR filter maybe a sweaty task!

( We put the cylinder and UFH manifold into our laundry room specifically so any escaped heat is useful for clothes drying, after reading that tip on here )

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ok so what is the smallest space you can have for a hot water cylinder and UFH manifold? Just weighing up the options! Loft may be useful for storage anyway.... just have to convince SWMBO to give up space in the utility room! 

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We're allowing 1500x700mm but using the 300L Geocoil UVC which is narrower than most. Probably could squeeze into slightly less space if really planning it out. (there's also showersave pipe and the immersion and ASHP controllers etc in that space)

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300 litre Telford Tempest with the Heat Pump coil is 1650mm tall x 554mm diameter. 
 

30 litre expansion mounted above it would need another 330mm in height but the whole lot will squeeze into a 600mm wide gap if you get them to put all the connections in the 10-2 zone on the front of the cylinder. If you really run tight on space then Advance do a rectangular buffer tank  if you need one for the UFH you can stand a UVC on

 

https://www.advanceappliances.co.uk/product/141-buffer-stores/


Advance may do you a deal on one of these with a UVC - they do a 300 litre tank with a 4sqm coil for slightly more which will heat quicker if you have a larger ASHP

 

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1 hour ago, PeterW said:

300 litre Telford Tempest with the Heat Pump coil is 1650mm tall x 554mm diameter. 
 

30 litre expansion mounted above it would need another 330mm in height but the whole lot will squeeze into a 600mm wide gap if you get them to put all the connections in the 10-2 zone on the front of the cylinder. Il for slightly more which will heat quicker if you have a larger ASHP

 

The expansion vessel can go next to the tank so no extra height needed.

 

But you do need a little bit of space above as the hot comes out of the top of the cylinder so you need room for an elbow and a bit of pipe plus insulation so say another 100mm?

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8 minutes ago, ProDave said:

The expansion vessel can go next to the tank so no extra height needed.

 

But you do need a little bit of space above as the hot comes out of the top of the cylinder so you need room for an elbow and a bit of pipe plus insulation so say another 100mm?


what I meant was you can stack this lot in a very small footprint - you can get 300 litre UVC and all its control set and expansion in a 600x650 space which is the width of a standard cabinet - it can go in a utility room full height cabinet door  width (minus one side of the frame usually) but is achievable. UFH manifolds can be hidden in walls as they aren’t that thick - 150mm depth if you swivel the pump round but it’s all perfectly doable. 

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So the utility is a standard 2400 high so plenty of height. Current design is 3.2m x 2.2m so think we could sacrifice 800mm or so to fit a 400L tank, manifolds, extension vessels etc. etc. So it would be a utility of 2.4m (4x600mm units) x 2.2m. Smaller then we hoped but might be more sensible then the loft?

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