ACV Smartline 240

[Lesgrandepotato]

Looking at ordering one of these up shortly. House is UFH all the way through. 1970's build with 60mm internal insulation all over, triple glazing and loft and slab insulation. So it's insulated to a modest standard nothing more. This ain't no passivehause!

 

Build has 8 zones of heating and circa 2800sqft of living space with a couple of 5kw wood burners. 

Plan is to use the existing condensing 37kw oil boiler as a primary heat source, later down the line we'll look at some micro hydro from the millstream as a backstop (thinking circa 2k continuous) we can then augment with an ASHP or similar if we want / need to. 

 

Any thoughts? 

Edited August 6, 2017 by Nickfromwales
Link added ?

[Nickfromwales]

Eg 1

Eg 2

A bit expensive, and I'm not all that convinced with the whole 'tank in tank' necessity TBH. Why not a cheaper straight forward TS? 

 

[Lesgrandepotato]

Hmm. That's the one. The quotes I've had for other tanks have been significantly more expensive! What should I be paying?

[PeterW]

Had one and took it out from a commercial set up. 

 

It was on an ASHP set up and it wasn't great - watch the actual volume of the tank as the 210

relates to the external tank size and I think the inner tank

takes a good 40/50 litres out of that.  

 

If you have oil then a big UVC, or get Newark to make you a custom TS that you can shove a couple of immersions into a diversion loads from the hydro. 

[Nickfromwales]

3 hours ago, Lesgrandepotato said:

Hmm. That's the one. The quotes I've had for other tanks have been significantly more expensive! What should I be paying?

For comparison, the last 500ltr TS with a  46kw DHW coil came in for change of £1150 ish. 

[Lesgrandepotato]

Ok. So assuming the 240l can take the heat load without being always emptied, and I believe it can then if I can get it for around 950ish it's a reasonable deal given it's off the shelf instead of bespoke? 

[PeterW]

240 is not a lot of stored water - how many showers etc ..?

[Lesgrandepotato]

Two showers, one in regular use. Family of three in residence. Two adults one small boy 

[Lesgrandepotato]

The specs suggest it'll do around 913L in an hour at 60c. (1st hour) and 272l @ 60c in the first 10mins. That should run the bath and a shower at the same time? 

 

[PeterW]

That is assuming the boiler can keep up - there is only 164 litres of water in there and the tank in tank is half the size of a standard coil in a Telford UVC which would have 50% more water in it. 

 

Any reason for the TS..??

[Lesgrandepotato]

Yep. Plan is to take a circa 3kw feed from a pelton wheel from the millstream and run as 'dirty' electric into the immersion element.  Boiler is rated at 37kw, I'm hoping/expecting that by buffering in a TS we'll get the best out of the boiler feeding the DHW and UFH as it'll get to run a decent burn and condense properly. 

[Lesgrandepotato]

Why are there only 164 litre of water in it? There is a 240l total capacity, with two tanks. 

 

Assuming for now that the tank is hot that's 240l of water at 80C, we take out say 10l @ 60c, that will need to be replenished into the store. That would be the same for tank in tank as opposed to coiled heat exchanger? I guess the advantage is simplicity of build and no change of scaling up the heat exchanger?

 

in my mind 240l of tank in tank is the same stored heat as 240l of single tank with heat exchanger? It's still 240 l of water @ 80c? 

 

Confused of Cumbria!  

[PeterW]

164 litres of usable DHW.  The other 80 is the heat exchanger contents which is incredibly poor in its design. The "descaling" is basically the ribbed internal tank expanding and contracting and then the scale cracks away. Ours had a lot of scale in the bottom of the outer tank. 

 

Newark do a copper TS off the shelf with a big mains pressure coil. http://www.newarkcoppercylinder.co.uk/thermalstore.html

 

I would question if the ACV doesn't need a G3 ticket as the outer is a pressure vessel - for that sort of money you could get a 250 litre UVC and a buffer and get the best of both worlds. 

 

 

 

 

[Nickfromwales]

Any cylinder holding stored, heated water that is sealed and pressurised, needs G3. A combination aka open pipe TS does not. 

Im a Telford man, and I prefer the fact that they make theirs out of all stainless steel. As far as bespoke goes, Telford manufacture to each order using their basic dumb cylinders as the base for each order. The cylinders are off the shelf but you can specify where the tappings go, within practicable reason, at no extra cost. Turnaround time is still less than a week from placing the order iirc. I see zero benefit from the tank in tank ( TIT for short ? ) option, with its reduced capacity for the same size cylinder. 

 

Id only go for the two tank UVC + buffer option if there was an ashp involved. With a 37kw oil boiler I'd be really worried about such a small second vessel as the oil boiler performs best when allowed to do a long burn at full wallop, rather than cycling in short bursts, and would reheat a 100L buffer very quickly indeed. I'd go for a single cylinder stat to stretch out the hysteresis of the on / off cycle to further promote this. 

[PeterW]

+1 to what Welsh pieboy says - Telford turned around my 500 litre UVC in less than 72 hours. 

 

You can go open vent TS (I had a Newark one in the last place) and they are fantastic but copper is expensive ...!

[Nickfromwales]

Telford vs Newark eh? There's only one way to settle this............

 

 

 

 

[Nickfromwales]

36 minutes ago, PeterW said:

You can go open vent TS (I had a Newark one in the last place) and they are fantastic but copper is expensive ...!

Only real negative is the extra heat loss from having this open to atmosphere. @JSHarris' blog highlights this in detail. 

[Jeremy Harris]

Yes, I can confirm that the heat loss from our old 210 litre combination thermal store was far too high for us, so high that it cracked the oak door between the services room and the adjacent bedroom.  The services room would easily get to over 40 deg C on a warm day, with almost all of that heat coming from the thermal store, even after I'd added an extra layer of insulation, by bonding on a 50mm layer of PIR foam all around the thermal store.

[Lesgrandepotato]

Right spoke to Telford and a recommended reseller. 

 

They have said the following 

Presssured Mains Coil,

2 Immersions

Direct Output (no buffer)

Mains DHW coil in the top

 

They have suggest going for 300L + Unvented but they have no view of the size that we could be requiring. 

 

Does anyone have any science about sizing these? Or should I just see how big the space is and buy big? We think 3/5kw should be possible from the Pico hydro setup

 

[Nickfromwales]

The hydro set up makes me think you should go bigger. Do you have any info regarding expected yield, eg pattern of delivery for the hydro ? Can we assume the hydro will give 3kw idle and 5kw peak, with 3kw a fairly constant ( over 24hrs ) figure? 

If the 3kw is a constant, then I'd say much bigger. I'd want to harvest as much of the hydro generated energy, convert it into heat energy in the TS, and have it stored ready to be used to off-set the shunt heating load, eg when the house is asked to attain the target / comfort temp, plus DHW. To do that in a TS of say 300L capacity would be IMO a stretch. I'd go for ~800L, more if the space is there, but that is wholly dependant on the hydro figure being accurate. You stated 2kw in the OP but now your saying 3-5kw, so have you had some feedback from the unit installers ? Also, can they provide an excess generation controller ( hydro equivalent of the Immersun ) that will pump excess into the second immersion ? If not, make sure one of the immersions is a 6kw, and the second at least a 3kw so you have 9-12kw of electrical boost ( also a backup if the oil ever runs out and you need to temporarily switch to electricity to keep things running ). 

Id deffo want to design this so the hydro is providing the maximum yield, and that is best achieved by using it to trickle charge a large heat battery, aka TS. 

[Lesgrandepotato]

I've had a word with the hydro designer - he's not sure on the detail as he's never designed one before. But he has a relevant degree and a sense of adventure. So frankly I don't know how I'm going to spec it up yet :-)  but I have a beck, a culvert and a poorly thought through plan! 

 

it appears the peak load of the heating is 14.8kw, so that would suggest an approx 30% duty cycle for the boiler at full tilt hearing. Presumably though for the majority it's going to be significantly below that so perhaps a 5kw background load? Does anyone have a figure on the normal duty cycle of UFH in a regularly insulated building? That would suggest it's running around 30% capacity all the time. So this does suggest that will a bit of work then the hydro should be able to manage the heat load in the shoulder months and summer and we could top up with the two log burners (5kw) each to heat from stone cold? 

 

Who can point out the flaws in my logic? Assuming it all holds then if we assume a say 90% efficency on the store then we can work out the amount of energy we need to store and the potential duty cycles...

[SteamyTea]

You can search for the nearest gauging station (if your river is on it) here.

https://nrfa.ceh.ac.uk/data/search

[Nickfromwales]

Continued from my comment here to keep that thread on topic. 

 

Having the bigger TS, even part satisfied and storing at lower temp, would still give plenty of DHW and low grade space heating energy, so the excess hydro would only have to be dumped after that achieves 80-85oC. Then, and only then would I worry about diverting to things like the towel rads, but tbh I'd run them off a separate low temp wet manifold, as well as the electrical element for backup, ( so oil can take over for generation-shy periods or all out failure / servicing of the hydro ), and keep all the services running as normal.  

@A_L has given a great solution, but mine utilises just about every ounce and provides a means to store it usefully, rather than dump it. 

Dont just think of DHW from the hydro, it can also proved an offset for space heating too, if your insulated and reasonably well enough to run a low temp heating system. Mvhr would further reinforce this solution. The oil boiler should only kick in to bridge any gaps / top up the cylinder with the cyl stat set at around 55-60oC. 

@Lesgrandepotato, remind us that you are also on grid electricity ? And size of supply ?

[Lesgrandepotato]

Hi Nick, plan is to offset space heating as well, we'll also have the levels of control to try and 'preload' the slab overnight with an excess of temp (if needed).

 

Towel rails will be dry - to late to become wet! . We are on grid electric - not sure on supply size but we are on the outer reaches, think there is a substation on a pole involved upstream somewhere near the village. 

[SteamyTea]

Water is 4.2 kJ for 1°C temperature rise per litre of stored water, so 0.00117 kWh/kg.

Concrete is about 0.8 kJ per kg, so 0.00022 kWh/kg.

 

Knowing that, you can try and work out how large a water and slab store you need if you know the temperature bounds you want to keep the slab at.

In physics, most things want to be equal at the lowest energy difference.  So a thermal store only needs to be sized to cover the load, minus the temperature difference between the upper and lower temperature bounds of the slab.  Plus any thermal losses as well.

(I may have to revisit this to make it better English, but off to work now).

 

Edited August 16, 2017 by SteamyTea