Solar iboost installation

zeupater

1961Nick wrote: »

I understand what you are saying but (you knew there'd be a but:)) I still think I can increase the total amount of energy stored in the cylinder with a destrat pump. It's a tall tank & there's a significant temperature gradient between the top & bottom. I've not measured it as yet but it's cool enough to touch the bottom but not at the top for very long. I know that's not very scientific but it's a starting point. It would probably only require a tiny pump to de-stratify it.

My purpose in this instance is not to reduce energy consumption but to look at ways to use green energy rather than gas for as much of the DHW as possible. Solar iboost is clearly a reasonably cheap way of doing this. A destrat pump is a potential add on if there's still a significant amount of surplus pv energy. I do accept your point that it would be 'greener' to export that energy & use less DHW. I confess to not being ethical in that respect but surely still qualify on the other two criteria?:)

Your mention of the boundary layer is interesting & a thermal map of the cylinder would be a sensible next step.

Hi

As soon as you draw any DHW an equivalent volume of cold water will enter the bottom of the cylinder therefore the bottom will always be cooler than the top. Regarding "there's a significant temperature gradient between the top & bottom" ... no, that's not the way stratification works - there's hot water, a boundary layer with a massive temperature gradient over a couple of inches, then cold water ... of course the boundary will eventually break down (it actually expands), but this takes a number of days ...

Our DHW cylinder is heavily insulated (solar spec) and has very few places where you can feel the temperature ... there's a little exposed metal on the immersion & coil connectors and that's about it. However, I have thermostats at 3 points and constantly monitor/display the readings digitally, but in addition I have an infrared remote digital thermostat which allows the accurate measurement of any spot-point in the DHW system or locate coldspots/draughts etc which does register temperature differentials over the surface of an insulated cylinder which you could not do by touch due to heat transfer to an insulating surface ....

To use a destrat pump efficiently you'll be better having separate access points into the cylinder, if not make sure that the plumber knows what they're doing or you'll risk introducing an additional point of heat-loss ... if you have an unvented DHW system don't even think of doing it yourself, but I'm sure that you're aware why ....

One of the main reasons that you normally see mention of de-stratification is due to the length of a top-fitted immersion coil. Many of these are very short and are only supposed to provide top-up heating. Some go down the expensive solution of adding a new circuit, whilst others simply get a long 3kW replacement immersion heater, or even one made bespoke ... someone on these boards had one made as a solution to your problem some time ago (12 mths ?) and it wasn't that expensive (£50 ish), so a little time searching existing posts may provide useful .... you might even find that they've been following this thread and appear with details - you never know ....

HTH
Z

1961Nick

I did think about a longer immersion heater but was slightly concerned about it touching the coil. Is there any reason for that concern?

I'd do the plumbing work myself so this project would amount to the cost of a small pump & a couple of tank flanges....the bottom one might be a !!!!!! to fit though! Yes it's an open vented system.

The house is empty during the week so the theory is to get as much free energy into the cylinder as possible ready for the evening. It may be that this is primarily achieved with just the solar iboost. Monitoring will obviously answer that question.

Finding out where the boundary layer is will hopefully give some indication of the tank's potential.

zeupater

1961Nick wrote: »

I did think about a longer immersion heater but was slightly concerned about it touching the coil. Is there any reason for that concern?

I'd do the plumbing work myself so this project would amount to the cost of a small pump & a couple of tank flanges....the bottom one might be a !!!!!! to fit though! Yes it's an open vented system.

The house is empty during the week so the theory is to get as much free energy into the cylinder as possible ready for the evening. It may be that this is primarily achieved with just the solar iboost. Monitoring will obviously answer that question.

Finding out where the boundary layer is will hopefully give some indication of the tank's potential.

Hi

The boundary layer will be around the lowest heated level in the cylinder when fully heated, therefore the potential would be the volume of water in the stack above that .... the maximum potential would therefore be the capacity of the tank, if the heater was long enough .... as you draw DHW, the boundary layer simply moves up the tank due to cold feed water displacing hot, however, you'll not achieve true stratification unless the heating element delivers the majority of the energy as low in the cylinder as possible ...

Whichever way you go - what's the size/capacity of the current cylinder ?

HTH
Z

1961Nick

zeupater wrote: »

Hi

Whichever way you go - what's the size/capacity of the current cylinder ?

HTH
Z

Hi Z,

The tank is 1.2m tall & 162 litres capacity.

Now I've had a good look at it, I've decided it's going to be too difficult to fit the bottom flange without removing the tank from the cupboard.

zeupater

1961Nick wrote: »

Hi Z,

The tank is 1.2m tall & 162 litres capacity.

Now I've had a good look at it, I've decided it's going to be too difficult to fit the bottom flange without removing the tank from the cupboard.

Hi

Not large then, about 9kWh to heat to 60C from cold .... you could increase the storage by turning the thermostat up a little, but don't do this without a whole-house TMV in place or if the cylinder is old. As suspected, 110Tonnes of 60C DHW would need the equivalent of 2 complete heat cycles/day probably by being very careful with the timer, but the boiler would need to be used every day, even in summer ...

Think about it ... if 100Tonnes are used by the shower and all showers are in the morning, then the boiler would need to be set to work in the morning, else you'd simply run the tank cold - but, as soon as there's enough DHW for the last shower the boiler must be set to cut out immediately, or you'll have a full tank of hot water and not be able to collect much from the pv .... the best (most logical) solution would be to have the timer set to not heat during the day, collect whatever you can from pv, set the timer to come on late afternoon/evening, time your daily schedule to timer on/heat/shower/heat/timer off/shower at a specific (pretty exact) times in the evening, which will at least leave room for some pv heat diversion the following day, but not being in during the day with a small cylinder and atypically high usage leaves little 'wiggle room' to shoehorn heat in ... if you're lucky you might get 5kWh of top-up from the pv even on the best of generation days, but probably not much more whatever you do ....

The answer's a much bigger cylinder (300l+), reduced DHW consumption ... and/or a re-evaluation of the volume of the volume of DHW which is currently being used ...

HTH
Z

1961Nick

The tank stat is already set at 70C just to cope with 3 showers within the space of 45 minutes in the morning! Even that's marginal for the last showerer.

Your thoughts on the timing of the boiler cut out are similar to mine.

I looked into that possibility of installing a larger tank some time ago but unfortunately the airing cupboard won't accommodate a larger one. Raising the temperature was the only option without compromising the showers.

Estwing

Will you just buy the bloody destrat pump please :eek:

Then let us know how's it doing, as I'm thinking of getting one:rotfl:

(Similar problem)

Dave_Fowler

Estwing wrote: »

Will you just buy the bloody destrat pump please :eek:

Then let us know how's it doing, as I'm thinking of getting one:rotfl:

(Similar problem)

I've fitted a de-strat pump - it was quite easy. Connected it between the hot water output from the tank to the cold water input (from the header tank). I fitted a non-return valve in line with the pump so that water could only flow from the hot side to the cold side. Took less than an hour to complete. The pump is operated when the immersion thermostat opens when the preset maximum temperature is reached. I find that the de-strat pump operates three or four times before all the tank is at maximum temperature.

Dave F

1961Nick

Estwing wrote: »

Will you just buy the bloody destrat pump please :eek:

Then let us know how's it doing, as I'm thinking of getting one:rotfl:

(Similar problem)

LOL

Too busy replying to Z to actually fit one!:)

1961Nick

Dave_Fowler wrote: »

I've fitted a de-strat pump - it was quite easy. Connected it between the hot water output from the tank to the cold water input (from the header tank). I fitted a non-return valve in line with the pump so that water could only flow from the hot side to the cold side. Took less than an hour to complete. The pump is operated when the immersion thermostat opens when the preset maximum temperature is reached. I find that the de-strat pump operates three or four times before all the tank is at maximum temperature.

Dave F

I'd be interested to know what pump you used. I've searched the wed & can't seem to find anything small & sensibly priced.

Once your tank reaches maximum temperature, does the pump run continuously?

Unfortunately the cold feed to my tank is round the back with absolutely no access.