PV and other alternative energy sources.

[dedee]

Roy,
Oh dear. Why will it not work?

To answer your questions.
The current water heater is made by Thermor and is heated electrically. It is made from steel. The heating element is a "stealite resistor housed in an enameled sheath". The tank has an enameled lining and the heat insulation is polyurethane foam. The insulation is very good. Even when at max temperature the outside of the tank does not even feel warm.
It is a 250l tank. and looks like this

I have written to Thermor about feeding heated water rather than cold into their appliance and am awaiting a reply.

The overnight venting (when it is heating the water) is perfectly normal. This type of water heater is very common here.

Thanks for your help, sorry if I am being a bit dim.

Cheers

Andy

 

[Digit]

From your drawings Andy you're not heating your DHW from solar panels, you are mixing the water. That precludes any idea of anti freeze and means water from the solar panels will only enter the DHW cylinder when water is drawn off and the approriate vales are opened/closed.
You need a heat exchanger inside the DHW cylinder.
I can't find any info on that make of cylinder, but in the UK bosses for fitting heat exchangers into cylinders after installation are available. They are available both as solder fittings and mechanical fix.

Roy.

 

[wobblycogs]

I read the plan as having a completly sealed solar heating loop heating a second hot water tank in line with the main hot water tank. Therefore the solar heating loop could contain anti-freeze as it never comes into contact with the water. I must admit I was confused about the use of a fancy coil in place of an immersion heater because it would be simpler to just buy a tank with a coil fitted.

The problem with this design is that hot water from the solar tank won't be drawn into the main tank until water is drawn from the main tank. This isn't as efficient as heating the main tank directly but it looks like it will work. An alternative solution would be to have a three port valve connecting the two outputs from the two tanks into the single hot feed for the house. When the sun is shining the valve would be set to draw water from the solar tank and in winter from the normal tank. You could even have a switch in the house to change the valve position.

 

[Digit]

You could even have a switch in the house to change the valve position.

:lol: :lol:

I did that with our CH. Due to surgery for prostate cancer the boiler commissioning was left to a local heating engineer.
I was in PJs, on a reclining chair with a catheter stuck in me me explaining for over an hour to this guy that the circuit was designed to allow DHW from the cylinder to be used at the taps if/when the boiler went US.
He went off muttering 'never seen anything like that before!'

Roy.

 

[dedee]

Wobblycogs ( can I call you graham? )

I think you have explained it better than me.

I understand what you are saying about the flow of solar heated water to the main water heater but being as most of our hot water is used after dark it means that the water heater will be filling up with solar heated water and hence will not have to work so hard to bring it up to temperature. The water heater BTW is only heating water from 10pm to 6am and although I've never measured it the water at the taps feels as hot at 9.30pm as it is at 6.30am.

You mentioned a tank with a coil already fitted. is this a heat exchanger type coil that I could connect to the solar panels? Could you give me an example?

I've have seen a couple of cylinders here that have an exchanger type coil in the bottom of the tank with a conventional heating element at the top - but they are VERY expensive.

Cheers

Andy

 

[wobblycogs]

Graham or Wobblycogs either is fine by me.

I wasn't actually aware that you could get hot water cylinders that didn't have a heat exchanger coil built in. Anyway, I was thinking of something like this http://www.heatandplumb.com/acatalog/Heatrae_Sadia_Hot_Water_Cylinders_Megaflo_HE.html. Megaflo is one of the best makes and is priced as such, you can get cylinders much cheaper than this.

The things to note though are the heat exchanging coil at the bottom of the tank, this is what you connect to your solar heating system. Cold water goes in at the bottom, and hot out the top of the tank as usual. Notice that the tank also has a built in expansion gap at the top. You can also get twin coil tanks which allow you to, for example, heat the top half of the tank with gas and the full tank with solar or the other way round (we have one of these but currently only use gas).

 

[dedee]

I wasn't actually aware that you could get hot water cylinders that didn't have a heat exchanger coil built in.

D'oh, can I have a senior moment at 47? Yes of course it's how the hot water from the boiler heats the water in the cylinder. All I'd be doing is swapping the boiler for the solar panels.

I'll spend time time over christmas doing some proper costings on this.

cheers

Andy

 

[Jake]

I haven't read the whole thread, so forgive me if I am way off base or repeating something already said, but heatbanks are ideal for this, rather than conventional cylinders.

 

[MikeG.]

Jake,

if I understand these things correctly, a thermal store is essentially a cylinder kept permanently full of hot water, with a second heat exchanger. This second heat exchanger (coil) takes the cold water feed (mains) and heats it for use at the hot taps. The contents of the cylinder therefore never come out of the taps, and are effectively part of a closed loop. Is that a fair summary?

The problem is that you are maintaining a large body of water at high temperature for 24 hours a day. The inherent losses are necessarily high, simply because of the differences between the water temperature and the ambient air, and in most circumstances I would therefore need some persuasion that there was any benefit to be gained from the system.

Mike

 

[RogerM]

As Mike Garnham has pointed out, you can remove the need for a new HW cylinder by installing a heat exchanger in place of the immersion coil. However this has the disadvantage that it will only heat water to the depth of the coil - typically 80 cms, and does of course mean that you have no immersion backup for quick hw on a dull day.

This looks like a cunning plan that removes the need to install a new solar hw cylinder, lets you keep your immersion heater, and will heat the whole existing cylinder, feeding the hot water in to the top of the cylinder, exactly where it is needed, and where it will stratify until the cylinder is full. It's called a Willis Solasyphon and it sits alongside the existing h/w cylinder. Here's how it works.

 

[wobblycogs]

That's a really clever idea. I would be interested to see how well it works in practice though. AIUI Andy has a DHW system though so I'm not sure this is suitable. I'd be wary about drilling a hole in a DHW tank as they are designed to resist pressure and I wouldn't want to weaken it. I wonder though if attaching this gizmo to the cold feed pipe rather than direct to the tank would work? I don't think it would be as efficient.

 

[RogerM]

I wonder though if attaching this gizmo to the cold feed pipe rather than direct to the tank would work? I don't think it would be as efficient.

Funnily enough I had exactly the same thought. Maybe just take a T off the infeed from the cold water tank?

 

[RogerS]

..... I'd be wary about drilling a hole in a DHW tank as they are designed to resist pressure and I wouldn't want to weaken it...

No need to worry. It's fairly standard practice ....look up Essex flange.

 

[big soft moose]

.look up Essex flange.

but make sure safe search is on, and swimbo isnt in the room first

 

[OPJ]

Apologies for interrupting this thread but, I came across this link the other day which may be of interest to some. It's designed to store a small amount of pre-heated water entering a combi boiler or storage cylinder and reduces gas. It looks like one of the cheaper options available today although, saying that, it probably doesn't provide as much energy as some of the others

 

[RogerM]

Apologies for interrupting this thread but, I came across this link the other day which may be of interest to some. It's designed to store a small amount of pre-heated water entering a combi boiler or storage cylinder and reduces gas. It looks like one of the cheaper options available today although, saying that, it probably doesn't provide as much energy as some of the others

At around £1500 inc VAT that looks a bit pricey for what it is. I appreciate that is the price fully fitted, but for someone with good DIY skills they could have a full solar system for under £1,000 using a 20 tube panel, or around £1300 if fitting a new twin coil domestic hw cylinder using one of these kits. I have no connection with this company, but I've read many good things about them.

Whilst on the subject of recommendations, I mentioned a neighbour had fitted an installation from NaturalWatt based in Exeter. Whilst his initial experience was very good, the relationship has soured and he has told me that he cannot recommend them.