Can't you just put a pump on the shower, I have the smallest one from Scewfix and it works well.

As for pool or DHW, a kWh is a kWh, but temperature becomes important.
For a shower you need between 25 and 40°C.
A pool about 20 to 22°C, unless you are a serious swimmer and then it will be cooler.

So monitor the solar as it is now and see what temperature distribution you get, this tells you everything you need to know.
Temperature statistics are your friend here, kWhs are not

1) So my first question is, if i put in a megaflow would I have to buy a dual coil on and get rid of any pre-warm?

2) Is there some other way that the solar could pre-warm the water going into the megaflow such as a Thermal store (is this a good idea?)

3) I have 5 bar do I need to worry about stratification (I have seen it mentioned) what should I do?

4) And this is where is gets interesting - I am installing an indoor pool in about 6 months - is the solar better for the domestic hot water or the pool? Both will have gas boilers but I just want to know where you think the energy is best used?

5) If i do use it for the pool which i think would be best as it does not involve storing (which by definition means wastage) How would I do it?

1) You will need a dual coil Megaflo, but you can still have pre-heat & perhaps one of the existing tanks can be reconfigured to do this.

2) The pre-heater tank needs to be a thermal store to avoid risk of legonella. So the cold water feed to the Megaflo needs to go through the coil in the pre-heater tank.

This is a good idea because when the solar panels are hot the solar controller can direct to the flow to the coil in the Megaflo. When only low temperature water is available it can divert the flow to the pre-heater tank.

3) The static pressure does not change the affect of gravity/bouyancy in the tank. However, stratification (or lack thereof) shouldn't be a problem in a tank dedicated to domestic hot water.

4) The DHW requires relatively small quantities of relatively warm water, so needs a relatively small area of relatively high performance panels. The pool requires huge quantities of relatively cool water, so needs huge areas of relatively cheap low temperature panels. It is possible to combine these into one system, especially if you are willing to give priority to DHW production. However, I would keep them separate unless you want to put some work into installing, programming & optimising a relatively complicated control system.

5) The simplest approach which is supported by the more up-market solar controllers is to oversize the panels for DHW & for the solar controller to direct the heat in the following priority:
1. Megaflo
2. Pre-heater tank
3. Pool.

That way heat is never wasted & your panels should never stagnate despite being over-sized for DHW.

David

Posted By: narcosiAm I right in thinking that your suggestion in 2) David is to reverse one of the existing tanks and run the mains water feed to the megaflow through the coil in one of the tanks and run the solar through the outside of it?

Yes. Or if it has two coils, you can run the mains water feed through one & the solar through the other.

Posted By: narcosiWill the coil take mains pressure? and will the outside work at a pressure which the solar can operate at?

That depends upon the coil & your mains pressure, but the coil will be designed to work in a sealed system & should be able to operate safely at 2 bar. If there are two coils the pre-heater tank itself can be vented. If you connect the solar directly to the tank then you'll need a lot of glycol solution. Check the cost of this before deciding on the configuration.

Posted By: narcosiIf I did this on its own without a second coil in the megaflow, am I too assume I would be wasting much of the solar heat?

No, but on a hot day you want the system to prioritise sending hot water directly to the Megaflo, to avoid the boiler kicking in. Sending it only to the pre-heater tank increases the likelihood that the panels will be hotter than the storage tank because the pre-heater tank will be at a lower temperature than the Megaflo. However, it doesn't maximise the amount of useful hot water. In other words, you can end up with lots of luke warm water in the pre-heater tank which means the gas boiler still runs in the summer.

Posted By: narcosiAs for the pool my A-Level physics would tell me that heat exchanging with a large volume of water at between 20 and 30 deg (the pool) would get the most out of the panels as there will be little if any wastage and there will never be enough from the 2 panels I have to heat the pool entirely.

Yes, this is true. You have maximised the amount of energy collected by the solar panels by minimising the temperature of the store, but that isn't the same thing as maximising the amount of useful hot water & minimising the gas boiler consumption. This depends also on the temperature you keep the pool at, the temperature you keep the DHW at, the times when you draw most DHW, the strategy for controlling the solar thermal system & probably a whole load of other things.

David

Posted By: davidfreeborough

Posted By: narcosiAm I right in thinking that your suggestion in 2) David is to reverse one of the existing tanks and run the mains water feed to the megaflow through the coil in one of the tanks and run the solar through the outside of it?

Yes. Or if it has two coils, you can run the mains water feed through one & the solar through the other.

If you did this what would be in the tank its self? I have one tall tank with one coil which is the pre-warmer now and one which has two coils which is the main tank now.

Posted By: narcosiWill the coil take mains pressure? and will the outside work at a pressure which the solar can operate at?

That depends upon the coil & your mains pressure, but the coil will be designed to work in a sealed system & should be able to operate safely at 2 bar. If there are two coils the pre-heater tank itself can be vented. If you connect the solar directly to the tank then you'll need a lot of glycol solution. Check the cost of this before deciding on the configuration.

If you use the two coils as suggested, what goes in the tank its self? What is glycol for?

Posted By: narcosiIf I did this on its own without a second coil in the megaflow, am I too assume I would be wasting much of the solar heat?

No, but on a hot day you want the system to prioritise sending hot water directly to the Megaflo, to avoid the boiler kicking in. Sending it only to the pre-heater tank increases the likelihood that the panels will be hotter than the storage tank because the pre-heater tank will be at a lower temperature than the Megaflo. However, it doesn't maximise the amount of useful hot water. In other words, you can end up with lots of luke warm water in the pre-heater tank which means the gas boiler still runs in the summer.

Why would the preheat tank be at a lower temperature? surely the panels would just keep heating it and the gas would top up the megaflow if needed.

Posted By: narcosiAs for the pool my A-Level physics would tell me that heat exchanging with a large volume of water at between 20 and 30 deg (the pool) would get the most out of the panels as there will be little if any wastage and there will never be enough from the 2 panels I have to heat the pool entirely.

Yes, this is true. You have maximised the amount of energy collected by the solar panels by minimising the temperature of the store, but that isn't the same thing as maximising the amount of useful hot water & minimising the gas boiler consumption. This depends also on the temperature you keep the pool at, the temperature you keep the DHW at, the times when you draw most DHW, the strategy for controlling the solar thermal system & probably a whole load of other things.

David

So in short how the hell do I answer this? should I be finding an installer and taking advice? my experience with pools is that it will want energy all the time even in the summer, so if i remove the solar from the DHW totally i would still be using all the solar energy, but - who knows.

Thanks for your advice, any recommendations on people I could engage on this?

Jon

Posted By: narcosiIf you did this what would be in the tank its self? I have one tall tank with one coil which is the pre-warmer now and one which has two coils which is the main tank now.

If you used the existing twin coil main tank as the pre-heater then you just need to fill it using the existing header tank in the loft.

Posted By: narcosiIf you use the two coils as suggested, what goes in the tank its self? What is glycol for?.

Glycol is an anti-freeze used to stop the water in the solar panels freezing.

Posted By: narcosiWhy would the preheat tank be at a lower temperature? surely the panels would just keep heating it and the gas would top up the megaflow if needed.

Without a solar coil in the Megaflo, the only mechanism for moving heat from the pre-heater tank to the Megaflo would be the mains water flow. The relatively short coil in the existing tank will only add 15-20 degrees to the temperature of the mains water flow. So you'll always need the gas boiler to top it up & compensate for heat lost to the house. Allowing the solar panels to heat the Megaflo gets around this limitation.

Its not just about extracting the maximum amount of energy from the solar panels. Its also about getting that energy in the most useful form.

David

Hello All!

So I think I have a plan - please comment.

I intend to purchase a dual coil megaflow.

I will use the old main tank as a pre-warmer with the solar running through one coil and the mains running through the other. I will plumb the vented body of the tank to the header tank as a heat transfer medium.

The main which will be capped at 3.5 bar the working pressure of the old tank coil will then feed into the megaflow with its gas and solar coils.

As and when we build the pool we may remove the pre-warmer tank do something for the pool.

1) Do we all think this will work?
2) Do we think the mains water will pick up much temp as it goes through the pre-warmer?
3) Do I need to call in a solar guy to look at any reprogramming and biasing the system to the megaflow?
4) should i look at when the gas comes on? surely if the gas heats the tank in the morning as it would in a normal house then the solar will have nothing to do during the day.

You have all been so very helpful

Thanks in advance for your thoughts.

Jon

Posted By: davidfreeborough4) This comes back to my point about when you use your DHW. Ideally you want to keep the gas boiler as back-up. This means it shouldn't be set to fully-charge the tank first thing in the morning or come on at all during the day. Best to keep baths/showers to either early morning or late evening & just run the gas boiler for an hour beforehand, leaving the solar to re-charge the tank.

David

Thanks, I will get moving on it and per your point above - thanks for confirming what i thought which is running the boiler at the end of the day to top it up to temperature before the evenings entertainment sounds good.

thanks again for all your help.

Posted By: narcosimy plan does not involved a vented solar system now, the solar will run through the coil and I assume stay at the 2Bar it is at now. Will I still need glycol?

Yes, but not as much as if you'd used it to fill the tank. The only way to avoid the need for glycol is to use a drain back system which empties the solar panels overnight.

David

Thanks guys!