megaflow, solar and combi boiler...possible??

[BruceB]

Thanks for digging that out Gavin. I understand the point. Not bumped into it to date as all I have been installing with solar are thermal stores.

 

[Gavin A]

re willis.

It's just a more expensive, but more prefessional looking version of an external heat exchanger. We've got an external heat exchanger fitted to our second tank, and fitted a couple for SWH customers who didn't want to replace the tank.

They work well, dropping the hot water directly into the top of the tank via thermosyphoning, so reduce the issue of ending up with tanks full of luke warm water instead of half a tank of hot water, but you do need a method of regulating the speed of the water flow through the heat exchanger with temperature if you're going to get useful hot water at over 50 deg the entire time - we've used a specific Thermostatic valve for this purpose that seems to work well, though it's not actually designed for this purpose. This also prevents cold water flowing through it when you're drawing off hot water at the tap.

I think the willis unit might just use the long thin pipes to regulate the flow, but I'm not entirely sure.

One issue though is that the thermosyphoning only really works from the top of the heat exchenger upwards, so once the hot water gets level with this (from the top down), the flow slows a lot, so effectively the bottom 20 cm or so of the tank aren't really used most of the time. It's not so much of a problem though IMO as it operates as a fast recharge / semi combi type system so will rapidly heat the top of the tank to temperature to be usable again instead of having to wait 2-3 hours for usable temperatures with a dual coil set up if you've emptied the tank of hot entirely.

 

[solarsavings]

Bruce I'll have a look later today if i can and find you a link or you could try either the ihpe, wras or cibsie website yourself. It was around 2008-9 that we were stopped from feeding water above 23c to combi's prior to that it was a fairly simple job.

You don't need to use either a heatbank or thermal store (provided you have at least 1bar mains pressure) if you're intending to heat the cylinder via an immersion heater as both are far more expensive than a direct unvented cylinder combined with the intasol valve. I have my own heatbank cylinders made in the rm factory and add the other components myself when combing other heat sources.

 

[sambotc]

I would keep it simple. Standard indirect vented/unvented cylinder, coil taken off combi heating via an s plan arrangement. You could run the hot water from the combi to a kitchen tap/utility or similar so that these outlets have instant hot water and this will help reduce de-stratification in the cylinder through the day. Standard immersion can be run off the P.V with combi to boost when P.V doesn't suffice.

You get the best of both worlds, instant hot water in the kitchen at any time from combi and a tank full of hot water for baths/showers in the evening once the P.V has had enough time to heat the capacity of water. The only non standard piece of equipment would be the immersion switch (immersun or similar)

The biggest question is, would the initial outlay be worth the saving of gas consumed by the combi?

 

[solarsavings]

See this link Bruce New Page 2 It was 2009 around the time Ferroli lost wras approval for their system which was very similar to the alpha solarsmart which still has approval.

Having thought about it. Someone with a combi boiler wanting to heat water from their pv system should imo use my suggestion first, next would be sambotc's and only use worcester's if there was a possibility of adding another heat source at the same time or in the future. I could of course be seen to be biased but it is the best solution regardless of that.

 

[sambotc]

Hi Solarsavings,

what the reason for specifying Worcester (boiler?)out of interest?

 

[solarsavings]

I wasn't ;-) Worcester suggested using a thermal store or heatbank as being the best in this instance, it isn't.

 

[sambotc]

Haha no worries, I mis read your post.

If the potterton performa 24 eco he can take preheated water I agree. Not sure if it can though hence my suggested method.

Have you used the intaeco valve much solarsavings? If so how do you find them and who supplies them to you? (if you could PM a rough idea on price that would be great)

 

[sambotc]

Having had a quick look at the performa HE it appears to be a band B so no full modulation. I would hazard a guess that it isn't suitable for pre heated water as it would work off a set temperature rise

 

[solarsavings]

I have used them quite a bit (mostly before pv) trade price is a little less than £170 but you can buy Grants combisol valve ? for around £125 and they will do the same job. You could of course make your own using two tmv's as we used to do.







EDIT: for clarity. my use of 1bar is working pressure or if you prefer, open pipe.

 

[sambotc]

How do these blending valves overcome the issues with the pre heat cylinder pasteurisation? If the water is only heated to 25 degrees in the tank through the winter months and then boosted to 60 through the combi in seconds, surely that doesn't meet the required amount of time to safely eliminate legionella?