Solar solution - do I need two cylinders?

PocketJacks

Folks,

Just wondering if you can give me a bit of advice on using solar panels with a pressurised hot water system. I am in the process of designing a new house and would like to go with the solar option with an oil boiler booster. The architect is trying to push us in the direction of locating the cylinders in our utility room.

I am aware that best practice states keep the cylinder(s) close to the appliances i.e. the kitchen however the cylinders proposed will impact what we can do with the utility room.
On the plans he now has 2 large cylinders located in the utility room. My feeling on this is that one large (300ltr) dual coil cylinder is required.

My questions:

Are 2 cylinders required here or is he getting his wires crossed and one of these should be a heat exchanger (he is adamant 2 are required)?

Can these cylinders be located out in the car port (fully covered area)? The oil boiler is located here and in close proximity to showers and bathroom.

Cheers,
PocketJacks

CJhaughey

You only need one 300l cylinder with dual coils, one for oil and one for solar.
Your arch. is not very conversant with solar tech, best engage someone that is for the solar part of the build.
The car port may be covered but is likely to be very cold in winter and you will find unacceptable heatloss from your cylinder or high fuel consumption as your boiler tries to compensate for heatloss.

nmacc

I'm guessing that the panels are for water heating only. If the architect is aiming for a contribution towards space heating however, then the second cylinder could be a buffer tank.

Assuming you're just heating the hot water, the first task is to figure out how much you need. A rule-of-thumb is 50 litres per head, per day. So a family of 4 will use around 200 litres of hot water per day. This is a generalisation and it may be a bit higher with a pressurised system, simply because more water will come out of the taps.

With a solar thermal system we aim to store 2 day's supply to cover dull periods, so our family of 4 would need a 400 litre cylinder. A family of 6 would need a 600 litre cylinder and this can be a problem as they're not very common. They are available certainly, but the rarity makes for high prices, as this example shows.

At that price it can be cheaper to fit two smaller cylinders. This can be turned into a virtue as they can be configured (with a little extra plumbing) in such a way that the full output of the panels is directed to one cylinder first, meaning that it heats up rapidly and recovers quickly. When the first cylinder has reached temperature the heat is switched to the second cylinder.

We've installed a couple of these creative solutions and they work well. Where it can get tricky is the anti-legionella set-up. You need to be able to heat up both cylinders to 60C reliably and that can sometimes be tricky, depending on the boiler setup. It can be done with just one immersion, but it needs creative thinking.

AckwelFoley

nmacc wrote: »

A rule-of-thumb is 50 litres per head, per day. So a family of 4 will use around 200 litres of hot water per day. This is a generalisation and it may be a bit higher with a pressurised system, simply because more water will come out of the taps.

With a solar thermal system we aim to store 2 day's supply to cover dull periods, so our family of 4 would need a 400 litre cylinder. A family of 6 would need a 600 litre cylinder and this can be a problem as they're not very common. They are available certainly, but the rarity makes for high prices,.

The info here is pretty accurate imo, but as for the sizing of the cylinder i would have to tend to disagree a little on one part..

With 300L cylinder you have to remember that this cylinder is capible during the summer to get to 65 degrees, and hot water that we use to shower is at max 35 degrees you wil have more than 300l of hot water efictively after its mixed in the tehrmo mixing valve.. ive never seen a system for 6 ppl ever require a 600L cylinder... one of the biggest reasons other than the price.. is the SIZE.. a 600L would be massive in the house.


And OP, im not a big fan of architects advising on energy needs particularly renewables, you need an energy accessor. I have alot of dealings with architects plumbers and engineers, and the vast majority at the moment have only a brief understanding mixed with misinformation at the moment.

I could write a book of the mind shattering rubbish i here comming from the mouths of the so called pros

One plumber laid underfloor at 12" centers and used NO SCREED.. jus plywood...

.. and this is where a bad reputation comes from...

sinnerboy

snyper wrote: »

One plumber laid underfloor at 12" centers and used NO SCREED.. jus plywood...

.. and this is where a bad reputation comes from...

:eek::eek::eek::eek:

you sure he was a plumber ?

AckwelFoley

sinnerboy wrote: »

:eek::eek::eek::eek:

you sure he was a plumber ?

a second generation one!! A good plumber, but just dodnt know the firt thing about underfloor or renewabls

Iv a serious gripe with alot of ppl in the renewable scene, giving misinformed opinions based on rubbish like ive just stated in the previous post. OR giving a inccurate biased opinion about one form of renewable that they just happen to be selling.. Source your supplier and if they only deal in one or 2 forms of renewables you can be sure they wont give you an unbiased viewpoint.

90% of all the stories you hear about geothermal and air to water is because some jackass too a look at the house and said eh.. yea 16 kw unit will do nicely..

Dont take my word for it.. its the truth.. one of the largest builder providers in Ireland asked me for a price on a 16KW unit.. i said no problem.. have you a set of plans and a ber please..

No was the answer to both.. i said sorry.. but how do you know you need a 16kw unit? He said oh the plumber.. hes knows what he wants hes an expert.. hes done it before...

Now.. UNLESS HE HAS SOME AMAZING ABILITY TO DO A VISUAL BER USING HIS PAIR OF AMAZING THERMAL HEAT LOSS DETECTING EYES its impossibl for him to know what size unit he needs.. this then will lead to the unit being too small or too big and either will lead to an inneficently running system.. and giving the industry a bad name.

Plans + BER Assment +correct installation and supervision of insulation = kw/h figure and from that the unit is sized accurately, and return on investment is acheived.

If you are not prepared to do that, dont waste your time with renewables.

mdinee01

Synper - The most sensible advice I have seen on the whole topic of renewables !!!

I have yet to engage the services of a BER, but intend doing so when doing my own build later this year/early next year.

sinnerboy

Snyper - your a decent bloke for sure

nmacc

snyper wrote: »

With 300L cylinder you have to remember that this cylinder is capible during the summer to get to 65 degrees, and hot water that we use to shower is at max 35 degrees you wil have more than 300l of hot water efictively after its mixed in the tehrmo mixing valve.. ive never seen a system for 6 ppl ever require a 600L cylinder...

Snyper, you definitely take your showers cooler than I do; I take mine at 43 degrees and my wife likes hers hotter.

As for cylinder sizes, the larger size is based on one day's reserve: we have a family of 2 adults and 2 small children and a 210 litre feed-&-vent cylinder. I allow it to reach 78 degrees and we find it holds two day's supply. However we recently added two teenage visitors to the mix and that definitely reduced it to one day.

A client of mine has a family of 5 and a 300 litre pressurised cylinder which also heats to 78; they drain that daily.

A 600 litre cylinder would be very big and most of my clients have to settle for one day's supply simply because the hot press or budget won't fit anything larger. A few of my clients have been able to opt for the recommended amount and have been very pleased with the result. An example being a family of 5 whose new heating system (not fitted by us!)failed and had to be stripped out over several days last November. They were extremely complimentary of the solar system that supplied all of their hot water during the repairs.

AckwelFoley

nmacc wrote: »

Snyper, you definitely take your showers cooler than I do; I take mine at 43 degrees and my wife likes hers hotter.

.

Whilt i can agree with you somewhat on the cylinder sizing, you also have to remember about the amount of panels you need to heat a 600L cylinder. and peoples budget comes into account.

Ive honestly foound that 35 - 40 is the more common temp setting for showers. If youre wife wants it hotter so be it but it is an unecessary waste.

But eveyones different i suppose

The Mira Advance ATL is the first thermostatic electric shower, (controlling to +/- 1 degree centigrade) available.
It incorporates push button control for flow & on/off control plus the ATL ‘Flex’ variant has an extended temperature control lever for easier grip. A maximum temperature setting can currently be set to ensure the outlet temperature does not exceed 43 degrees centigrade. See the Flexible Showering section of the website

nmacc

snyper wrote: »

Whilt i can agree with you somewhat on the cylinder sizing, you also have to remember about the amount of panels you need to heat a 600L cylinder. and peoples budget comes into account.

As I said, I rarely get to fit the system described, but it is the way it SHOULD be done, all other things being equal. In practice the difference in panel area is not usually a huge part of the cost and, if fitting vacuum tubes, it only takes slighty longer to fit a 30-tube panel compared to a 20-tube.

It's also possible to fit the panels for one day's consumption, but use the 2-day sized cylinder and I've done this a few times. Obviously it's a compromise and you can end up with a large amount of lukewarm water, but in the kind of weather we've been having lately it works very well.

I know that some of the companies who've been in the business for may years adopt this approach and dispense with a heat dump. It seems a bit chancy to me, but I have completed one system on this basis and it has has been very successful.

No6

snyper wrote: »

Plans + BER Assment +correct installation and supervision of insulation = kw/h figure and from that the unit is sized accurately, and return on investment is acheived.

If you are not prepared to do that, dont waste your time with renewables.

Very good advice snyper there too many cowboys selling renewable rubbish out there, an awful lot of people are getting burned by greedy suppliers / installers or perhaps just plain incompentent ones. There are some good installers and systems its a case of buyer beware and do loads of research, dont believe everything your BER assessor tells you he could be the self same plumber too!!!:eek:

AckwelFoley

No6 wrote: »

Very good advice snyper there too many cowboys selling renewable rubbish out there, an awful lot of people are getting burned by greedy suppliers / installers or perhaps just plain incompentent ones. There are some good installers and systems its a case of buyer beware and do loads of research, dont believe everything your BER assessor tells you he could be the self same plumber too!!!:eek:

Yes and no

We as a supplier had thought about doing BER assements for customers as an extra service but, on further thought it wouldnt be a good idea.

Mainly because it would be somewhat of a conflict of interest to do the assment and supply the products.

We would recomment reputable and established INDEPENDENT accessors.

My recommendation at the moment is NEA - Nationa Energy Accessors, they are a nationwide frachaise. But yes, other than that i agree fully with you.

nmacc

snyper wrote: »

We as a supplier had thought about doing BER assements for customers as an extra service but, on further thought it wouldnt be a good idea.

Mainly because it would be somewhat of a conflict of interest to do the assment and supply the products.

This is a position taken by some of the agencies also, but it need not be a problem. I think that part of the difficulty is the immaturity of the industry. A well-established industry should have a clear set of professional ethics and the signed-up certified members should be educated about those ethics and held to account.

I did the BER course primarily as a way of increasing my own knowledge of insulation and heat loss calculations. I would be quite comfortable carrying out an assessment and then quoting for a job on the property, simply because I would advise the client to follow normal procedures and obtain 3 quotes prior to proceeding.

AlanD

We're just about to install a solar water heating system, well, we're just trying to find the right supplier now.

But seeing as you are talking about tanks, which is better, copper or steel and why?

And then again, some offer to give us a 210 litre tank and other's, a 300 litre tank. All but one said we would need to get our own plumber to fit the tank, which I thought odd. So how much does it generally cost to fit a tank, seeing as that is extra.

Would we regret getting the 210 litre tank?

CJhaughey

Alan
It depends on how many people you have in the house, and what kind of demand there is.
Solar tanks are generally oversized compared with normal tanks, we have 2 kids and a 400l tank and find it good.
We can wash the clothes with solar heated hot water and run a bath at night for the kids and not have to worry about not having enough the next morning for a shower.
Better oversize your tank then undersize it.

MickLimk

AlanD wrote: »

We're just about to install a solar water heating system, well, we're just trying to find the right supplier now.

But seeing as you are talking about tanks, which is better, copper or steel and why?

And then again, some offer to give us a 210 litre tank and other's, a 300 litre tank. All but one said we would need to get our own plumber to fit the tank, which I thought odd. So how much does it generally cost to fit a tank, seeing as that is extra.

Would we regret getting the 210 litre tank?

Replacing the cylinder is probably the worst part of installing any system, they probably just want to avoid it if at all possible! It can take quite a while if the existing heating system needs to be drained down, the cylinder replaced and then the system refilled, bled & checked.

Getting your own plumber to install the cylinder means that your solar installer isn't liable for any leaks that may happen on anything outside of the solar loop. It also means that they don't have any responsibility for your existing heating system not running as it was before a drain down.

Are you buying the solar components yourself or is the installer providing them?

CJhaughey wrote: »

Alan
It depends on how many people you have in the house, and what kind of demand there is.
Solar tanks are generally oversized compared with normal tanks, we have 2 kids and a 400l tank and find it good.
We can wash the clothes with solar heated hot water and run a bath at night for the kids and not have to worry about not having enough the next morning for a shower.
Better oversize your tank then undersize it.

Agree with CJH here with regards to the usage and demands. I'd certainly go for the 300 litre myself. Down the road, if you happen to find that your water is not getting as hot as you'd like, then it's a hell of a lot easier and cheaper to increase the panel size than replace the cylinder again!

Test6699

The first question to ask is what type of solar panels are being used.
Are they flat panel or vacuum type. ie inefficient or efficient.
The second question is on the storage of this energy. Will it be copper, stainless steel. After this question the type of heating in the cylinder. Is it coil heating or a superior heat exchanger type.

Obviously cost goes up but its a long term investment and at the min a vacuum type panel, stainless steel with very high insulation qualities.

I would like to know myself the cost of a high quality vacuum type heat changer panel myself of about 6m2.

CJhaughey

Test6699 wrote: »

The first question to ask is what type of solar panels are being used.
Are they flat panel or vacuum type. ie inefficient or efficient.
.

I am not sure you know what you are talking about.
You are making gross generalisations about two type of solar collectors which is wrong.
There have been tests done by the swiss solar testing institute which show that high quality flat panels are some of the efficient collectors available, and conversely that cheap chinese evac. tubes can produce very very poor results.
It all depends on the quality of the collector not what type it is.