The Great 'Get Paid To Generate Energy' Hunt

John_Pierpoint

"Time, Temperature & Turbulence" as we would say when I was in the central heating boiler business in the 1960's

jessielet

You are extremely lucky to have been able to install your own system. In my case, we got a certain company to install solamax panels 3 years ago--they were inefficient from the start and we knew too little to question them. Anyway, it has now stopped working. When we turned on the switch, there was a smell of burning and all the electrics were blown. We've tried several agencies etc to help with finding a suitable specialist but they kept telling us to go back to the original installers ( it's like a !!!!!!). When we did, they sent us a massive quotation. Please could you give us some advice on what to do. Thanks

Cardew

jessielet wrote: »

You are extremely lucky to have been able to install your own system. In my case, we got a certain company to install solamax panels 3 years ago--they were inefficient from the start and we knew too little to question them. Anyway, it has now stopped working. When we turned on the switch, there was a smell of burning and all the electrics were blown. We've tried several agencies etc to help with finding a suitable specialist but they kept telling us to go back to the original installers ( it's like a !!!!!!). When we did, they sent us a massive quotation. Please could you give us some advice on what to do. Thanks

Is this a solamax solar thermal hot water system or a solamax PV system(both type of panels are caled 'solamax')

Why not name the company?

How much did you pay for the installation? and how much is the repair quotation?

Most solar firms only give a 2 year guarantee on the system.

green_as_grass

Zeupater
Thanks for that detailed reply, and the link.
I'm still wondering whether heat transfer is the same in all directions given that convection tends to transfer heat upwards.
I'd also be interested to know how long it would take to reach thermal equilibrium in practice. Difficult to calculate given the three forms of heat transfer and all the variables. Does anyone have 'real life' experience from their own thermal store? That is, how long is there a significant difference in temperature between top and bottom of the store during a period of no significant heat input or output?

When heat is taken from the store (ie. when a hot water tap is opened) you mention the resultant convection as the DHW coil cools the water surrounding it. Could this not be regarded as a 'good thing' in that the cooled water falls to the bottom of the tank and is replaced by warmer water around the DHW coil, ready to warm the next amount of hot water required? In which case the effect of having baffles in the store might be counter-productive.

zeupater

green_as_grass wrote: »

Zeupater
Thanks for that detailed reply, and the link.
I'm still wondering whether heat transfer is the same in all directions given that convection tends to transfer heat upwards.
I'd also be interested to know how long it would take to reach thermal equilibrium in practice. Difficult to calculate given the three forms of heat transfer and all the variables. Does anyone have 'real life' experience from their own thermal store? That is, how long is there a significant difference in temperature between top and bottom of the store during a period of no significant heat input or output?

When heat is taken from the store (ie. when a hot water tap is opened) you mention the resultant convection as the DHW coil cools the water surrounding it. Could this not be regarded as a 'good thing' in that the cooled water falls to the bottom of the tank and is replaced by warmer water around the DHW coil, ready to warm the next amount of hot water required? In which case the effect of having baffles in the store might be counter-productive.

Hi

With conduction the heat transfer will be equal in all directions, given the same conditions in all directions. If there is a steeper thermal gradient in one direction and the materials are constant (e.g copper) then more energy will migrate towards that direction in a given time period. As heat is the form of energy being discussed and energy flow is from high to low, the conduction as described by a top heated thermal store will be downwards.

What now needs to be considered is that there is a difference between the effect of conduction in a solid (copper etc) and either a liquid or gas. Imbalanced conductive or radiative heat changes within either a gas or liquid will cause convection to occur and, as John_Pierpoint correctly stated a couple of post ago, the transfer of heat is dependent on "Time, Temperature & Turbulence". In the tank the turbulence is being caused by the convection, the result of which is to increase both the temperature gradient and boundary areas between volumes of water having different temperatures. It is important to recognise that it is not the convection itself which accelerates attainment of equilibruim, but the conduction of energy across steeper thermal gradients which have been caused by the convection. From this you will see that in a convective system, the greater the turbulence, the greater the temperature gradient, the shorter the time to reach thermal equilibrium.

I hope that this helps to explain why it is important to prevent large convective cells forming within a thermal store through the use of the baffles.

Now regarding the cooling effect of drawing off hot water. This will really depend on the efficiency and configuration of your heat exchanger. I suppose that if the exchanger coil is contained entirely in the top of the tank there would be a different convective effect than having a bottom entry 'through tank' exchanger where the cold supply would take the lower grade energy available at the bottom of the tank & progressively take more of the higher grade energy available as the flow rises through the tank without simply depleting the highest grade energy at the top, thus reinforcing the original point that the introduction of lower grade energy to the bottom of the tank when available is extremely important as it both reduces the whole system thermal gradient and preheats the mains supply.

Like yourself, I would be interested to see the test results for both long term stratified storage along with results for a standardised usage pattern relating to a range of standard heat input models as this is really the only way to compare equipment. This should be readily available from all manufacturers for all recommended configurations.

Regards
Z

zeupater

Hi All

Regarding thermal stores, there's a great discussion from last year on the gbf here (http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3494&page=1) if anyone has a couple of hours to kill ..... :cool:

It doesn't concentrate on any one form of energy input, or even one type of store, but some of the posts include useful information on 'real world' HS performance.

Regards
Z

Cardew

Whilst not absolving myself from some of the blame, a thread on the merits/demerits of FIT payments for generating electricity has 'degenerated' over the last few pages into a highly technical- albeit interesting - discussion on DIY plumbing.

albyota

Cardew wrote: »

Whilst not absolving myself from some of the blame, a thread on the merits/demerits of FIT payments for generating electricity has 'degenerated' over the last few pages into a highly technical- albeit interesting - discussion on DIY plumbing.

cardew I agree, maybe there should be seperate threads for energy, power, heating, and of all forms of fuel/energy i.e. Gas, Electricity, Oil, LPG, coal, etc.. solar thermal, solar PV, FIT, RHI etc... however, where would you draw the line, as you know, most of these topics do interlink and morph into one.
nevertheless very interesting.

albyota

O.K to get this thread back on topic, last weekend, Fri, Sat, Sun, the three hottest days of this year I think, my 4 square metres of flat plate solar thermal panels yielded about £2.50p worth of 'free' hot water into a 210 Litre twin coil cylinder, the tank got to 80 degrees and held an average of +65C until Wednesday evening after four of us using it for washes/showers over the six days, albeit quite cool showers due to the warm weather, this stored hot water cannot be used for heating in the summer. At a cost of £2.5K 3 years ago, I should start to get my money back when I am around 104........roll on!!

Cardew

Of course your £2,500 would have yielded about £300 in interest in the 3 years and you will have saved about £150(if you are lucky) in 'free' hot water!