3 replies to this topic

[KR]

Dear all,

I am working on Micro Brewery Project and realized that most of energy is used in water heating. Therefore, we are planning to design Solar Water Heater and want to arrive break-even point.

Our aim is to heat up water from 10 to 75 oC. I have calculated heat load required, surface area required for the absorber/collector and savings. Please find the attached spreadsheet for the calculation.

My questions are:

1) Is there any precise method for finding out collector area for solar heater than what I have suggested?
2) How is it possible to conclude that this heater will achieve target temperature i.e. 75 oC?

Thanks in advance.

Attached Files

•  Solar_water_heater__calculation.xls   29.5KB   78 downloads

[astro]

Isn't it great to see a question presented to the forum where the originator has done some engineering to get things started? My thanks.


I may have missed something but I can't see in the analysis by Sorter, et al, where there has been account of heat loss from the system in question. The implied assumption that I draw from their paper is that they've assumed heat losses to be zero. I would expect the heat loss to increase with a reduction in ambient temperature and given that your ambient appears to sit at about 10°C, then this is an issue to be wary of.

Sorter hasn't really explained the methodology used for deriving the collector area equation, which immediately piques my concern. They have also opted for an "active" system, i.e. pumped, and their analysis doesn't appear to account for this energy input and operating cost.

Unless you've chosen the same mechanical design, then you're potentially making an incorrect application of Sorter's design equation. I'm just offering a check question to you here.

I did a quick search and found the following paper by Bolaji:
Bolaji Paper

Notable differences between Bolaji and Sorter:
1. Bolaji investigates a natural circulation / thermo-syphon design, i.e. "passive" system
2. Bolaji presents a transparent description of the mass and energy balance equations applied to the problem analysis
3. Sorter considers an indirect heater / Bolaji investigates direct heating

Figure 6 in Bolaji's paper shows the relationship of solar insolation upon collector efficiency. The insolation used in your spreadsheet equates to about 130W/m2, which doesn't show on figure 6 but would result in a number significantly less than 40%.
Based on this I would caution you to confirm that use of a constant 50% efficiency for you application is a valid basis.
Presumably active systems have a flatter insolation/efficiency curve but you would need to find out the detail there. Personally, I doubt whether the curve is perfectly flat.

[riven]

I will ask my collegues for an example effiency for this application but try searching references at www.ecn.nl for solar collector efficiencies.

From my limited knowledge typical efficiencies for orbital solar power collectors is 40%, here on earth you are looking at 20% or less.

Hi KR,
I know this thread is a bit old now - sorry... Its been a while since I've looged in.
I hope a reply is still relevant!

I'm a process engineer and brewer. I've done a little bit of simulation of solar hot water systems in the past and have noted that its a bit tricky to estimate the likely gain from a solar system at any given time or over any given month etc. These simulations have involved factors for specific collector models and sun-angles etc. It is very dependent on your location, how cloudy it is when it is cloudy etc...... and the 'overall efficiency methods' are obviously even more crude.

Where I live - in Victoria, Austalia (not the it is reasonably common to reduce gas/electricity use for hot water by say 60% or more depending obviously on useag in relation to collector size. I have seen figures for vacuum tube systems of 70% collector efficiency. (these systems are usually less effected by angle of incidence and temperature-difference than flat-plate collectors) I suspect the 50% figure you use is ok/conservative - justifiable at least!. Perhaps the best thing to do is talk to local suppliers and ,better still, users and ask what performance they are getting given their particular collector type size and demand. This will help work out what number and size of panels you want/can afford and enable you to get a better figure for payback calcs.

Have you thougtt about the type of system you would use? Vacuum tubes can achieve very high tempreatures even at quite high latitudes. A very well insulated heating fluid tank (water and anti-boil additive) with a heating coil in it is a good way to use high temperature capabilities. Pass the water for your brewing through the heating coil rather than directly through the collectors.

I've been trying to come up with some ways of using heat recovery in small scale brewery. Not always convenient in any batch system. Initial cooling (first half?)of hot wort could be used to make hot water which could be put in an insulated tank and then used as part of feed for next batch directly or at least warm up incoming fresh water for next batch via heat exchanger. I've seen similar things done in the dairy industry.

Good luck.


Nat.