Solar Cooling - Science topic

This scientific contribution will be of great use to you.

DOI: 10.1080/23744731.2018.1431479

The current article presents the comprehensive thermodynamic modeling to compare the performance and optimization of single-stage LiCl-H2O and LiBr-H2O type absorption cooling system integrated with different solar collector types for the Gujarat, India. A 10 kW system at 7°C is analyzed which includes four different solar collectors (flat-plate collectors, parabolic-trough collectors, flat plate with compound parabolic collector reflectors, and evacuated-tube collectors) attached with insulated thermal storage tank to power the LiCl-H2O and LiBr-H2O vapor absorption system. The study investigated the effect of heat source temperature on performance aspects of systems. Optimum heat source temperature corresponding to energetic and exergetic aspects for LiCl-H2O pair is found to be lower in comparison to LiBr-H2O pair for all collectors type system. The examined performance parameters are exergetic efficiency, coefficient of performance, and area of collector. Exergetic optimization of each system estimated the required optimum collecting area for cooling. At optimum collector areas, capital cost is evaluated. Differentiation between optimized systems determined that evacuated-tube collectors-based technology is most economic and from exergetic point-of-view, parabolic-trough collectors is recommended. For effective comparison and conclusion, key performance indicator is evaluated to select optimum collector and working fluid pair from both thermodynamic and economic criteria. © 2018, Copyright © 2018 ASHRAE.

The simple muiltiplication of the mass by the thermal capacity as Bachir Achour proposes, is valid only at thermal equilibrium. Since buildings are always in a thermally dynamic state, this method strongly overestimente the active thermla capacity. When the ambient temperature continuously changes, the calculation is more complex, and needs solving the equation of heat. Simple mathematical solutions to determine the thermal mass of a multilayer plane building component under dynamic conditions are indeed described in EN-ISO 13786 as mentioned by Edwin Rodriguez-Ubinas.

An experimental method to determine the dynamic thermal capacity of a room was proposed by Van der Maas (see attched paper). The apparent room effusivity can be measured by recording the increase of the indoor temperature after switching on a constant power heat source.

This publication contains very pertinent information for your research. I think it will be very useful to you.

Abstract

In the recent years, numerous studies have been done on Stirling cycle and Stirling engine which have been resulted in different output power and engine thermal efficiency analyses. Finite speed thermodynamic analysis is one of the most prominent ways which considers external irreversibilities. In the present study, output power and engine thermal efficiency are optimized and total pressure losses are minimized using NSGA algorithm and finite speed thermodynamic analysis. The results are successfully verified against experimental data.

you can contact Mr Essaid El Kennassi to help in this question

When the compressor stops and only the fans run, the power consumption can be one tenth of the total consumption of the air conditioning system. This is because the mechanical compression process requires much more energy than fans use to move air through the exchangers. Basic knowledge of thermodynamic theories explains this difference between the consumption of the cooling system while only the fans operate.

I agree and I like the proposition of Bo Miao

Simply because Earth is the only planet inhabited by human beings.

@Jafar M. Daoud. can you please send it to me ? This my email:bokhalfa.mohamed@gmail.com

This is a heat transfer rate maximization problem in the evaporator , in which you have to find an evaporator with the maximum LMTD which means the highest efficiency. Theoritically you can cool down the water as fast as you want but you have design restriction such as refrigrerant inlet temp to the evaporator. In the best scenario the refrigerant inlet temp to evaporator cannot be higher than 2c for your design case and it leads to local water solidification which acts as an insulator. To solve this problem you can recirculate water in tank or add antifrost to tank if you are not using it for sanitary purposes. Higher evaporator efficiency inflicts alot more costs.

Dear Duaa,

Welcome,

Adding to Tony, you can connect fins to the back of the solar panel by using thermal conducting adhesive materials. There are many vendors for such materials one of them Henkel, is given in the attached link:https://www.woronko-glue.com/sg_obrazki_/00002478_normg_001.pdf

Best wishes

Dear Karam Mohammed

your comment is useful, thanks.

Hi

Even if there are lot of Computational tools for designing renewable systems, designing them with mathematical model would be much better.

If you have knowledge in MATLAB, you could easily develop an optimisation tool using MATLAB based on some optimisation techniques. By doing so you would gain lot of knowledge on how the entire system and process works. Below is a publication link attached which gives an overall review about optimisation techniques that can be used for different renewable systems. 

There are many research work undergoing in the field of hybrid renewable systems, most of which uses their own optimisation tool being developed. 

I have also attached the link of another publication which would give an idea about how to develop an optimisation tool using matlab. 

I think the information would be applicable.  

Let's assume you know that you know the power delivered by your solar collector P.

Then, knowing the time of the charging process (which depends on what is your demand on the load side, probably for solar storage is 6-8 h) which is h, the maximum amount of energy you can store is:

E=P*h

knowing the energy density of the PCM:

m_PCM=E/E_PCM

if the density of the PCM is ro_PCM

V_min=m_PCM/ro_PCM

and, to take into account the thermal expansion I would use an oversizing factor of 20%:

V_shell and tube= V_min*1.2

then you have to ask the producer of the exchanger for an exchanger with this volume.

Following may also helpful to you.

T.S. Ge, Y. Li, R.Z. Wang, Y.J. Dai, A review of the mathematical models for

predicting rotary desiccant wheel, Renewable and Sustainable Energy

Reviews 12 (2008) 1485-1528.

Dear Joshi,

Besides the factors affecting the performance, I totally agree with Yousif' answer. This phenomenon is what so called the 'thermal inertia' of the collector. You will find a time lag between the solar radiation profile and the that of efficiency. 

Regards

Mass transfer as a result of difference in the molar concentration of the transferred substance through each medium in both sides.

The governing law is Fix law  of diffusion in rest mediums.(similar to conduction law in HT)

When dealing with moving medium , the governing equation takes into account the Stefani's flow phenomenon associated with bulk fluid motion.(similar to convection law in HT)

Similarity between heat and mass transfer coefficient in case of moving medium.

The driving force here is molar concentration difference.

You also need to know the film theory when dealing with interface between two fluids.

Sensible heat, heat of vaporization  and heat of dilution are sources of heat transfer process .

You can find that indetails in "mass transfer operation by Trebal"

In addition to that youneed to estimate the effective interracial area at the interface and correlated mass transfer coefficient based on bed type

For comparison of alternative solutions, you select a number of comparison points for the completed system (ideally using some life cycle analysis method to get all effects over time).

Each point of comparison should be a characteristic or parameter than can be selected or measured/calculated.

For each solution you have to evaluate each characteristic and make a measure of how important it is. Each comparison point needs to be reduced to a common scale, if the dimensionless variable way is required:

Examples to illustrate some ways to assign points:

Mass: <1000 kg = 2 points, 1000 kg - 2000 kg = 1 point, >2000 kg = 0 points. (Less than 2000 kg is good but not absolutely required)

Price: <$1000 = 10 points, $1000-$1500 = 5 points, > $2000 = -200 points. (Less than 1500 is a bonus, more than $2000 is not allowed)

Time to recover after interrupt: 10 points - (number of seconds) / 2. (lets say more than 20 seconds is a bad thing and should give negative points)

Adding all the points for each alternative solution will give a dimensionless quantity to compare, but the valuation of how each parameter, how each point scale is designed, is up to you.

This is a lot of work if done complete, so a study to select which characteristics are most important is probably a good way to start.

 Thank you for your reply Mr. A.M. Alatyar

But Maddali Silica gel is not a liquid. I am looking for a liquid so as to pump it round the system .

I have also used EES for this purpose, Frankly speaking, for LiBr-H2O system transient analysis is quite difficult. First go for steady state modelling. There is a lake of resources available for transient state analysis. So go for steady state analysis. 

you are more than welcomed

Thanks for your reply.

Is 40,000 $ cost for liquid desiccant cooling system?

Thanks for your answer, 

Dear Marcelo,

EES is one of the most recommended software for simulating energy systems. It has a good library which contains the thermo-physical properties of several working fluids (refrigerants). Instead, you can use Matlab/Simulink which is very common however you will need an assistant software for the thermo-physical properties of the refrigerants such as REFPROP...etc. Also, TRNSYS is a good option for simulating solar and HVAC systems.

I am attaching PDF files of EES & TRNSYS of more detailed information

I hope this could help you

You can prevent boiling using a mixture of water and propylene glycol. In the following link you can find the variation of the boiling point of the mixture as a function of the percentage of glycol:

I hope this information can help you.

Vapour compression cycle can be used to produce refrigerating effect. The power produced from solar panel should be sufficient enough to run the compressor of refrigeration system then you can produced the ice but it requires large space and investment.

To add to what Shashank Vyas has explained, it is important to understand the cooling requirement in terms of BTU/hour.   To do that, you need to create a simple thermodynamic model of the cooling space, the walls of the space and the outside.  Some questions to help figure this out 

1.  how big does the space need to be?

2.  what is the maximum external temperature and the desired average internal temperature you need to achieve.

2a.  You also need to know what the thermal resistance of the walls are so you can figure out the rate heat will leak from the cavity.

3.  how much can the internal temperature fluctuate beyond the average in #3?

4.  What material will be placed in the cooler?  Of all materials, water has the highest specific heat (ability to store heat energy)  so assume ambient temperature water as the  worse-case in terms of placing something warm inside that has to be cooled.   Then calculate how much heat that water would have to lose to lower its temperature to the desired average #2.

5.  With all of this, you should be able to calculate the rate of  heat removal the fan and evaporative cooler have to  perform.   

6.  This BTU rate is a unit of work.   If you make a reasonable guess about how efficiently the evaporation+fan work  (BTU rate/Watts of input energy to fan) you can then decide how big the fan must be and therefore how big the electrical source have to be.  If there is a flow pump to circulate water, then that too will factor into the electrical overhead.   Often times the pump is very small since all that is required if to keep the fabric moist.  more water flow than that is wasting energy.

Just about any basic thermodynamics textbook has all the formulas and examples for this kind of calculation.  Hope this helps.

This book chapter will answer your question...."3.14 - Solar Cooling and Refrigeration Systems"

Reference Module in Earth Systems and Environmental Sciences, from Comprehensive Renewable Energy, Volume 3, 2012, Pages 481-494

G.G. Maidment, A. Paurine