1. June 30, 2014 SOLAR ASSISTED FACILITY COOLING
Utilizing SOL’s Energy
The advantages:
 Solar cooling is particularly useful in the summer months or in tropical regions throughout
the year because of the increasedamountof solarenergythat is available and the apparent
demand for cooling energy.
 The match between the plants performance profile and the consumption profile makes it
possible to have a very efficient energy supply system without the need for a large store.
 Conventional air-conditioning systems have a substantially higher level of electricity
consumption, which represents an enormous load for the power grids. For solar cooling,
only approx. 20 % of the power needed for conventional cooling is required.
 Solar plants are environmentally friendly. Solar cooling reduces the burden on the
environment to a minimum. These plants are operated with environmentally friendly
refrigerants and they do not emit any CO2 emissions. This represents a significant step
towards achieving the climate targets.
 Comparedtoconventional coolingsystems,the life time of the components of a solar plant
is substantially longer (20-25 years).
 Cost savings also play a crucial role. This means that the ongoing energy costs, e.g. for gas,
coal,oil,are substantiallyreducedas the solar cooling is operated using solar energy. Costs
are only incurred for any back-up system that may be required.
 As solar plants contain virtually no moving parts, the maintenance and repair costs are
reduced considerably.
How to proceed:
a) At first there needs to be clear understanding of the load balance of the facility. Generally for
buildings or facilities in sub-tropical or tropical regions, the thermal consumption exceeds the
electrical consumptionintermsof climate control versus lightingandpower.Anin-depth survey
has to be conducted. From the data collected, a target needs to be developed what states the
desiredlevel of grid energy replacement for solar energy. This number will be a percentage of
total building load or kWh/yr.
b) A secondconsiderationisthe space insquare metersavailableforasolar thermal applicationfor
capturing of the available insolation. Solar irradiation or global solar potential is expressed in
kWh/m2/dayor peryear.Not all of thisenergycan be capturedsince the ‘collector’ is subject to
various categories of energy losses both internal and external. (F.i. Reflection, radiation, heat
transfer coefficients etc.)
c) A thirdconsideration,whichhas correlation with a) and b), is the method of energy conversion
that will be utilized in order to convert solar heat into building cooling/heating. (Climate-
control). The choices here are ‘low temperature’ and ‘medium temperature’ conversion. Both
methodshave theirspecificproperties, furtherexplainedbelow.(There is a third method that is
not consideredhere and this concerns ‘high temperature’ conversion where the collectors are
more of an industrial type and support industrial processes.)

2. June 30, 2014 SOLAR ASSISTED FACILITY COOLING
 Low temperature collection is usually done with ‘flat plate’ collectors. These are
developedfordomesticpurposes(hotwatergeneration) butare alsosuitable for energy
conversion by means of desiccant adsorption chilling and single effect absorption
chilling.Desiccantintake airtreatment(de-humidification)isanadditional way to utilize
low temperature solar heat. The temperatures associated with this method are in the
range of 60 – 90 ⁰C. Efficiencies(dailyaverage) will be in the order of ±40%. This means
that of an average insolation of 5 kWh/m2/day, 2 kWh/m2/day can be captured and
utilized.
 Mediumtemperature collection is either done with ‘advanced flat plate’ or ‘evacuated
tube’ collectors. These are particularly meant for dual effect chilling and medium
temperature processes since the water outlet temperature of these collectors can be
over 100 ⁰C. (Up to 150 ⁰C is possible when the system is suitably pressurized, P=4.8
Bara). Efficiencies of evacuated tube collectors can be in the order of >50% (daily
average).
d) The choice of collector type;
 As is described above, the choice of collector mainly depends on 3 considerations;
i. Expected outcome in terms of energy collection.
ii. Space Available.
iii. Choice of temperature and associated equipment.
Several types are commonly used. (In order off increasing efficiency)
# Collector type Execution Remarks
1 Flat Plate An insulated box with an anti-
reflective glass cover where an
absorber plate is joined with a set of
tubes forming aninlet/outlet header.
The cheapest andmost simple type of
solar collector. Commonly used in
domestic water heating.
2 AdvancedFlat Plate An insulated box with double anti-
reflective glass covers where an
absorber plate is joined with a set of
tubes forming aninlet/outlet header
connected by tubes.
A better type than 1 since it is provided
with double glazing, addingadditional
insulation. Some panels are filled with
an inert gas. Some types can be used
as roof panels (S.O.L.I.D)
3 Evacuated tube (
heat-pipe)
A set of boronsilicate glass tubes that
are evacuated(vacuum) in which an
absorber plate with a heat pipe is
fitted. The condenser of the heat-
pipe gives its heat off in the (single)
header of the panel.
This type comes in many versions.
Tube diameter is important, with
greater diameters, more efficiency can
be expected. Comes in 48-55-60-70-
100mm tubes.
4 Evacuatedtube (u-
pipe)
A set of boronsilicate glass tubes that
are evacuated(vacuum) in which an
absorber plate with two pipes are
fitted. The pipes are directly
connected to inlet/outlet headers.
This type comes in many versions.
Tube diameter is important, with
greater diameters, more efficiency can
be expected. See above.
5 Evacuated tube
(concentrated)
Same as 3 and 4; However, at the
back side of the tubes, mirrors are
placedsothat the absorber benefits
from reflectedirradiationat the back
of the tubes.
The most efficient type if providedwith
u-tubes. Higher temperatures are
possible. (Upto 180 ⁰C.) A Sub-type is
the SydneyTube, a double tube design
with selective absorber.

3. June 30, 2014 SOLAR ASSISTED FACILITY COOLING
e) Sizing the array;
In order to arrive at a realistic figure regarding the size of the array needed for the purpose
defined out of a), b) and c), we need to approximate the yield per square meter by calculating
the efficiency of a particular panel. For this we need the following data:
(Data utilized must be either for absorber area or aperture area and nominal flow.)
1) Base efficiencyof the panel. Thisisthe efficiency when ∆T = 0 (TM-TA). Sometimes
called the conversion factor or optical efficiency.
2) Linear heat loss coefficient of the panel in W/m2.K
3) Quadratic heat loss coefficient of the panel in W/m2.K2
4) Global insulation. (Gd) in W/m2/d  derive G. Obtain data from Nasa Surface
Meteo or other reliable sources for the geographical location subject to the
calculation.
5) Ambient temperature.
6) Water inlet temperature.
7) Water outlet temperature.
When calculating the efficiency, the global insulation per day (Gd) is divided by available sun
hours and multiplied by ‘usable hours’, this gives G. Usable hours are the hours that the panel
can actuallytransfer energy to the circulating water. The figure derived from this calculation is
used to calculate average yield per m2 or per panel and consequently to size the array.
Note;dependingonthe time of dayand the temperatures aparticularpanel mightactuallyloose
energy, (Negative efficiency),soitisimportanttodefine the ‘0’yield time-frame of the panel in
orderto improve the accuracy of the calculation. The efficiency calculatedisanaverage figure as
well as is G.
A more precise methodispossible whenthe insulationperhourcanbe found. One possibility is
the MIDC-SOLPOSextra-terrestrial database; however the figures need processing before they
can be used.
f) Storage and associated methods of energy management.
Since the Sunis perdefinitionanintermittent source of energy from our perspective, there are
daysthat the expectedenergyharvestislowerthanwhatis needed. There are ways to mitigate
this situation in case a fixed part of the daily energy consumption must be met, as follows;
1) Install thermal energy storage tank. (water based TES) In each m3 of water 7 kWh of
energy can be stored at an approach temperature of 6 ⁰C (6-12⁰C) or ± 2 refrigeration
ton.
2) Convert a fire tank to TES tank. A common method, tank must be well insulated.
3) Make use of eutecticmaterials. (PCM).A relativelyexpensive but space saving method.
Phase Change Materials can store up to 10x more energy than chilled water.
--or--
Use conventional meanstogenerate the shortsupplied energy. Thisisthe mostcommonoption.
There will be days of oversupply.
The total targetvalue of harvestedsolar energy will be reached if the sizing of the array is done
basedon the lowestinsolationdata.Thismeansalargerarray and more unutilized solar energy.

4. June 30, 2014 SOLAR ASSISTED FACILITY COOLING
g) Presentation.
In order to overcome the usual hesitance that is apparent especially with operators of a
proposed system,we needtoclarifytoagreat extendthe insandoutsof applying a solar driven
application. This presentation should include the following elements:
1) An understandable technical explanation of the system.
2) A prediction of yields per month and year. (with reasonable reservations)
3) A simple ROI for the installation.
4) Benefits and drawbacks summarized or a SWOT analysis.
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Industrial applications.
Given the very high temperatures that can develop when collecting solar energy, it is evident
that industrial (HighTemperature) applications are in the realm of possibilities. In fact, several
industrial applications are already developed in high solar radiation areas around the world.
Example 1: Low pressure steam can be generated by a solar array consisting of parabolic
collectors. Heat transfer medium – water. Daytime operations.
Example 2: Power can be generated by a solar field consisting of solar tracking parabolic
collectors. Heat transfer medium molten salt. 24/7 operations. (Solar) Heat is transferred to
generate steamina highpressure heatexchanger,steamdrivesa turbine. The plant TES system
consistof two large saltsolutiontanks(swing-tanks),while one is discharging the other is filled
withreturningheatof thermal oil ora salt solution.The full tankwill be charged in the daytime,
while simultaneously the heat exchanger will be on-line for daytime steam production.
A very large array (1 of 3) with
a total electrical output of 600
MW. The total number of
mirrors is 350.000. Several
other plants are situated in this
region of the Nevada Desert.
The generator building and TES
tanks are situated at the center
of the facility.
A SHIP (Solar Heat In Industrial Processes) study commissioning by the European Union in
relationtosolarenergyutilizationmade clearthatof the total energy consumption in industrial
processesabout2/3 is inthe form of thermal energy while1/3 is in the form of electrical power
and lighting.The thermal component canbe cold, warmor hot water/air, steam or superheated
wateror veryhightemperature processes up to 300⁰C where metal-salts are utilized as energy
carrier.The table belowshowsa selection of processes and the temperature levels relevant to
those processes summarizing a Market Potential.

5. June 30, 2014 SOLAR ASSISTED FACILITY COOLING
MARKET POTENTIAL
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FDR June 2014
References: IEA TASK 33/IV