Designing Solar Thermal Systems

Designing Solar Thermal System

Introduction •

• • •

•

Before we start discussing the designing of solar thermal systems we need to know the concept of a system. My definition of a system is a combination of equipment and devices which have been put together to perform a certain predetermined function. If we accept this definition, a system has to have a function to perform and it has to have equipment and devices to perform that function. In case of Solar Thermal Systems the function to be performed is some variant of delivering heat for an application. The system has the input in the form of available solar radiation and output in the form of heat. The basic of the solar thermal system thus consist of input device which will convert the solar radiation to heat and a combination of other equipment or other devices to output this heat into useful form. The most common input device for Solar thermal system has been Solar Flat Plate collector and I have so far done most of design based on this device and will follow this for the designs being discussed. The underlying principals of the design however can be used for other devices also with adjustments according to the nature of these devices. Even in flat plate collectors the collectors used to heat liquids are the most common ones and most design aspects discussed will relate to this type of flat plate collectors.

Application of Solar Thermal Systems •

For any system design to be taken up we have to consider the intended heat output from the Solar system. • The most common form of heat output has been the in the form of hot water delivered in a temperature range suitable for various uses. This covers all applications which deliver hot water as a final product. • Another form of heat output is to provide heat to maintain temperature of some reservoirs at certain specified temperatures. This covers all systems used for heating swimming pools or electroplating/ metal processing baths. • Other type of systems deliver heat to air but using liquid collectors. The systems for drying and systems for space heating come in this category.

Solar Hot Water systems •

•

•

•

This application has been the most popular application so far and 95% of systems installed in the country probably belong to this category. The installation of systems for this purpose was stated long time back and I had felt that all concerned people have understood every aspects of design of these systems. But recently it so happened that a company with more than 15 years of experience in this field had come to me as they were facing problems during commissioning of the system. I found that the most of the components of the system were mismatched. The piping connections were not designed but arbitrarily made as per the decision made by the supervisor at site. It almost became clear that the organisation has not understood the concept of design and need for the design of such a system. This has been happening repeatedly with most of the organisations in this field. This practice came into existence as the engineering aspects of Solar Thermal Systems has been neglected under the mistaken belief that these systems are too simple and do not require any engineering effort. My attempt at this time will be to remove that feeling and introduce some aspects of engineering required for these systems. Also I will give details of some of the Solar systems for which I had provided the engineering details.

Thermosyphon Solar Water Heating System •

In these systems arrangement of Solar collectors and Storage Tank/Heat Exchanger and connecting pipes is such that the flow of fluid takes place due the density differential of hot and cold fluid and no prime mover is provided in the system for mass flow. • These systems have been the ones most misunderstood for the requirement of engineering inputs. Feeling in the industry and other people concerned has been almost like asking “What do you mean by Engineering of Thermo-syphon system” or that nothing is required to be done in a thermo-syphon system and you have solar collectors, a storage tank and you connect these with some piece of pipe and the system starts working. • I shall attempt to some how remove this feeling and try to explain how each element of the system behaves in such a system. • I shall start with the smallest of these system( the single collector solar system) and also show you the larger systems which have been engineered and successfully operating for number of years.

Single Collector Thermosyphon System

Calculation of Thermo-syphonic Head

Thermosyphonic Head Calculations Distance Angle Header to Collector Header Mtr Deg 1.9 43

Height Height Header to Header Header Tank inlet Mtr Mtr 1.296 0.15

Height Tank inlet to outlet Mtr 0.33

Temp collector top Deg C 60

Water Temp Water Differential Density Tank Density Head at Temp Bottom at Temp Kg/Cub M 983.2 20 998.2 14.44

1.9

43

1.296

0.15

0.33

50

988.1

20

998.2

9.73

1.9

43

1.296

0.15

0.33

45

990.6

20

998.2

7.32

1.9

43

1.296

0.15

0.33

40

992.1

20

998.2

5.87

1.9

43

1.296

0.15

0.33

35

994

20

998.2

4.04

1.9

43

1.296

0.15

0.33

30

995.7

20

998.2

2.41

1.9

33

1.035

0.15

0.33

60

983.2

20

998.2

12.49

1.9

33

1.035

0.15

0.33

50

988.1

20

998.2

8.41

1.9

33

1.035

0.15

0.33

45

990.6

20

998.2

6.33

1.9

33

1.035

0.15

0.33

40

992.1

20

998.2

5.08

1.9

33

1.035

0.15

0.33

35

994

20

998.2

3.50

1.9

33

1.035

0.15

0.33

30

995.7

20

998.2

2.08

1.9

25

0.803

0.15

0.33

60

983.2

20

998.2

10.75

1.9

25

0.803

0.15

0.33

50

988.1

20

998.2

7.24

1.9

25

0.803

0.15

0.33

45

990.6

20

998.2

5.45

1.9

25

0.803

0.15

0.33

40

992.1

20

998.2

4.37

1.9

25

0.803

0.15

0.33

35

994

20

998.2

3.01

1.9

25

0.803

0.15

0.33

30

995.7

20

998.2

1.79

Pressure Loss Calculation for Flows Pressure Drop Calculations Single Collector Configuration Flow Rate Dia Ltre/Hr CM

Velocity M/Sec

Vh Avr V mm Water M/sec

Travel L M

Header Riser Pipe 15

10 1.11 10

2.36 1.128 1.6

0.0064 0.0031 0.0138

0.0202 0.0048 0.0954

0.0032 0.0031 0.0138

Visc at40 Reynld No f sqM/s X 10 P(6) 2.2 0.657 228.1 1.8 0.657 53.0 4 0.657 336.5

Friction p mm Water

Delta P mm Water

Header Riser Pipe 15

20 2.22 20

2.36 1.128 1.6

0.0127 0.0062 0.0276

0.0806 0.0191 0.3817

0.0064 0.0062 0.0276

2.2 1.8 4

0.657 0.657 0.657

456.2 106.1 672.9

0.068 0.098 0.062

0.0030 0.0034 0.0947

0.08 0.02 2.39

Header Riser Pipe 15

30 3.33 30

2.36 1.128 1.6

0.0191 0.0093 0.0414

0.1815 0.0429 0.8589

0.0095 0.0093 0.0414

2.2 1.8 4

0.657 0.657 0.657

684.3 159.1 1009.4

0.062 0.089 0.056

0.0062 0.0069 0.1926

0.19 0.05 5.35

Header Riser Pipe 15

40 4.44 40

2.36 1.128 1.6

0.0254 0.0124 0.0553

0.3226 0.0763 1.5269

0.0127 0.0124 0.0553

2.2 1.8 4

0.657 0.657 0.657

912.4 212.1 1345.8

0.057 0.083 0.052

0.0102 0.0114 0.3187

0.33 0.09 9.48

Header Riser Pipe 15

50 5.56 50

2.36 1.128 1.6

0.0318 0.0154 0.0691

0.5041 0.1192 2.3859

0.0159 0.0154 0.0691

2.2 1.8 4

0.657 0.657 0.657

1140.5 265.1 1682.3

0.054 0.078 0.049

0.0151 0.0168 0.4709

0.52 0.14 14.79

Header Riser Pipe 20

30 3.33 30

2.36 1.128 2.16

0.0191 0.0093 0.0227

0.1815 0.0429 0.2586

0.0095 0.0093 0.0227

2.2 1.8 4

0.657 0.657 0.657

684.3 159.1 747.7

0.062 0.089 0.060

0.0062 0.0069 0.0625

0.19 0.05 1.61

Header Riser Pipe 20

50 5.56 50

2.36 1.128 2.16

0.0318 0.0154 0.0379

0.5041 0.1192 0.7183

0.0159 0.0154 0.0379

2.2 1.8 4

0.657 0.657 0.657

1140.5 265.1 1246.1

0.054 0.078 0.053

0.0151 0.0168 0.1528

0.52 0.14 4.46

Header Riser Pipe 20

90 10.00 90

2.36 1.128 2.16

0.0572 0.0278 0.0682

1.6331 0.3863 2.3273

0.0286 0.0278 0.0682

2.2 1.8 4

0.657 0.657 0.657

2052.9 477.2 2243.0

0.047 0.068 0.046

0.0422 0.0470 0.4275

1.68 0.43 14.39

Header Riser Pipe 25

90 10.00 90

2.36 1.128 2.72

0.0572 0.0278 0.0430

1.6331 0.3863 0.9255

0.0286 0.0278 0.0430

2.2 1.8 4

0.657 0.657 0.657

2052.9 477.2 1781.2

0.047 0.068 0.049

0.0422 0.0470 0.1801

1.68 0.43 5.73

Header Riser Pipe 25

145 16.11111 145

2.36 1.128 2.72

0.0921 0.0448 0.0693

4.2391 1.0028 2.4024

0.0460 0.0448 0.0693

2.2 1.8 4

0.657 0.657 0.657

3307.5 768.9 2869.7

0.042 0.060 0.043

0.0972 0.1083 0.4149

4.34 1.11 14.83

0.081 0.117 0.074

0.0009 0.0010 0.0282

0.02 0.01 0.60

Thermo-syphon Head Calculation for 5 Collectors System Thermosyphonic Head Calculations 5 Collector System Distance Angle Header to Collector Header Mtr Deg 1.9 43

Height Height Header to Header Header Tank inlet Mtr Mtr 1.296 0.15

Height Tank inlet to outlet Mtr 0.8

Temp collector top Deg C 60

Water Temp Water Differential Density Tank Density Head at Temp Bottom at Temp Kg/Cub M 983.2 20 998.2 17.97

1.9

43

1.296

0.15

0.8

50

988.1

20

998.2

12.10

1.9

43

1.296

0.15

0.8

45

990.6

20

998.2

9.10

1.9

43

1.296

0.15

0.8

40

992.1

20

998.2

7.31

1.9

43

1.296

0.15

0.8

35

994

20

998.2

5.03

1.9

43

1.296

0.15

0.8

30

995.7

20

998.2

2.99

1.9

33

1.035

0.15

0.8

60

983.2

20

998.2

16.01

1.9

33

1.035

0.15

0.8

50

988.1

20

998.2

10.78

1.9

33

1.035

0.15

0.8

45

990.6

20

998.2

8.11

1.9

33

1.035

0.15

0.8

40

992.1

20

998.2

6.51

1.9

33

1.035

0.15

0.8

35

994

20

998.2

4.48

1.9

33

1.035

0.15

0.8

30

995.7

20

998.2

2.67

1.9

25

0.803

0.15

0.8

60

983.2

20

998.2

14.27

1.9

25

0.803

0.15

0.8

50

988.1

20

998.2

9.61

1.9

25

0.803

0.15

0.8

45

990.6

20

998.2

7.23

1.9

25

0.803

0.15

0.8

40

992.1

20

998.2

5.80

1.9

25

0.803

0.15

0.8

35

994

20

998.2

4.00

1.9

25

0.803

0.15

0.8

30

995.7

20

998.2

2.38

Deciding Design Parameters for Thermo-syphon Solar Water Heating System The design parameters for thermo-syphon solar water heating systems can be decided with the following The solar heat is be collected on as when available basis. The use pattern will be as and when required basis. There will be need for matching these requirements. This can be done by using a storage device in the form of Hot Water storage Tank.. The Capacity of the Hot Water Tank is decided to balance the chronological mismatch between the supply and the demand. When solar heating is available and demand also exists the system must be in a position to deliver the heat. This condition imposes a restriction that generation must be at the required or higher than the required temperature. Supposing we are designing a system with capacity of tank equal to the demand of hot water say at a temperature 60 Deg C. Also water below 45 deg C will not be useful and we have the requirement during the day also. If a system of 100 litre capacity is designed for flow rate of 50 litre/hr. The tank will get heated to 60 Deg C in 6 hrs of sunny period but it will require 3 circulations for the temperature to be built up .Which means temperature at the top of the tank will lower than required after first circulation of tank water through the collector. This means water at useful temperature will be available only in the afternoon period after previous days heating has been used up. However if circulation rate is to be between 20-30 litre/hr , water reaching the top of the tank is at useful temperature in the first circulation itself and it is instantly available. We are able to decide tank capacity and water flow rate accordingly.

Deciding Design Parameters

After deciding the capacity of storage tank. We have to decide other design parameters of the tank. The operating and design pressure of the storage tank and tank material. The design pressure is the expected highest operating pressure of the system and the material of the tank is decided by the compatibility of the material with the quality of water being used . The seasonal variation in demand decides the optimisation of the collector tilt. The temporary hardness level of water decides whether the system can be direct heating type or indirect heating type with heat exchanger to be built in the circuit. Heat exchanger can also be used to isolate collectors from the high pressures on the use side. If heat exchanger is required it's capacity should be such that at the required flow rate can be maintained and the heat can be transferred without raising the collector outlet temperature significantly. Having decided these parameters and also the routing of the collector piping we can calculate and chose the pipe sizes which will be suitable for providing the desired flow rate.

Examples of Thermo-sysphon Solar Water Heating System Design

Examples of Thermo-sysphon Solar Water Heating System Design

Example of Thermo-syphon Solar Water Heating System

Examples of Thermo-sysphon Solar Water Heating System Design

Examples of Thermo-sysphon Solar Water Heating System Design Heat Exchanger for 6000e system at 60 Deg C

Examples of Thermo-sysphon Solar Water Heating System Design Heat Exchanger for a 2500 Litre capacity System at 60 Deg C

Examples of Thermo-sysphon Solar Water Heating System Design Layout for System at IIC

Examples of Thermo-sysphon Solar Water Heating System Design Tank with Heat Exchanger on Supply Side 10000 lpd System at IIC

Examples of Thermo-sysphon Solar Water Heating System Design 10000 lpd System at Kautlya Inndustries Gurgaon

Designing Solar Thermal Systems with Pumps • • • • • • •

• • •

It has been possible to design and install large capacity thermosyphon systems. Some of these are 10000 lpd system at Andhra Bhavan intalled in 1997 10000 lpd system at Kautlya Indutries Gurgaon 10000 lpd system at IIC for kitchen use However at times it becomes necessary to design and instal systems with prime movers. In designing such systems we have to first decide the design parameters of the system The design starts with determining the no of collectors and their orientation, also determining the storage capacity required. Decision regarding the need for Heat exchanger is to be made for the system. Based on the requirement and performance optimisation the flow rate is determined. Collector Layout is decided on the place availability and orientation. Interconnecting piping is then decided based on flows in different collector banks. After this calculations for pressure drops calculations can be made and pumps can be chosen for the primary side and secondary side

Example of Design Parameters for Solar Thermal system with pumps SOLAR HEATING SYSTEM For ULTRA forKeeping the drums Open Bath of Size of Size 5x1.1x1 mtr operating Temperature 55+-2Deg C BOM and specifications Operating 24 Hrs with covers removed only for loading and unloading (covered during nonoperating period) ITEM SPECIFICATION 1 Solar Collectors Copper-copper 2Sq meter each selectively coated High temperature application 2 Hot water Baths Insulated

QUANTITY 80

5mtr x 1.1mtr x 1mtr filled upto 0.7 mtr when without drums upto 0.9 mtr with drums capcity 6 drums each 2 nos

3 Loading Arrangement

Monorail beam with 1 ton hoist for loading and unloading 2 nos

4 Pallets for drum

S S pallets of capacity 500 kg for 200 Kg drums

5 Supports for collectors

Angle iron supports properly fixed to the roof for fixing solar collector to the roof at 43 deg to horizontal, painted with 2 coats of primer and 2 coats of paint For 80Collectors 6000 l[tre Capacity MS vertical insulated

6 Hot Water Storage tank

7 Interconnecting Piping

8 Piping from pool to Heat Exchanger 9 Pumps

10 Electric/Gas Back up

11 Control Panel 12 Instruments 13 Bath cover

12 nos

Piping for connecting solar collectors and and Storage tank litres/hr GI Medium class piping to BIS standard All piping to be insulated with glass/rock wool of 48kg/cubic meter of approprate thickness and clad with aluminium cladding

Estimated qauntities

30Kw fitted in storage tank of 1000 Litres MS tank of 4 mm thickness painted with polyurethene based paint with thermostatic controls. Heating elements to be sutable for chlorinated water. DTC control for primary as well secondary loop and thermostac control for Electric Back up Temperature and pressure gauges and DTC sensors Bath cover of 6Sq meter

1 no

40NB-50Mtr 32 NB-50meters 25NB -30 Metres Estimated qauntities Insulated Piping to GI Medium Class as per BIS standard 40NB- as per site Approx-20 M For flow rate of 4000 litre/hr at operating conditions Kirloskar Make 4 nos.

1 Set 1Set 2 nos 1Set

14 Makeup /Expansion Tank 500 litre capacity Sintex /MS tank

1 No

Example of Design Parameters of Solar Thermal System with Pumps

SOLAR HEATING SYSTEM FOR Imreial Hotel 60 Deg C BOM and specifications Ouput will vary from 19000litres /day to 24000 litres/day onclear sunny days in different seasons operating Temperature60 Deg C ITEM 1 Solar Collectors

2 Heat exchanger

SPECIFICATION

QUANTITY

Copper-copper 2Sq meter each selectively coated conforming to BIS specifications and BIS marked

200

Tube and Tube type SS Drawing to be provided later For Flow rate of 4000 litres /hr

1 3 Supports for collectors

4 Interconnecting Piping

Angle iron supports properly fixed solar collector at 43 deg to horizontal, painted with 2 coats of primer and 2 coats of paint

For 200Collectors

Intter coneecting Piping for thermosyphon Mode

Estimated qauntities 25 nb-50Mtr 50NB -200Mtr 40NB-200Mtr

5 Piping from Storage Tank to Heat Exchanger

50NB 100 Mtrs approx

6 Pumps

4000 litre/hr at 2.5KG/ sq Cm

4 nos

7 Storage Tank

25000 litres MS 6mm thick Shell and 10MM bottom 1No and 6mm conical top Vertical tank at basement ground level

8 Control Panel

DTC control for primary and themostac control for secondary loop Temperature guage,DTC,Pressure Gauge and Themostat

9 Instruments

1 Set 1Set

Example of Design Parameters of Solar thermal System With Pumps SOLAR HEATING SYSTEM FOR SWIMMING POOLS at Chandigarh 24.69x16.15 mtr BOM and specifications Hours of Operation 12Am-4Pmfrom Dec, Jan & Feb, and 9Am-7Pm in March,Oct, Nov Alternately 5 PM to 8 PM in Dec ,Jan, Feb Avoid using during windy period to avoid cooling and chill effect of wind on swimmers 25+-2 Deg C Operating Temperature ITEM

SPECIFICATION

QUANTITY

1 Solar Collectors

Copper-copper 2Sq meter each selectively coated conforming to BIS specifications and BIS marked

2 Heat exchanger

Titanium Plateor SS Tube and tube type with flow rate of 7000 Litre /hr in in primary and secondary loops with primary temperature of 45 and 35 deg centigrade and seconadary temperature of 35 and 25 deg centigrade.Capable of withstanding pressure of 10Kg/sq cm and gaskets designed for 100deg c and chlorinated water.Pressure Drop not to Exceed 1Kg/Sqcm Angle iron supports properly fixed solar collector at 46 deg to horizontal, painted with 2 coats of primer and 2 coats of paint For 80 Collectors

3 Supports for collectors

4 Interconnecting Piping

5 Piping from pool to Heat Exchanger 6 Pumps

7 Gas/Electrical Back up if required

8 9 10

11

Piping for connecting solar collectors and heat exchanger primary Loop and pump for flow rate of 7000 litres/hr GI Medium class piping to BIS standard All piping to be insulated with glass/rock wool of 48kg/cubic meter of approprate thickness and clad with aluminium cladding Insulated Piping to GI Medium Class as per BIS standard For flow rate of 7000 litre/hr at operating conditions Kirloskar Make

80

1

Estimated qauntities Average 40NB-200M 50NB 40NB 25 NB. Estimated qauntities 50NB-? Meters As per Site 4 nos.

60Kw fitted in storage tank of 1000 Litres MS tank of 1 no 4 mm thickness painted with polyurethene based paint with thermostatic controls. Heating elements to be sutable for chlorinated water. Control Panel DTC control for primary as well secondary loop and 1 Set thermostac control for Electric Back up Instruments Temperature and pressure gauges and DTC sensors 1Set Pool cover Pool cover for pool of 400Sq meter with a trolley for transporatation and handling of pool cover. Pool cover to Transparent but opaque to infrared. It should be 1Set suitable for tying at the ends to avoid being blown away by winds Makeup /Expansion Tank 250-300 litre capacity Sintex /MS tank 1 No

Solar Water Heating System with Heat Exchanger and Pump

Schematic Arrangement for an Electroplating Bath Heating

Schematic Arrangement for a Swimming Pool Heating System

Heat Exchanger for a Swimming Pool

Schematic for Drying Application Using Liquid Collectors