Proposition for the construction of a passive batch solar
water heating system with propane back up for
hospitals in Ghana
The goal of this proposition is to design a passive batch solar water heating system with
propane back up for the Nana Hima Dekyi District Hospital located in Dixcove, Ahanta
West, Western Region, Ghana. It is part of the alternative water system construction and
training project directed by the NGO African Health Net and funded by the European
Union. This design is also to be used on future proposed projects, hospitals or other
facilities in Ghana.
1 Design selection and description
The type of design selected for this proposal is the progressive tube batch solar water
heater. This design was selected for the following reasons:
-
Efficiency : Comparable with most commercially available units,
Low cost : Possibility of manufacturing with local materials available in Ghana,
Low maintenance : Very minimum maintenance required, panel built to last
Ergonomics : Relatively easy to build with basic tools and skills,
Unobtrusiveness: Made of one unit, easy to transport and mount on roof.
How it works:
The progressive tube solar water heater consists of a glass-covered panel that is highly
insulated. Solar radiation is absorbed by the panel through the glass cover by an absorber
plate that is made of aluminum and painted black to insure maximum efficiency.
The heat collector is made of copper tubing and is attached to this absorber plate. The
heat is transferred from the absorber plate to the copper tubing and then transmitted to the
water that flows through it. This progressive tube unit acts as a heat collector as well as a
storage tank.
As shown on the following Figure 1, hot water is drawn off the top of the unit and is
replaced by cold water that enters at the bottom of the collector each time hot water is
used.
1
Figure 1: Progressive tube solar batch water heating principle
The progressive tube solar water heater will serve as a preheat tank on more cloudy days
during the rainy season, but will be used as the mean heating system during the rest of the
year.
For the Dixcove hospital three solar heating units will be installed:
- Unit 1: Supplying the maternity ward, the theatre and the east wing of the main ward,
- Unit 2: Supplying the lab and the west wing of the main ward,
- Unit 3: Supplying the laundry room and the kitchens.
2
2 Purchase of raw material and itemized budget
For the construction of the solar panels, the materials can all be purchased locally. In the
table below, a list of the materials needed is shown as well as their provenance and cost.
This itemized budget corresponds to one unit.
(1 Ghanaian Cedi in US Dollars is 0.67363 for 4/27/2011)
REF
I
1.1
U
COST
GHS
COST
$US
Agona
18.00
3
0.50
30
$ 0.34
$ 20.21
$
$
6.06
60.63
Exterior grade plywood 4
mm thick, frame 8´ x 4´
Next Wavels
Takoradi
3
18
$ 12.13
$
36.38
Aluminium plate 0.5 mm
4´ x 8´ frame
Rockstered
LTD Takoradi
3
18
$ 12.13
$
36.38
Paint and wood
treatment
Primer for 48,8 m2
Matt black paint for 48,8
m2
Wood preservative coating
5 liters
Coralatey
Takoradi
1
45
$ 30.31
$
30.31
1
26
$ 17.51
$
17.51
1
40
$ 26.95
$
26.95
60
31
$ 20.88
$1,252.95
1
15.2
$ 10.24
$
3
50
$ 33.68
$ 101.04
3
20
$ 13.47
$
40.42
1
5
$
3.37
$
3.37
1
50
$ 33.68
$
33.68
DESCRIPTION
1.3
1.4
1.5
1.6
1.7
1.8
1.9
TOTAL
30 Gal solar batch water
heater
Panel tray + frame
2000 x 1000 x 100 mm
Teak wood sized 100 x 50
mm (linear meters)
Cutting by carpenter
1.2
Provenance
Agona
Copper tubing 1´´
diameter (linear meters)
Garden city
hardware
Takoradi
Aluminum foil 75 m x 30
cm
Supermarket
Takoradi
Float glass 5 mm 6´x 3´
frame
A2 Al Profile
Takoradi
Foam mattress for
insulation
water proof sealing
(Silicon)
screws, nails, wire, paint
brushes, tools, sand
paper,extras...
Takoradi
Takoradi
Hardware
shop
Takoradi
TOTAL SOLAR BATCH
WATER HEATER
10.24
$1,655.92
3
3 Construction of the solar panels
To enable the storage of 30 gallons of water for this project, one unit will consist of three
panels built in parallel connection as shown below in figure 2.
Figure 2: Three panels in parallel connection
3.1 Construction of panel tray and frame
The dimension chosen for the panels will be 2000 mm x 1000 mm x 100 mm. The wood
will be cut and machined accordingly to figures 3 and 4 below by the merchant.
Good corner joints are important to
insure good water proofing.
Figure 3: Corner joints
15
20 mm 15
mm mm
20 mm
40 mm
100 mm
2 pieces 100 x 50 mm
2 m long
50 mm
100 mm
40 mm
50 mm
2 pieces 100 x 50 mm
1 m long
Figure 4: Section details and sizes and of wood
4
This section will enable to put into place the absorber plate and the glassing inside the
frame.
After the frame has been constructed, two holes of 27 mm should be drilled in the side of
the frame to accommodate the copper tube inlet and outlet as shown in figure 2.
The wood beadings from the cutting of the sections will be kept for securing the absorber
plate and the glass sheet.
The sheet of plywood is then used for the backing sheet. It is measured and cut
accordingly before nailing it on the back of the frame as shown below in figure 5.
Figure5: Fixing backing sheet
The whole frame and backing sheet should now be coated with the wood preservative to
ensure a lasting finish.
3.2 Absorber plate
The aluminium plate will have to be cut to size and flattened out with a hammer as the
only material found for this purpose was the wavy aluminium sheets used for roofing.
The aluminium plate should be cleaned on both sides to remove any trace of oil that may
be present. The shiny side of the sheet will be sanded down to etch the surface. This will
remove small traces of oil and allow the paint to adhere to the surface better.
The primer will be applied before painting the sheet with the matt black paint.
5
3.3 Copper tubing
3.3.1 Shaping of copper tube
The next step is to produce the serpentined copper waterway tubing. If possible, 3 lengths
of 6 m will be used for each panel.
With care, the copper tube will be shaped by bending it around a cylindrical object like a
bottle. As copper is very soft metal it is easy to flatten or squash the tube when making a
bend without the aid of a forming machine, so it will be made sure to bend the tube
gradually. This will avoid kinking the pipe which could result in furring caused by
restricted water flow, thus reducing efficiency. If the pipe is kinked or squashed it is
possible to get it back into shape by placing it on a piece of wood and tapping it with a
wooden mallet. The tubes should be bent in as many bends as it can make.
The formed tubes will be painted with the matt black paint.
3.3.2 Attaching copper tube to absorber plate
When the paint is dry, the formed copper tube will be placed on top of the aluminium
absorber plate (black side). White chalk mark can be used to out the pattern of the copper
tubing onto the black absorber plate. A series of small holes will be drilled, two on either
side of the cross piece of tubing. These holes will take the wire that will hold the tube
closely against the absorber plate to achieve efficient heat transfer to the water in the
tube. The formed copper tube will be placed onto the plate and a good strong wire will
be thread through the holes and over the copper tube. A single piece of wire will be
sufficient. One end of the wire will be thread through a starting hole, over the tube, and
out through the second hole, this lacing process will be continued until the final hole is
reached and all of the cross pieces have been covered. The more loops the better- to give
good thermal contact between the copper tube and the absorber plate.
The copper tube can also be soldered to the aluminium sheet using special solder and flux
but the process has to be delicately controlled and will have to be done by a professional
solder.
Figure 6: Applying paint and fixing copper tubing to plate
6
The absorber plate is now ready for insertion into the panel tray, but first the insulation
must be in place.
3.4 Insulation
A 3" soft foam mattress will be cut to size and laid in the tray. This will compress when
the absorber plate is lowered on top of it like shown in figure 7.
Figure 7: Placing foam inside tray
A layer of aluminium baking foil will be sandwiched between the foam and the plate with
the shiny side to the plate. This will help stop heat loss by reflecting heat back to the
plate.
The absorber plate can now be inserted into the tray by making sure that the inlet and
outlet pipe ends are first bent back and then inserted through the 27 mm holes in the sides
of the panel as shown in figure 8. The plate will be held in place by the wood beadings
which will be screwed in the sides of the inner frame.
7
Figure 8: Placing in the collector plate
A final coat of matt black paint will be applied to mask any scratches on the paintwork
caused by the wire and to cover the inside wall of the wooden frame.
3.5 Inserting glazing sheet
The panel is now ready for glazing. 5 mm float glass is what was found in Takoradi for
this project although 4 mm is recommended for it’s slightly higher transmittancy.
The glass will be handled very carefully and will be delivered by the glazier if possible.
The inside of the frame will be measured accurately and the glass will have to be cut to
exact size by the glazier. There should be a gap of 10 mm between the top of the copper
piping and the cover as shown in figure 9. A larger gap will result in lower efficiency.
After the glass is placed in the tray, it will be secured with wood beading and a good
sealant like silicon will be used to keep out moisture.
Figure 9: Cross section of solar panel
Now that the panels are constructed they should be stored in a safe place until required.
They should be stored upright so that the tube inlets and outlets will not be damaged.
The panels will be heavy and help should be obtained when moving them
3.6 Installing the panels on the roof
The Dixcove Hospital offers elements of the rooftops which are horizontal and made of
thick concrete. These will be perfect for installing the solar panels. These locations are
shown in the following pictures:
8
Unit 1: Maternity, Theatre, main ward east
Unit 2: Lab, main ward west
Unit 3: Laundry room and kitchens
Figure 10: Pictures of the location for the 3 solar heating units
The panels will be installed horizontally for maximum sun collection at this latitude,
although a slight slope facing south will be taken into account to enable rainwater runoff.
Four treated wood blocks (2 blocks of 150 mm x 150 mm x 60 mm and 2 blocks of 150
mm x 150 mm x 40 mm) will be attached to each corner of the panel using stainless steal
brackets. The two thickest ones will be attached to the northern corners; this will give the
panels a slight slope so that the rainwater can runoff. This will also allow a gap of 60 to
40 mm between the panel and the top of the roof which will avoid potential stagnating
rainwater being in contact with the wooden frame.
The wood blocks will then be bolted into the concrete.
The principle of the roof fixing for the panels is shown in figure 11 below:
9
Wood
block
Roof
Stainless steal bracket
Figure 11: Fixing panels to the roof
4 Connection with the propane back up water heaters
Propane water heaters will be installed as a back up for the solar heating systems. For
each of the solar units one tank will be installed as closest as possible to the solar panels
and in convenient locations where the hospital staff will be able to operate them when
necessary.
4.1 Location for the heating tanks
- Unit 1: The tank can be installed in replacement of the old tank in the pharmacy where
the plumbing is already accessible.
- Unit 2: The tank can be installed in a corner of the room adjacent to the lab.
- Unit 3: The tank can be installed in replacement of the tank in the kitchens where the
plumbing is already accessible.
Location for the first two tanks can be seen in the following figure 12:
Figure 12: Locations for propane water heating tanks respectively in pharmacy and Lab
10
4.2 Description of the connection with the tanks
Copper tubing of 1/2” diameter will be used for the connecting, thus 1” to 1/2” reducers
will have to be used at the inlets and outlets of the panels. The tubing used for the
connection will have to be highly insulated to prevent heat loss from the water running
through the solar panels to the tanks.
The connection between the solar panels and the propane water heater will be
manufactured as shown in the figure 13:
1 - Supply Shutoff Valve
2 - 3-Way Ball Valve
3 - 2-Way Ball Valve
4 - Tempering Valve
5 - Boiler Drains
6 - Pressure Relief Valve
7 – Conventional Gas Water Heater
8 - Temp/Pressure Relief Valve
9 - Roof Jacks
10 - Progressive tube batch heater
Hot water
out
Cold water
in
Figure 13: Connection system features
The different components needed for the connection system are described in figure 14:
1 - Cast Bronze “T” Fitting (1/2”) x2
2 - Full Port 3-Way Ball Valve
3 - Full Port 2-Way Ball Valve
4 - Anti Scald Valve
5 - Pressure Relief Valve
6 - Bronze Boiler Drain (x2)
Figure 14: Connection system components
11
4.2 Itemized budget for connection system
In the table below, a list of the components needed is shown as well as their provenance
and cost. This itemized budget corresponds to one unit.
REF
II
DESCRIPTION
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
U
COST
GHS
COST
$US
TOTAL
Fanco
KUMASI
1.00
200.00
$ 134.73
$ 134.73
30 Gal propane water
heater
30 Gal propane water
heater
III
Provenance
Piping and fixtures
Cast Bronze T-Fitting
(1/2”)
Full Port 3-Way Ball
Valve
Full Port 2-Way Ball
Valve
Anti Scald Valve
Pressure Relief Valve:
150psi
Bronze Boiler Drain (x2)
Temp/Pressure Relief
Valve
Copper piping 1/2",
linear meters
PVC piping, linear
meters
1" to 1/2" copper tubing
reducer
50
TOTAL PIPING AND
FIXTURES
12
$
-
$
-
$
-
$
-
$
-
$
-
$
$
-
$
$
-
$
-
$
-
$
8.08
$ 404.18
$
-
$
-
$
$
-
$
$
-
$ 538.90
References:
1 David A. Bainbridge, The Integral Passive Solar Water Heater Book
2 Professor Ashok Gadgil, Domestic Solar Water Heater for Developing Countries
3 Build Your Own Solar Water Heating Panel, www.bigginhill.co.uk/solar.htm
4 Thermal conversion technologies, ProgressivTube passive solar water heater
12