Mechanical Engineering Project: Solar Water Heating Design for Villa

This project report details the design of an active, closed-loop solar water heating system for a villa in Beirut, Lebanon. It begins with an introduction to solar water heating, its benefits, and the different types of systems, including direct and indirect systems, and flat plate and evacuated tube collectors. The report outlines the design methodology, including the estimation of hot water storage tank capacity based on daily demand, the calculation of average solar radiation for representative months, and the sizing of the flat plate collector. Performance parameters like effectiveness are calculated. The report also covers pump power estimation, considering pipe length, diameter, and bends. Assumptions are clearly stated. The objective is to design a system for a villa with an occupancy of six persons. The report includes sketches, diagrams, equations, and tables summarizing key findings and comments on the system's ability to meet hot water demands in all seasons. The report also discusses potential yearly electricity savings.

Solar Water Heating Design 1
SOLAR WATER HEATING DESIGN
Student’s Name
Course
Professor’s Name
Institutional Affiliation
City
Date

Solar Water Heating Design 2
Introduction
Background
In the past, the human being has invented and designed different water heating techniques
for use at home and commercial level. Since the beginning of the twenty-first, water heating for
domestic use in many countries is being done by solar. This is as opposed to heating water by
electricity or other fossil fuels. Solar water heating lowers the electricity bills by up to 30%
(Wang, Yang, Qiu, Zhang, X. and Zhao 2015)
Solar water heating is among the Standard Development Goals (SDGs) that govern the
way people use energy. Global warming resulting from greenhouse gas emission has been a day
to day subject that is being discussed all over the world and among the solutions to curb the
effect is use of renewable energy. Traditional water heating for domestic applications used
boilers that rely on fossil fuels. The carbon monoxide, sulfur oxide, water vapor, among other
end products of the combustion process have accumulated in the atmosphere thus leading to the
global warming effect. Replacing the conventional water heating will mean that the rate of
greenhouse gas release is minimized.
Typically, an operational solar water heating system requires a solar collector panel, hot
water storage tank, cold or reserve water storage tank, control kit, and at times a circulator pump.
Some collector panels are normally mounted on the flat roof terraces of buildings by means of
frames while others are mounted on pitched roof and do not require mounting frames.
Theory
There are basically two types of solar water heating systems, direct and indirect systems.
Further, the systems are classified further into integrated and split systems. In an integrated solar
water heating system, the hot water storage cylinder and the solar collector panels are located on

Solar Water Heating Design 3
the roof level of the building. This system is mostly used in houses with low height so as to
minimize the thermal losses. In a split system the collector panels are located on the roof level
while the hot water cylinder is located inside the house. This system is normally applied in high
rise buildings where the expected thermal loses are high. Each system has pros and cons. For
instance, the integrated system does not require a lot of pipework between the hot water cylinder
and the solar collectors. This saves on pipework cost. On the other hand, this system is only
applicable to low rise buildings. The split system is cheaper when installation is done on high
rise buildings but the system is much expensive as there is a lot of pipework associated.
In direct or open-loop solar water heating, only water is circulated in the system. This
system may require a circulation pump depending on the type of installation. Collector panels get
heated from the sun irradiation and heat is transferred into the water by means of conduction, and
convection. This system is also referred to as a thermal siphonic or natural system. The water is
then conveyed to the hot water cylinders from where it is drawn to the point of use. In this
system, there is no heat exchanger required and this makes this system cheaper as compared to
indirect solar water heating. This system is also used in swimming pools and the water flowing
in the system is the water coming out of the faucets.

Solar Water Heating Design 4
Figure 1: Direct/Open-loop Solar water heating system (http://grantengineering.ie)
One of the advantages of the open-loop system is that it is less expensive as no heat
exchanger is required at any given point. The system is also easy to add to an existing system
without the procurement of additional parts or assemblies. This system is also very efficient as
there is less heat loss and it is effective in warm climates such as Beirut where freezing
conditions are rare. On the other hand, this system can freeze in cold climate an thus the system
is only limited to hot climates. The controls for this system need to be monitored from time to
time as the system can overheat. When the system is left unused for long durations, the pipes do
not completely drain and this may introduce bacterial growth as well as rusting and corrosion.
Compared to the other systems, this system is expensive in repair and maintenance.
In closed or indirect solar water heating, thermal fluid is circulated between the solar
collector panel and the hot water cylinder. The most common thermal fluid is glycol which is an
anti-freeze liquid that has a very low boiling point. In the collector panel, the glycol is heated

Solar Water Heating Design 5
from the sun irradiation. The hot fluid is then circulated by means of a circulator pump to a heat
exchanger located in the hot water storage cylinder. In the hot water cylinder, the inlet receives
cold water at room temperature. The glycol exchange heat with the water and in the process, hot
water rises to the top of the cylinder from where it is conveyed to the point of use. The glycol is
forced back to the collector panel to receive more heat. There is no mixing between the glycol
and domestic water.
Similar to open loop, this system is applicable to domestic or household use as well as
commercial use. When used for swimming pool heating, the system prevents pool water which is
saturated with salts and other minerals from getting into contact with the solar collector panels
which may be corroded and hence reducing the performance.
Figure 2: Indirect/ Closed-loop solar water heating system (http://grantengineering.ie)

Solar Water Heating Design 6
The closed-loop has the advantage over the open system as no freezing is expected as
well as overheating on the system is very minimal as glycol circulation control is simple. This
system works perfectly even at cooler climates where freezing is expected. It is also easier to
drain the pipes when the system is not in operation. On the other hand, this system needs the
owner to purchase antifreeze from time to time. This system is also expensive as it includes a
heat exchanger and the system is difficult to fit an existing system.
Solar Collector Panel
There are basically two types of solar collector panels. One that heats liquid and the one
that heats air. Flat solar collector panels contain absorber plates made from high thermal
absorbing capacity that is covered with a black surface. There is also a transparent cover on the
outer part of the panels that trap in long-wave radiations (Sharif, Al-Abidi, Mat, Sopian, Ruslan,
Sulaiman, and Rosli 2015). The main purpose of the transparent cover is to reduce heat loss by
convection. Flat plate collectors can heat up the water up to 95 degrees Celsius but are normally
limited to 60 degrees Celsius. The flat type of collector panels is cheap in construction with low
initial installation costs and no movable parts. This ensures that the system is durable and easy to
repair. One key advantage of these panels is that they also absorb diffuse radiation during cloudy
days thus making the system more efficient.

Solar Water Heating Design 7
Figure 3: Flat solar collector panel (http://grantengineering.ie)
The other type of collector panels is the evacuated tubes collector. This type of solar
collector is made from evacuated tubes that are joined to a common header or manifold where
the heat transfer takes place. These tubes often have a heat pipe that helps in heating the water.
Each evacuated tube is treated as a collector panel on its own and this makes these collectors
more efficient than the flat plate collectors.
Figure 4: Evacuated Solar collector panel (http://grantengineering.ie)

Solar Water Heating Design 8
Storage tanks
How water cylinders are used to store hot water for domestic use. They come in various
sizes ranging from 100 litres, 120 litres, 150 litres, 200 litres, 300 litres, and 600 litres. Large
capacity cylinders are normally housed in the house or on plinths outside the house while those
of low capacity are located on the roof. The cylinders can either be vertical or horizontal
depending on the system design, space allocated as well as the intended aesthetics. These
cylinders are further classified into two; thermosiphon and forced circulation. Thermosiphon
cylinders are normally located just above the collector panels. The property of hot water is that it
is less dense than the cold water and therefore rises to the tank and drawn at the top section of the
tank. Forced circulation hot water storage cylinders can be located on the ground level as the
pump helps in circulation.
As a contingency plan, electrical heating elements are integrating with the cylinders so as to aid
in heating the water when the solar irradiation is low for instance during the night or rainy
seasons. The heating elements are normally of 2 kilo Watts.
In addition to the heating element, the hot water storage cylinders are provided with
expansion tanks as well as safety valves for pressure and air release. These are critical integral
parts of the solar water heating system.
Pipework
The pipework used for hot water conveyance from the hot water cylinder to the point of
use, as well as thermal fluid circulation pipework, is normally insulated so as to minimize the
heat losses. In recent years, steel and copper pipes have seized to be used as they are associated
with corrosion and impurities that are hazardous to human consumption. Glass fibre reinforced
PVC pipes are being used as these pipes do not corrode with water. The pipes also have excellent

Solar Water Heating Design 9
thermal insulation and thus low heat losses are experienced with these pipes. It is important for
the plumber and the solar water heating technicians to note the pressure requirements for the
pipes used to reticulate the hot water as well as glycol as exceeding the pressures would bust the
pipes.
Figure 5: Fiberglass reinforced PPR pipes (http://grantengineering.ie)
Controls
Temperature and flow controls are the main parameters for the control needed on solar
water heating. It is important to maintain optimal temperatures so as to avoid overheating of the
system. Flow control normally monitors the flow of thermal fluid within the system. Fifth-
generation controls are being used nowadays that help to control the entire system remotely
using mobile devices. In addition to smart control, thermostatic mixing valves are still used to
regulate the hotness or coldness of the water.

Solar Water Heating Design 10
Figure 6: Solar Controller (http://grantengineering.ie)
Solar Water Heating Design
In this project, the closed-loop system is considered where the collector panel is located
on the roof while the hot water cylinder is located in the villa on a proposed location by the
Services Engineer. The thermal performance of the solar water heating is defined by the system
effectiveness that is given by the below series of equations.
The solar fraction is based on the experimental assessment of the area that the system is
being installed. In Lebanon, for instance, the solar fraction which is typically the amount of

Solar Water Heating Design 11
energy provided and the effectiveness of the collector relative to the total amount of energy that
the installation requires is 82%. As a rule of thumb, 30 litres of hot water demand is taken as
typical for domestic application.
The collector area is calculated from the below equation.
The circulator pump is sized depending on the head and flow requirements on the
installation. Typically, the head is the vertical length of pipework between the cylinder and the
collector panel. The flow rate is determined from the average consumption depending on the
flow rate required at the faucets outlets. The circulator pump is normally located on the cooler
side of the glycol line. The pump is controlled by the central controller unit and thus regulating
the flow of the glycol depending on the hot water demand.
Objective
The objective of this report is to design a solar water heating system for a Villa in
Lebanon, Beirut. The scope of the design covers hot water cylinder sizing, solar collector panel
as well as circulator pump sizing.

Solar Water Heating Design 12
Assumptions
There are a couple of assumptions made to the solar water heating system. First, the
system is assumed to work throughout each day for the entire year. The other assumption is that
the hot water demand is expected to average at 30 litres per person per day. The maximum
temperature of water achieved in the system is 60 degrees Celsius. The collector panes used in
this project are 2.1 square metres in area and the specific heat capacity of water is 1.16 kJ/KgK.
Method
Indirect solar water heating will be installed in the development to serve the Villa units in
line with the regulations. The hot water cylinder will be located in the yard or utility area and
will be served by thermal fluid pipes running in ducts from the solar collector panels located on
the roof.
Figure 6: Average irradiation for Lebanon (https://www.weather-atlas.com/en/lebanon-
climate)

Solar Water Heating Design 13
Figure7: Average irradiation for different cities in Lebanon (https://www.weather-
atlas.com/en/lebanon-climate)
Hot water demand calculation
𝑉 = 𝑎 × 𝑏 × 𝑐
Where,
V=Hot water demand per unit
a=Number of bedrooms per unit
b=Average occupancy per bedroom
c=average hot water demand per person per day
∴𝑉 = 6 × 30 = 180 𝑙𝑖𝑡𝑟𝑒𝑠, Available domestic hot water cylinder =200 litres Cylinder
Sizing for the number of collector panels
Q = Daily requirement for hot water × Specific heat capacity of water × Temp. diff.
Where
Q=quantity of energy required (Q) in kWh/day.
Specific heat capacity of water = 1.16 kJ/KgK
Temp. diff = 60 - 20 = 40℃ ℃ ℃
∴𝑄 = 200 𝑙𝑖𝑡𝑟𝑒𝑠 × 1.16 × 40=9280 kWh

Solar Water Heating Design 14
Estimating the size of the solar collector panel area (A) in metres
A= Number of days ×Q × Solar fraction
Solar irradiation × System efficiency
Where;
A= solar collector panel area
Number of days =365 days
Q=energy required in a day
Solar fraction=Amount of energy provided and the effectiveness of the collector relative to the
total amount of energy that the installation requires. A typical figure is 82%
Solar irradiation=1852kWh/m2 concidering not all seasons experience sunshine.
system average efficiency=60%
A= 365 ×9280 × 82
1852 ×60 ×1000
∴ A=2.49 m2
Collector panel area=2.1m2
Number of solar collector panels
= Total area
Collectorpanelarea=1.03 (Appx. 2 Collector panels)
Circulator Pump Capacity
Assumptions:
Total dynamic head-5metres
Number of bends and tees=5
Head loss per bend or tee=0.25m thus effective length =(5metres+(5metres*0.25)=6.25metres
Flow rate required = 2 Cu.m/hr

Solar Water Heating Design 15
Recommended circulator pump is Grundfos UPS 100 Series model 32-80 with variable speed,
0.245 Kw power consumption, maximum current of 1A as shown below.
Circulator pump (https://product-selection.grundfos.com)
Performance curve for the circulator pump (https://product-selection.grundfos.com)
Discussion
From the analysis, 9280 kWh per day is saved when using solar water heating. This
energy would be paid as electricity or fuel bill if no solar water heating was to be done in the
villa. This is quite some good savings for the Villa occupants and at the same time, they get o to
enjoy the hot water. Only one 200 litre-capacity hot water cylinder and 2 Nos. flat solar collector

Solar Water Heating Design 16
panels needed are needed to serve the villa occupants with hot water for an entire year. The
system efficiency is over 60% and this means that the villa occupants cut emissions of harmful
greenhouse gases by more than 60% which is acceptable.
Conclusion
In summary, solar water heating is an environment friendly method of heating water for
use at home compared to conventional methods such as use of fossil fuels. Solar water heating
comes with numerous advantages among them being that the water in the cylinder is kept hot
even for use at night when the sun is off. As a rule of thumb, only showers, bathtubs, and
washbasins should be supplied with solar-heated water for minimal wastage. Kitchen sinks, as
well as dhobi sinks, should not be supplied with solar-heated water.

Solar Water Heating Design 17
Reference List
Sharif, M.A., Al-Abidi, A.A., Mat, S., Sopian, K., Ruslan, M.H., Sulaiman, M.Y. and Rosli,
M.A.M., 2015. Review of the application of phase change material for heating and domestic hot
water systems. Renewable and Sustainable Energy Reviews, 42, pp.557-568.
Wang, Z., Yang, W., Qiu, F., Zhang, X. and Zhao, X., 2015. Solar water heating: From theory,
application, marketing, and research. Renewable and Sustainable Energy Reviews, 41, pp.68-84.

Solar Water Heating Design 18
Proposed Solar Water Heating Sketch
200
litres
capacity
In yard
2 Cu.m/hr at 6.5 m head
0.245kW
1A current
2 No. 2.1 m collector
panels on roof