Solar Hot Water Heater Design
Master’s Project Proposal
Robert P. Collins
Rensselaer Polytechnic Institute
9/18/13
Abstract
A household solar hot water heater is designed and optimized for use in Southeastern
Connecticut. An active, indirect solar hot water is chosen to obtain the efficiency and avoid the
working fluid freezing in the collector tubes in the moderate sunlight and varied Connecticut
climate. This design, coupled with a back up, electric hot water heater is shown to provide cost
effective hot water for the populous.
Introduction/Background
The amount of hot water used in the world is increasing as the middle class, and therefore the
average quality of life, increases. This, coupled with the rise in fossil fuel prices, creates a
growing need for a cheap, energy efficient, and environmentally friendly method for providing
household hot water. Household solar hot water heaters are a method of providing this cheap
and environmentally friendly hot water.
Problem Description
Solar hot water heaters are an obvious method for heating hot water in hot, sunny, and dry
climates, but are they a viable option for colder, less sunny environments? Connecticut’s
climate, which includes freezing winter conditions and an average daily sunlight of 4.5 – 5
kWh/m^2/day (Reference 1) necessitates a more optimized design to be effective. Solar hot
water heaters in this climate must either not be run in winter, or the working fluid exposed to the
atmosphere in the solar hot water heater collectors must have a freezing temperature below the
lowest possible temperature.
When and if the solar loop should be turned off will also be explored
Methodology/Approach
A solar hot water heater will be designed, using the bounds of the primary working fluid
encapsulated in the collectors, and its heat transfer to the secondary fluid, household water, with
a specified outlet temperature. The design will be down selected from the different types of solar
hot water heaters, which includes active and passive as well as direct and indirect types of solar
hot water heaters. Once down selected, the flow in the flow and heat transfer in the solar hot
water heater collectors will be modeled with the below methods:

The heat transfer between the sun and the water in the collector will be modeled using a
simple control volume. The sunlight and the cold primary fluid will be chosen as the
only inputs into the collector. Heat transfer out to the insulation to the atmosphere, the
reflected sunlight, and the hot primary fluid are the outputs. All other inputs and outputs
are assumed as negligible.
Reflected
Sunlight
Sunlight
Heat Transfer to
Atmosphere
Cold Primary Fluid
COLLECTOR
(CONTROL VOLUME)
Hot Primary Fluid
Figure 1: Collector Control Volume

The heat exchanger between the primary and secondary working fluids will be evaluated
using the epsilon-NTU method determine the maximum heat transfer between the two
working fluids.

Recorded on January 22, 1961 in Coventry, the lowest recorded temperature in
Southeastern Connecticut of -32°F, will be selected as the maximum freezing point
temperature for the primary working fluid.
Resources Required
The following information will be required:
 The monthly solar radiation for southeastern Connecticut
 A worst case efficiency of the heat exchange from solar to thermal energy
 An expected resistance of the flow in the pipe length
 Average household water usage
 Average household hot water temperature
Expected Outcomes
A solar hot water heater will be shown to be a cost effective method for heating household water
in Southeastern Connecticut. For the seasonal climate, an active flow, indirect solar hot water
heater is expected. The primary working fluid, which travels through the collector, will be
chosen to ensure that it is both food grade, in case there is contamination of the secondary loop,
and has a freezing temperature to avoid damage to the system in winter. A mixture of propylene
glycol and water is a commonly used fluid to heat and cool consumer products in the food and
beverage industry; this includes its use to cool boiling wort in the brewing process.
Milestone/Deadline List
1.- Functioning Web Portfolio and 100 word write-up with potential topic(s) - 9/9
2.- Tentative Project Proposal Draft - 9/16
3.- Project Proposal Draft - 9/23
4.- First Progress Report - 10/7
 Develop 5 sacred expectations – Requirements that the solar hot water heater must meet
to considered successful
 Select concept based on the 5 sacred expectations
 Determine relevant equations and evaluation tool
 Determine the primary working fluid that flows through the collector
5.- Second Progress Report - 10/28
 First iteration of the design and evaluation of results that satisfies sacred expectations
 Size heat exchanger
 Choose insulation of collector
 Determine the efficiency of the heat exchanger for the operating conditions
 Evaluate if there are any conditions where the solar hot water system should be turned
off.
6.- Final Draft - 11/11
 Re-evaluate results, optimizing the design.
 Update Abstract and Conclusion to reflect results
 All figures
 Finalize references and citations
7.- Preliminary Final Report - 11/25
 Revise based on comments
 Final proofread
8.- Final Report - 12/13.
 Revise based on comments
References
http://energy.gov/energysaver/articles/solar-water-heaters
Varied source with lots of general information on types of solar hot water heaters; useful as a
general source
http://www.fsec.ucf.edu/en/consumer/solar_hot_water/index.htm
Some useful information on the different applications of solar hot water heaters
http://www.asse-plumbing.org/chapters/NOH%20SolarWtrHtg%20Pres.pdf
Good description of hot water heater setup, angle of orientation, etc.
http://www.nrel.gov/docs/legosti/fy96/17459.pdf
General consumer information on choosing the right solar hot water heater
http://www.renewableenergyworld.com/rea/blog/post/2013/03/how-solar-pv-is-winning-over-csp
PV vs. Concentrated Solar Power – PV winning.
http://www.nrel.gov/gis/solar.html
Solar energy maps
http://www.metrosolinc.com/pdf/SolarDHW.pdf
Active vs. passive solar hot water heaters
http://www.netstate.com/states/geography/ct_geography.htm
Lowest temperature in Connecticut
Young, Robert C. “The Perceived Performance of a Solar Flat Plate Collector Domestic Hot
Water Heating System” March, 2011.