Matthew Harwell
Project Summary
The purpose of this project is to evaluate the heat loss paths from a pool of water
and to assess how well a pool cover precludes heat transfer via these methods.
Furthermore, different mechanisms of heating a pool will be evaluated including solar
energy and resistance heaters.
The heat loss paths to be analyzed include convection from wind, night radiation
to the atmosphere, and evaporative cooling from dry air. The heat losses will first be
evaluated without a pool cover, then these heat lost paths will be evaluated with a pool
cover.
Night radiative losses have been known to freeze leaves on cool clear nights. Its
role will be examined in cooling a pool at night. The atmosphere’s temperature ranges
from 230 K on a cold clear sky, to 285 K in warm cloudy conditions. The radiative heat
flux will be examined between these temperatures.
The pairing of convection and evaporative cooling plays an important role in daily
life. Every time we sweat while running, these two heat transfer mechanisms occur. In
desert conditions, people have discovered by putting a pool on their roof, their homes will
stay cooler especially if they have a fan blow across the pool. In areas where water is
cheap and plentiful but the power supply may be inadequate or expensive, it has been
demonstrated that this system can reduce home temperatures during peak day
temperatures by up to 6C. Evaporative cooling has been used to cool cow barns to
relieve thermal stresses felt by the cows. Convection and evaporative cooling occur
simultaneously but their magnitudes are independent. Convection is driven by a
temperature gradient and evaporative cooling is driven by a density gradient, controlled
by the relative humidity of the air.
A constant 70F pool will be assumed as the initial condition, and environmental
conditions will be varied to study how the magnitude of heat conduction out of the pool
will be affected in each situation. Ultimately, this should lead to a better understanding of
pool thermodynamics and allow a pool owner to react appropriately to different
environmental conditions. A common way owners counter heat loss from their pool is to
cover it with a pool cover. Pool covers have been marketed to the public to minimize the
amount of heat loss from a pool. A pool covers ability to restrict the heat loss from a pool
will be evaluated.
After understanding the heat loss mechanisms, different means of providing heat
to a pool will be analyzed. A thermosyphon solar water heater and a pumped active solar
water heater with flat plate collector will be analyzed to determine how effective these
methods are in heating a pool. The cost and efficiencies will be compared to that of a
commercial pool heater.