COIL PARALLEL WITH EXISTING HOT WATER HEATER
ADDITIONAL INFORMATION:
Each gallon of water circulated through the system delivers a definite quantity
of heat which is dependent on the water temperature drop for which the system is
designed. Water temperature drop is the difference between the temperatures of the
water leaving the furnace and the water returning to the furnace.
It will be noted that the smaller water temperature drops result in less BTU/H
capacity per GPM. This means an increase in the GPM requirements of the pump. It
has been found that a 20-degree water temperature drop usually provides the most
economical selection of pump and pipe sizes.
It should be noted that under actual operating conditions the temperature drop
usually is considerably less than that for which the system is designed and will not
appreciably affect the outputs of the heat distributing units. The temperature drop
provides a starting point for determining the number of BTU/H which will be
delivered to the heat distributing units by the circulation of each gallon of water per
minute.
In accordance with the definition of a BTU, if one pound of water drops one
degree Fahrenheit as it circulates through the forced hot water heating system, then
one BTU is given off. A gallon of water, weighing approximately 8.3 lbs. At the
temperatures used in a system, will give off 8.3 BTU if it drops one degree as it is
circulated through the system. One gallon per minute for 60 minutes, or one hour,
will, if it drops one degree, give off 8.3 x 60 = 498 BTU/H.
