544
edits
Changes
m
→Heating
Methods of calculating requirements for both heating and air conditioning tend to the arcane or the very simplistic. There are too many variables to consider, e.g., the colour of the deck paint affects the amount of heat gain inside. The author has developed a spreadsheet application that tries to strike a balance between simplicity and accuracy. When calculating heating requirements, it ignores heat gain through southern exposure windows in the daytime and heat loss through all windows at night. It also ignores sporadic heat gain from equipment and appliances.
The spreadsheet uses the following formula to determine heating requirements in British Thermal Units per hour (BTU/h) [1]:
<pre>BTU = V * T * K * B</pre>
K = 0.6 - 0.9 (Advanced construction, triple pane windows - Well insulated)</pre>
With K=3, the calculator yields 19 BTU/ft-sq while experts recommend 20 BTU/ft-sq, so we have good agreement at one end of the range. How aggressive you should get towards the other end is impossible to say. However, with the three heating systems specified for the boat there should be ample scope for increasing or decreasing the heat without upsetting the balance of the system. In a system that is under-sized, the furnace will run for long periods. In an over-sized system, the furnace will cycle frequently and run for very short periods. Typical furnaces are 80-90% efficient, so if you need 100,000 BTU output you will need one rated at, say, 125,000. In general, a heating system should be sized 154% of the requirement(192,500 in this example), so it runs at about 65% duty cycle.
== Ventilation ==