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The provided [[#spreadsheet]] gives heating and air conditioning requirements in BTU/h (British Thermal Units/hour).
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= HVAC Integrated Design =
This article works through the considerations in designing heating, ventilation and air-conditioning (HVAC) systems for year-round living on a 50-foot boat. Some of the concepts and calculations can also be applied to your next house.
The design is not optimal. When the furnace fails in the coldest weather there is a heating shortfall of 21,560 BTU or 6 kilowatts (kW).
=== Description ===
The HVAC system uses a blend of loosely coupled systems to provide maximum energy efficiency and redundancy for a year-round live-aboard. Fresh-air ventilation uses small zone-based air vents but this makes humidity control difficult. The heating and cooling systems use a shared circulating-water distribution system to minimise bulkhead pass-throughs. Heating is by a diesel furnace with backup from a diesel fireplace. Cooling is by a chiller with keel cooler, with backup from the cold-plate refrigeration system. Hot water is heated by the engine, the diesel oven, a [https://en.wikipedia.org/wiki/Solar_thermal_collector solar collector ] or AC elements using shore power or the house bank.
[[File:blendedHVAC.png|thumb|400px|left|The heating, ventilation and air-conditioning are a blend of loosely coupled systems to provide maximum energy efficiency and redundancy]]
Hot water is heated in several ways. In port in summer, the water is heated by standard electrical elements operating off the alternating current (AC) system. In winter, it is heated by the water jacket on the diesel oven. If the oven is not in use, and there is no other source of heat, the hot water tank defaults to the electrical elements.
Use an anti-scald, balanced-pressure shower valve (not a tempering valve!) on the showers to regulate the water to 120 Fahrenheit (F°F) 48.8 Celsius (C°C). This will avoid scalding people, and reduce water consumption. Bathers will be able to mix the water faster to a comfortable temperature.
=== Refrigeration ===
== Control Zones ==
For heating, ventilation and air-conditioning distribution and control purposes, the boat is divided into the zones in the below table. With a K=1(see [[HeatingCalculation|Heating Calculation)]], the boat requires approx. 37,810 BTU/h of heating. The main diesel furnace supplies this, sufficient for the coldest weather.
<table width="80%" border="1">
</table>
But what happens in an emergency? In the event the furnace fails, the Bristol Pacific model diesel stove in the galley can provide 6,500-16,250 BTU to heat the forward accommodation. At the lower heat setting it could maintain a temperature differential of 21 C°C, while the higher one maintains the design differential requirement of 55 C °C in the forward compartment.
At the lower setting, water pipes, etc., are protected down to -20 C°C, a not infrequent winter temperature, which is why the design requirement is the higher 55 C °C differential. Because the galley stove alone cannot heat the whole boat in the event of a furnace failure, additional heat has to be supplied by the diesel fireplace in the salon. A fireplace such as the Bubble produces only 3.5 kW (11,946 BTU), good for a 17 C °C differential overall. So it will only heat the pilothouse and salon, not the aft cabin.
Therefore in an emergency in the coldest weather we have a heating shortfall of 21,560 BTU (6 kW). This is not critical above deck in the salon and pilothouse, since there are no water pipes there. But it is critical in the aft head.
[[HeatingCalculation|Calculating Heating Requirements]]
[[VentilationCalculation|Calculating Ventilation Requirements]]
[[AirConditioningCalculation|Calculating Air Conditioning Requirements]]