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The heating, ventilation and air-conditioning systems are a blend of loosely coupled systems to provide maximum energy efficiency and redundancy. This example 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).

A basic heating, ventilation and air conditioning system is described below. In this case the The design goal is a year-round live-aboard in north-eastern North America. For completeness in understanding the trade-offs made, the engine cooling system, hot water and refrigeration and watermaker are also shown. Some of the design considerations are:

The requirement for a single fuel type effectively eliminates propane heating in favour of diesel. Diesel is anyway much safer. It is also more efficient, providing around 140,000 BTU (British Thermal Units) per gallon(gal), compared to 91,000 for propane.

The first major issue is whether to use forced air or circulating water to distribute heating and cooling. In the beginning, memories Memories of cold radiators in grade school in the dead of a Canadian winter, and the comfort of humidity control with forced air in modern homes predisposed me the solution to forced air. Over time, I the solution changed my mind several times. In the end, circulating water was chosen to:

== Ventilation == Towel Rails ====

Fresh air ventilation is required to replenish oxygen removed by people and sources of combustion, and to dilute odours and pollutants. Local exhaust ventilation is required in heads and the galley to remove airborne odours before they spread The main distribution system also routes through the boattowel rails in various compartments. From a ventilation viewpoint, These are switched out of the most effective method is an integrated HVAC circulating water system with air distribution and local controls in each cabin. Such a system can include an air-to-air heat exchanger to precondition the temperature of the air summer and recover energy, and a humidifier/dehumidifier to control levels of indoor moisture. Humidity control is especially important in hot humid climates where unconditioned ventilation can deliver 1-lb of water per cubic foot of intake airheated with AC elements.

Unfortunately I decided against an air distribution system in favour of a Under way, engine coolant circulates through the hot water system for heating tank, and air cooling. This was hence to minimise the scope of pass-throughs in a water-tight bulkheads but like many design decisions water heat exchanger with keel cooler. Another feature of this had further consequencesdesign is that raw seawater is not circulated through the engine. It made an integrated ventilation/humidification system impossibleThere is a bypass circuit around the water heater that closes thermostatically when the heater is at temperature.

The alternative to running fairly large air vents the length of In winter if the boat is local ventilation in the main zones out of the boat. This is far from ideal. In both summer and winter water, the air intakes will engine may have to be working against run to charge the air conditioning and heating systemsbatteries. In this case, respectively, and deckan optional water-mounted dorades for intake and return air are multiple hull openings. The ventilation system must be designed carefully to minimise these risks of water enteringradiator in the engine room provides engine cooling.

Humidity control === Hot Water ===Hot water is also difficult with local ventilation; although 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 may be possible to incorporate small electronic dehumidifiers into is heated by the ventswater jacket on the diesel oven. Electronic dehumidifiers If the oven is not in use small peltier heat pumps but consume a fair bit of electrical energy. For small vents, mechanical dehumidifiers don’t scale down, and desiccated dehumidifiers are overly complexthere is no other source of heat, the hot water tank defaults to the electrical elements.

If you plan to spend your time in hot humid climatesUse an anti-scald, you should consider balanced-pressure shower valve (not a solution that incorporates tempering valve!) on the showers to regulate the water to 120 Fahrenheit (°F) 48.8 Celsius (°C). This will avoid scalding people, and reduce water consumption. Bathers will be able to mix the water faster to a dehumidifiercomfortable temperature.

== Air Conditioning = Refrigeration ===A water-based chiller provides air conditioning. The chiller circulates chilled water through a water distribution system to the cabins, to cool them in summer. All pipes should be insulated to prevent condensation. (Similarly, if you opt for forced air, the ducts should be insulated.)

The heat exchanger can be water-air or waterAdditional cooling for one zone is provided by a cold-waterplate refrigeration system. A waterhigh-air exchanger would have to work against efficiency cold-plate design for the heat in the engine roomrefrigeration will reduce AC loads, so it makes more sense to use while not imposing a water-water heat exchanger with a keel cooler as a heat sink. This is overall more efficient continuous direct current (the temperature differential is higher with waterDC), and avoids generating extra heat in the engine roomload. Excess capacity may be used for air conditioning.

Additional cooling for one zone is provided by the Glacier Bay === Watermaker ===For cold-plate refrigeration system [8]. (A high-efficiency 12-VDC old-plate design was chosen for water expeditions, the refrigeration water intake to reduce AC loads, while not imposing a continuous DC load. Excess capacity may the watermaker should be used for air conditioningpreheated.)

== Related Systems HVAC Scenarios ==

=== Hot Water ===Hot water is heated in several ways. In port in summerWith this integrated design, the water is heated by standard electrical elements operating off the AC. 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.following scenarios apply:

In winter if the boat is out of the water, the engine may have to be run to charge the batteries. In this case, an optional water-air radiator Oven in the engine room provides engine cooling.use:

Use an anti-scald, balanced-pressure shower valve (not a tempering valve!) on the showers to regulate the Central furnace is turned down Central hot water to 120 F. This will avoid scalding people, and reduce water consumption. Bathers will be able to mix the water faster to a comfortable temperature.AC is turned off

Fireplace and oven provide central and space heat Central furnace and distribution system fail:  Fireplace and oven provide space heat Shore AC power fails:  Oven provides hot water DC-AC inverter provides electricity to hot water elements == 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"> <tr><th colspan="5">HVAC Scenarios Zones</th></tr> <tr> <th>Description</th> <th>Zone</th> <th>Distribution</th> <th>Air<br> Conditioning<br>BTU (K=1)</th> <th>Heating<br>BTU (K=1)</th></tr> <tr> <td>Forward cabin</td> <td>1</td> <td>44% </td> <td>24,349</td ><td>16,637</td></tr> <tr> <td>Aft cabin</td> <td>2</td> <td>17%</td> <td>9,408</td> <td>6,428</td></tr> <tr> <td>Pilothouse</td> <td>3</td> <td>18%</td> <td>9.961</td> <td>6,806</td></tr> <tr><td>Salon</td> <td>4</td> <td>21%</td> <td>11,621</td> <td>7,940</td></tr> <tr> <td>Engine room</td> <td>5</td> <td>-</td> <td>-</td> <td>?</td></tr></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, while the higher one maintains the design differential requirement of 55 °C in the forward compartment. At the lower setting, water pipes, etc., are protected down to -20 °C, a not infrequent winter temperature, which is why the design requirement is the higher 55 °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 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. Finally, some heating has to be provided to the engine room to keep water tanks and pipes from freezing. Obviously some further development is required in the design of the back-up heating. Increasing the output of the diesel stove is not a good option, as this would tend to make it less useful as a cook stove. Perhaps the Bubble should be re-located to the aft cabin, but this negates its lifestyle purpose. More practical solutions are to shut off the water to the aft head and run the engine to keep the engine room warm. Another solution is to have an aft engineroom and a contiguous forward accommodation space. == Related Pages == [[HeatingCalculation|Calculating Heating Requirements]] [[VentilationCalculation|Calculating Ventilation Requirements]] [[AirConditioningCalculation|Calculating Air Conditioning Requirements]] == References ==  [[Category:HVAC]]