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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:

== Heating ==Methods of calculating requirements for both heating and air conditioning tend In addition, to provide backup in the arcane case of failure in a severe cold spell, a diesel bulkhead fireplace in the salon, such as the Kabola <ref>http://www.kabola.nl/</ref> Old English Diesel Room Heater or the very simplisticHarworth Bubble <ref>http://www. There are too many variables to consider, ebubbleproducts.gco., uk/</ref> is also plumbed into the colour distribution system. Other types of the deck paint affects the amount of heat gain insidebulkhead heater are available from Dickinson Marine <ref>http://dickinsonmarine. The author has developed a spreadsheet application that tries to strike a balance between simplicity com/</ref>, Refleks <ref>http://www.refleks-olieovne.dk/</ref> and accuracySigmar <ref>http://www. When calculating heating requirementssigmarine.com/</ref>.Initially a fireplace was desired for lifestyle reasons, but as the design evolved it ignores heat gain through southern exposure windows became a backup system. The Dickinson Bristol Diesel Cook Stove in the daytime and heat loss through all windows at night. It galley can also ignores sporadic heat gain from equipment and appliancesthe forward accommodation, but it is not part of the main distribution system.

V = volume of the accommodation in cubic metres== Engine Cooling ===

T = Under way, engine coolant circulates through the hot water tank, and hence to a water-water heat exchanger with keel cooler. Another feature of this design is that raw seawater is not circulated through the engine. There is a bypass circuit around the water heater that closes thermostatically when the heater is at temperature differential in degrees Celsius.

K = dispersion coefficient (how heat ‘lossy’ is your 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 in the engine room provides engine cooling.

B = 4 == Hot Water ===Hot water is heated in several ways. In port in summer, the water is heated by standard electrical elements operating off the alternating current (conversion factor to BTUAC)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.

To calculate the VolumeUse an anti-scald, for each living space multiply Length * Width * Height in feet as shown in balanced-pressure shower valve (not a tempering valve!) on the below table. Use judgement in deciding whether showers to list each space individually or as part of a sectionregulate the water to 120 Fahrenheit (°F) 48.8 Celsius (°C). The calculator This will do avoid scalding people, and reduce water consumption. Bathers will be able to mix the conversion water faster to metrica comfortable temperature.

C = Additional cooling for one zone is provided by a cold-plate refrigeration system. A high-efficiency cold-plate design for the refrigeration will reduce AC loads, while not imposing a continuous direct current (F – 32DC) * 5/9load. Excess capacity may be used for air conditioning.

K = 3.0 - 4.0 (Simple construction, simple windows - Not insulated)= HVAC Scenarios ==

K = 2.0 - 2.9 (Simple constructionWith this integrated design, simple windows - Poorly insulated)the following scenarios apply:

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 Main engine in heads and the galley to remove airborne odours before they spread through the boat. From a ventilation viewpoint, the most effective method is an integrated HVAC 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 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 air.use:

Excess humidity causes condensation on windows and Central hot water pipes. It can blister paint, rust metal and warp wood, and cause electrical faults. Dust mites, fungus, mildew and mould thrive in humid conditions, aggravating allergies and sometimes damaging lungs. Insects like clothes moths, cockroaches and fleas also like high humidity.AC is turned off

Unfortunately I decided against an air distribution system in favour of a water system for heating Fireplace and air cooling. This was to minimise the scope of pass-throughs in water-tight bulkheads but like many design decisions this had further consequences. It made an integrated ventilation/humidification system impossible.oven provide central and space heat

The alternative to running fairly large air vents the length of the boat is local ventilation in the main zones of the boat. This is far from ideal. In both summer Central furnace and winter the air intakes will be working against the air conditioning and heating systems, respectively, and deck-mounted dorades for intake and return air are multiple hull openings. The ventilation distribution system must be designed carefully to minimise these risks of water entering.fail:

Humidity control is also difficult with local ventilation; although it may be possible to incorporate small electronic dehumidifiers into the vents. Electronic dehumidifiers use small peltier heat pumps but consume a fair bit of electrical energy. For small vents, mechanical dehumidifiers don’t scale down, Fireplace and desiccated dehumidifiers are overly complex.oven provide space heat

== Air Conditioning == Oven provides hot waterA water DC-based chiller AC inverter provides air conditioning. The chiller circulates chilled electricity to hot 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.)elements

Additional cooling for one zone For heating, ventilation and air-conditioning distribution and control purposes, the boat is provided by divided into the Glacier Bay cold-plate refrigeration system [8]zones in the below table. With a K=1 (A high-efficiency 12-VDC old-plate design was chosen for see [[HeatingCalculation|Heating Calculation)]], the refrigeration to reduce AC loadsboat requires approx. 37, while not imposing a continuous DC load810 BTU/h of heating. Excess capacity may be used The main diesel furnace supplies this, sufficient for air conditioningthe coldest weather.)

Cubic feet per minute (CFM) or litres per second (L<tr><th colspan="5">HVAC Zones</s) of outside air brought into the boat CFM per person: CFMth></p CFM per unit floor area: CFM/ft2 Air changes per hour (ACH)tr>

Standards for ventilation differ, and have varied over time subject to lobbying, energy efficiency doctrines and the emergence of sick building syndrome. A reasonable yardstick is somewhere in the range of 0.5-<tr> <th>Description</th> <th>Zone</th> <th>Distribution</th> <th>Air<br> Conditioning<br>BTU (K=1.25 ACH or, more precisely, )</th> <th>Heating<br>BTU (K=1.0 ACH translating to around 1.66 CFM per 100 cubic feet of cabin volume. You can double check this to ensure at least 15 CFM)</th></p.tr>

For example<tr> <td>Forward cabin</td> <td>1</td> <td>44% </td> <td>24, assume a boat having 6349</td ><td>16,000 cubic feet of volume and berths for five people. Using 1.0 ACH this yields 99.6 CFM and 15 CFM637</td></p yields 75 CFM.tr>

Maximum air velocity in ventilation ducts and vents should not exceed <tr> <td>Aft cabin</td> <td>2.6-3.3 ft</s (0.8-1.0 mtd> <td>17%</s) to minimise noise and differentials in air pressure. Air ducts for combustion systems can run as high as 40-66 fttd> <td>9,408</td> <td>6,428</s (12-20 mtd></s).tr>

Let’s work a complete example<tr> <td>Pilothouse</td> <td>3</td> <td>18%</td> <td>9. Assume a salon of 1280 cubic feet. At 1.0 ACH this requires 21.3 CFM:961</td> <td>6,806</td></tr>

CFM = Volume * ACH<tr><td>Salon</60 minutestd> <td>4</td> <td>21%</td> <td>11,621</td> <td>7,940</td></tr>

The corresponding vent area with a velocity of 2 ft<tr> <td>Engine room</s is:td> <td>5</td> <td>-</td> <td>-</td> <td>?</td></tr></table>

Vent Area = CFM/(Velocity * 60 seconds)= 21.3/120= 0.18 sq ft= 25.But what happens in an emergency? In the event the furnace fails, the Bristol Pacific model diesel stove in the galley can provide 6 sq ,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 inthe forward compartment.

Close enoughAt 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.

In this case, Therefore in an emergency in the coldest weather we could put have a 5- x 5-in intake vent at one end heating shortfall of 21,560 BTU (6 kW). This is not critical above deck in the salon and a vent of the same size at pilothouse, since there are no water pipes there. But it is critical in the other end with an exhaust fan driving 2 ft/saft head.

==Related Pages = Hot Water ===Hot water is heated in several ways. In port in summer, 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.

=== Engine Cooling === === Refrigeration === == [[Category:HVAC Scenarios ==]]