H V A C S y s t e m D e s i g n
In a forced air system, conditioned air should enter the room slowly. A good design picks a happy medium between the quiet of slow moving air and the required volume of air movement for the temperature and ventilation requirements of the room.
In a low air speed HVAC system, cooling ducts can be placed in the ceiling or high on the walls so the the heavy cool air drifts down over the space naturally. And of course heating ducts on the floor or low on the walls will let warm light air drift up into the room. These duct placements eliminate the need for rushing air to be forced against the natural convection currents in the room.
To slow the air just before it enters the room, we can specify still air boxes in which rapidly entering air is dispersed and distributed more slowly through a number of ducts. A still air box can also help reduce noise transmission both in and out of the room.
If you are custom building a room, we may recommend that you consider radiant floor heating; it's very comfortable and quite quiet. Because the surface area of the floor is so large, a very low floor temperature such as 81 degrees Fahrenheit will evenly heat the room. In winter, radiant heat does not contribute to low humidity as does forced hot air. Also, because radiant heat eliminates the need for radiators and ducts, the acoustic layout of the room and optimal system setup need not consider these obstacles.
Radiant floor heating may actually reduce energy costs too. Some of the heat radiated by the floor directly warms you without warming the air in the room first, thus reducing your body's heat loss. Therefore you may feel warm in the room even though the actual air temperature may be cooler.
There are a couple of disadvantages to radiant heat. When you return from an extended vacation, the radiant heating system will need more time to warm the room because of the larger thermal mass involved. Also, care must be taken during construction and any subsequent renovations to protect the heating tubes in the floor from being punctured. And it is very important to get a good HVAC contractor with experience and a good track record with radiant heat to get a properly engineered installation if you decide to go this route.
You may also wish to consider radiant cooling, particularly if you live in a dry climate. When a conventional air conditioning system cools hot, moist air, the excess water condenses and drips into a drain. While there will be some dehumidifying with radiant cooling, you can hit what is considered the dew point while lowering the temperature and not dehumidify the air. So with radiant cooling, the moisture will remain in the air. However in humid environments it is possible that it might leave the room feeling somewhat clammy. In dry climates this isn't a problem because the air contain no excess of moisture.
If you are considering a radiant system, we strongly suggest that you contact an experienced HVAC contractor and visit one of their installations to see how you like it.
If you would like to control humidity and temperature of a room, then you need a dehumidification unit with air conditioning capabilities. A properly engineered installation will hold temperature within +/- 1.5 degrees and humidity within 2% at a cost of never shutting the unit off. Because the compressor is always on, the operating costs are substantially higher. And for a state-of-the-art system, it is actually possible to hold temperature to within 3/10 of a degree Farenheit and 1% humidity.
Each HVAC project is different. Lifestyle considerations, performance issues, budget, and personal preferences mandate a customized approach to each individual job.