Hey guys, I'm new to the forum here and am an engineer at a contractor that does alot of large commercial cooling / heating and power station work. However, I really dont know much about engineering for in home applications. So I wanted to ask a few questions and was hoping you guys could help me gain some understanding. (Moderators: if this is in the wrong forum, please feel free to move it to the correct forum)
Ok here are my questions:
- With ductwork for an AC system, what is the typical static pressure for the fans and would would be the expected pressure drop over the evaporator coil? Would this be any different for a system that is purely forced hot air vs cooling only? What about a combination system, would would be the best way to do this? I am familiar with the standard 20 deg F drop for air going over a cooling coil, but I never investigated the pressure side of the ductwork (I dont do much air flow where I work so I'm addmitedly weak in this area)
- If you have a system that does heating and cooling, what is the ideal way to distribute the air in the home (installation factors aside.) In many of the newer buildings the best way to go about air distribution is to use Under Floor Air Distributio, with the returns up high. This way you bring the warm air back to the cooling coil as the air seperates in the space. I would think this would work well for cooling but not for heating. For heating the return air should be closer to the floor. What is typically done in this regard and why?
- One thing we are seeing alot in the commercial side now is natural gas condensing exhaust gas water heaters. These are heaters where the return to the furnace is ducted into the exhaust stream and remains in the stream for a long enough time that the exhaust gas cools to below its dew point and starts condensing. These heaters are designed for this and have to have stainless steel breachings because the condensation of the exhaust gasses actually forms nitric acid. As such you also need to install an acid neutralization kit (which is essentially baking soda) to neutralize the PH of the exhaust gas. I have heard of high efficiency heaters that have a 95% AFUE, is this the same thing? If not what is different?
- In the commercial HVAC industry, most large chillers are water cooled using a cooling tower that allows cooling at the outdoor air wet bulb temp as opposed to the dry bulb temp. However, many people do make evaporative cooling units that use water sprayed on to a refrigerant coil to cool the air to lower than the dry bulb temperatures. I would like to know why this never caught on in the residential industry. I would think it would be pretty straightforward to design a unit that uses some domestic water to cool the condenser and saves electric consumption at the expense of purchasing water.
- I have heard that VFDs are making there way into the residential market. I assume that these are drives that will be utilized to run refrigerant compressors slower so that they are able to take advantage of cooler outdoor air temperatures when available. Is this correct? I am also familiar with VFDs being used on ductwork fans. I would imagine in teh residential market, the fans are to small to have any noticeable benefit from using a VFD but I wanted to see if that is the case.
Thanks in advance for any help.