Posts Tagged ‘Mechanicals’

Retrofit HVAC Recommendations That Won’t Break The Bank

Nov 23, 2007 |  by  |  Craftsman Archives  |  Share

If you remember, a couple months ago my neighborly engineer whipped up the first part of a three part series discussing heating and cooling recommendations for older homes. The idea was to provide quality info for folks at all levels of the socioeconomic spectrum. From the rich financially gifted to the poor financially challenged. And now after two long months, part two is here. I’m sure you all have been waiting with unfettered anticipation…I know I have.

So here ya go.

My middle-of-the-road recommendation consists of two parts:

mini duct floor outlets Retrofit HVAC Recommendations That Wont Break The Bank#1: Mini duct system – “An air distribution system based on a principle known as aspiration, where the air is injected into the room at a much higher velocity (i.e. 1600 – 2000 ft./min.) than with conventional air conditioning systems (i.e. 300 – 400 ft./min.). As a result, the system provides complete air circulation throughout the space, eliminating the typical 2-3 degree temperature stratification between the floor and ceiling.”

Since the radiant heating AND a mini duct system together would be too expensive to classify as middle-of-the-road, the mini duct system would work well by itself in my neighbor’s home. We have already established that the existing duct work is leaky and is large enough to accommodate the mini duct system inside it. The air handling unit (AHU) that will be necessary for the mini duct system could be located in the attic or in the basement. In this climate (midwest temperatures) if the AHU is to be located in the attic, an AHU with a heat pump would be a good choice versus an AHU with a hot water coil which might freeze if the system were to fail in the winter.

A hot water coil and a boiler is, however, the more efficient option and would work well if the AHU were located in the basement. With the right equipment selection and application a hot water coil system is more efficient at heating than a heat pump system. The hot water for this system could be generated by either a boiler or a combination domestic water heater and boiler. The combo option would kill two birds with one stone if one was inclined to replace the water heater in the near future anyway. Either choice will likely require a buffer tank to eliminate the chance that the boiler will “short cycle”, or turn on and then off in 5 minutes or less. Short cycling needs to be avoided, as it significantly shortens the life of a boiler.

Another option, if cost is a concern, is to use an electric heating coil in the AHU.

#2: Humidifier

A humidifier is still a good idea with this system, especially because of the “leaky” construction of the house. In the winter, all the drafts that infiltrate through the windows and doors consist of very dry air. To combat that dryness, a whole house humidifier integrated into the AHU should work nicely.

The middle of the road recommendation does not include an insulation retrofit, and therefore an ERV (energy recovery ventilator) will not be necessary either. My neighbor’s “leaky” house, without much of an air or moisture barrier built into the walls [craftsman note: the walls in a couple of the rooms upstairs are pretty cold during the winter months. Makes you want to position the bed in the middle of the room, like a residential island or something], actually results in the desirable effect of ventilating the home. Of course, this is not ideal because it makes the house feel drafty and colder than the thermostat would indicate. Nonetheless, the ventilation needs are met.

Of course, what I want to know is approximately what a retrofit as well as a new installation in a 2000 sq. ft. home would cost. My engineer friend wasn’t willing to venture a guess, so I guess until I’m ready to get an estimate I’ll just have to sit and wonder what the cost of high speed air might be.