Entries Tagged 'HVAC' ↓

This is a challenge if I have ever run into one. We have done this quite a few times at this point and each new job offers challenges and requires specific attention that others have not. The 1st problem with a hybrid hot-water system (hybrid meaning it uses both radiators and underfloor tubing) is the temperature variance in the two conducting units. The radiators we work with are generally cast-iron as these are in the older historic homes, and those radiators operate at a supply-water temp of 160-180 degrees, the radiant flooring systems operate at 120-140 degrees. As we often are working with an existing boiler (and even with new boilers), the boiler has one input and one output for heating water. Therefore we are obligated to keep the boiler operating at the higher temp – usually we settle at 175 degrees Fahrenheit. This then requires us to use “circuits” for each type of heat conductor and “circulators” to move the water. Generally in a historic home, the radiators are on one circuit and the radiant flooring is on another. With those two circuits, we use three circulating pumps or circulators to move the water through the system. The first circulator is the boiler circulator and that is mounted on the return pipe just above the boiler, the second circulator is on the supply side of the main hydronic loop (I will define that loop in another post) which is basically to say it is on the supply pipe for both circuits, the third circulator is on the return end of the in-floor heat system right after the manifold (check the post for in floor heating) for the floor heat. Got all that? That will take me into the next post, the main hydronic loop.

This evening, I received a concerned email from a client regarding the return-air portion of the HVAC system we installed in one of his properties. The traditional method for installing return air in older homes (and in most new ones) is to use joist and stud spaces as the duct and panning the joists/studs in the unfinished spaces. We do seal these chases from insulation/attic air/basement air/ and outside air. The client contends that this seems insufficient and would prefer to have the whole duct done in metal. I have always shyed away from this option as metal attracts condensation and that is a pathway to mold problems when encased in drywall and wood. Provided the chase is adequately sealed (subfloor glued, drywall taped, insulation separated, etc) I cannot see any cost-benefit to a more complex system. It adds cost and won’t truly be any more air-tight unless the joints are covered with tape or mastic. Plus the moisture issue comes back into play. We have tinned return air before but that was generally in larger systems where we were drawing return air from multiple locations and thereby justified the additional cost.

Actually, I have always thought we went above the level of the other builders in the area as we do the calculations and provide at least one return per floor – often we provide two per floor. Sometimes this is easy as we are doing multiple systems but we also do this in single-system situations as well. Other builders I have seen simply put a single return (they call it a “cold-air-return”) on the first floor. Of course thermodynamics tells us the total lack of efficiency this provides- a frosty first floor in the winter as all the cold air heads its way, and a steamy 2nd and/or 3rd floor as the cold air being pumped from the vents only goes as high in the room as the vent is on the wall. I have often called this the “Hot-Air-Balloon-Effect” as all the hot air gets trapped in the upper six feet of the higher floor. Meanwhile the cool conditioned air on the upper floors is leaving the vents (what little actually can be force-fired against its will) and immediately dropping to the floor as it begins its natural decent to the “Cold-Air-Return”. Truly this is a vicious cycle if I have ever seen one.

Of course in a perfect world where everyone has unlimited funding and projects are executed with no budgetary restraints we would have separate send and return air pipes to each room and zone of the house. These zones would all be balanced using individual electronic zone dampening systems attached to individual programmable thermostats in each room so a level of comfort and efficiency could be reached that has never before been achieved in historical restoration. However, it would also be somewhat idiotic to spend any of this money had you not also addressed the problems these old houses have with efficiency in other areas. You must make the building “envelope” as air tight as possible so the conditioned air is not just leaving the house. Also, you would need to achieve the proper insulation values for your homes climate region. (It should be noted at this time that the current Energy Star requirements for such a rating in Saint Louis are R-49 for the attic/crawlspace). For those of you whom cannot convert this rating into thickness in blown-in-loose-fill-cellulose, this would be about 14″ thick. If you do not have this rating of insulation, plus the correct ratings in the other exterior walls of your home, plus the correct insulation in your basement/crawlspace, plus a proper vapor-barrier, and plus a properly sealed building envelope, you would be asking the impossible of an HVAC installer to correct the problem with a space-age duct system. Your furnace would end up in a conundrum akin to trying to fill a cup with water when the cup has holes in the bottom and sides.

This topic deserves more attention, but I am done for the moment. I welcome comments.