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High Efficiency Homes – Avoid Trouble Ahead

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Behold, the home of the future!  The home with special high-efficiency windows, doors, appliances, and lights.  A space-age ventilation system that exhausts harmful pollutants and brings in healthy clean air for the family, pets, and plants; so they all flourish in this virile environment.  The home’s space-age construction, nearly airtight and well insulated, ensures that it is effortless to heat and cool.  The home’s integrated control system works seamlessly (and best of all, the whole house functions on a small steady stream of power produced on-site.  Won’t it be great to live in the house of tomorrow?  

But wait, these homes are available… now!   

  • Increased code requirements mandate tighter envelopes, better windows, and more insulation.  
  • High efficiency appliances are not for the rich or a radical environmentalist, they are standard fare at the local department store.   
  • Bright colorful LED lights and integrated control systems are inexpensive, easy to find, and easy to install.  
  • Ventilation systems are required by code because homes aren’t drafty, leaky sieves anymore.    

This technological marvel is built every day, but some of these houses are as comfortable as a cave, and not a capsule.  Why?  HVAC contractors MUST follow good design practices, or their customers will suffer because of three big challenges.     

Challenge 1: Comfort 

In tight homes, ventilation air is needed to dilute volatile organic compounds, cooking odors, and other household smells.  The strategy employed to bring in oxygen-rich outdoor air must be carefully considered.  Winter outdoor air is cold and dry; in the summer it is hot and humid.  Raw ventilation air needs to be mixed with conditioned air or it will create real discomfort.  Further, humid summer air must be effectively pretreated, or the added moisture will directly reduce the occupant’s comfort.   

Challenge 2: Humidity 

High efficiency homes have moisture problems, even in dry climates.  Occupants create humidity when they cook, bathe, and clean. In addition, moisture is made when they perspire or breathe, and the same is true for family pets and house plants. Additionally, ventilation air in many climates pumps more humidity into the house all summer long. To compound the issue, tight homes also retain moisture and traps it inside. This leads to homeowner discomfort and building decay. Sheetrock begins to grow black fuzzy organic material, wood floors crown, and odors from the dampness contributes to an already miserable situation. A properly sized cooling system is the first right step. However, moisture loads can be more than the air conditioner can handle.

Challenge 3Low Airflow 

Before: In old, leaky, under-insulated homes, any given room needed a lot of conditioned air to maintain comfort.  When the HVAC system came on, a large volume of conditioned air rushed into the room.  The warmed, or cooled, air swirled and mixed with the room air; the turbulence moved the conditioned air throughout the space.   

Now: In today’s energy efficient homes, rooms usually have a minuscule load and it only needs a wisp of air.  Small loads and low airflow should be a good thing, right?  The impact is that the wisp of air provides no turbulent force to mix with the room air, so cool air puddles on the floor, or warm air floats up to the ceiling.  The warm or chilled air will eventually dissipate (after all nature hates a vacuum), but comfort is compromised.

Don Prather

Posted In: ACCA Now, Technical Tips

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