Whole House Ventilation Strategies

SystemVision, ENERGY STAR® and other green programs require ventilation for improved indoor air quality.  As we build homes tighter and tighter, good ventilation becomes more and more important.  Ventilation can be divided into spot ventilation, such as bath and kitchen exhaust fans, and whole-house ventilation.  This month we will concentrate on different whole-house ventilation techniques.

Supply Ventilation

Most SystemVision builders use supply ventilation, as this system is the most cost effective way to safely provide whole-house ventilation.

Supply VentilationImportant items to remember:

  1. Outside air intake must be 18 inches off of the ground, 10 inches above roofing material (through the roof) and 10 feet away from exhausts and plumbing vents.
  2. Fresh air line must be dampered and filtered.  Filter must be accessible from inside of the home.
  3. Short, straight runs lead to success.  If you consistently have trouble meeting the standard with a 6-inch duct, increase to an 8-inch duct.
  4. Amount of ventilation must be equal to: (7.5 CFM)(number of bedrooms + 1) + (.01 CFM)(sq. ft. of conditioned space)

*All specs and the cut sheet above can be found in the HVAC section of the SystemVision notebook

Version 3.0 of ENERGY STAR will not allow the SystemVision supply ventilation set-up as an acceptable means of ventilation unless it is modified to meet the following standards:

  1. System must be designed to operate intermittently and automatically based on a timer for at least 144 minutes per day.
  2. System must restrict outdoor air intake when not in use (e.g., motorized damper).
  3. Fresh air intake must be protected by a screen with no greater than 0.5 inch mesh and must be located 2 feet above the grade/roof deck in Climate Zones 3 & 4 and 2.5 feet in Climate Zone 4 (these values are for N.C. only).
  4. Air handler fan speed must be ECM/ICM, variable speed and run at a reduced speed during ventilation, or include a controller (e.g., smart cycler) that reduces the ventilation run time by accounting for hours when HVAC system is heating or cooling.
  5. Ventilation controls for occupant must be provided.
  6. The ventilation must be tested and documented.

If you are interested in meeting ENERGY STAR 3.0 ventilation requirements or improving your ventilation strategy, then improved supply ventilation or an energy recovery ventilator (ERV) may be a good option. 

Improved Supply Ventilation

If you follow the requirements for the ENERGY STAR 3.0 supply ventilation, the system allows ventilation to take place more often than just when the air conditioning or heat system is running by turning on the air handler blower to circulate fresh air.  The downside to this is that when the blower turns on to ventilate the home and the air conditioner or heat is not on, it can cause comfort issues by delivering humid, hot or cold air to the home.

We do not believe in installing a ventilation system that can cause comfort or moisture related issues. For that reason, SystemVision will require a ventilation control system.  A ventilation control system provides a motorized damper, humidity and temperature sensors, and occupant ventilation controls.  The ventilation control system monitors indoor and outdoor conditions to ensure the system only ventilates the home when it will not cause comfort issues.

In order to satisfy ENERGY STAR 3.0 and SystemVision requirements and provide comfort to the occupants, an improved supply ventilation system will include:

  • Items required for SystemVision
    • Correct flow
    • Filter accessibility from the conditioned space
    • Insulated fresh air line
  • Items required for ENERGY STAR
    • See items above (1-6)
  • Items required for comfort/durability
    • Control system that only ventilates when the outside conditions will not negatively affect the indoor air quality and comfort

Energy Recovery Ventilator

An energy recovery ventilator (ERV) uses its own fan system to provide continuous or intermittent ventilation to a home. It offers improved ventilation and energy efficiency when compared to other ventilation systems. ERVs exhaust stale air while simultaneously bringing in fresh outdoor air.  In this process, the outside air is conditioned to the same properties (temperature and humidity levels) as the inside air.

An ERV is an excellent choice for ventilation but is often more expensive than the improved supply ventilation system.

Balanced Ventilation

ERV "Guts"

Balanced Ventilation

ERV

If you are planning to use an ERV please read the following article: http://www.advancedenergy.org/buildings/knowledge_library/ventilation/erv.pdf

If you have any questions about ventilation, join our conference call Thursday, Nov. 17 at 11:00am.  As always, if there is a topic you would like covered in the blog, let me know!

To register for the conference call:  https://www3.gotomeeting.com/register/284697758

Category: Ventilation   

 

There are 2 Comments About This Post

 

George Reynolds Says,

I have heard that ASHRAE will allow bathroom fans with timers switches in parallel with the wall switch as acceptable techniques to meet the 62.2 criteria. Also is the 62.2 cfm a minimum or absolute number?

on December 20, 2011 at 07:07 PM
 
 

DTreleven Says,

George,

62.2 is a minimum number. However, you must remember that ventilation is an energy penalty so you must weigh the benefits of more ventilation versus the additional energy required for ventilation. Where this cut-off point will vary from homeowner to homeowner. In SystemVision, we treat this more as an absolute and shoot to ventilate as close as possible to 62.2.

ASHRAE 62.2 can be satisfied by exhaust, supply or balanced ventilation. We require supply or balanced for our program for a few reasons. First, we cannot measure how much ventilation we are actually receiving based on an exhaust only strategy. So ventilation is at best a guess. Secondly, we are unsure where the ventilation air is coming from. We want to know that our ventilation air which is intended to be fresh air is still fresh as it enters the home. Lastly, with our humid climate we want to condition the air prior to it entering the home for comfort and durability reasons.

I hope I answered your questions.

Best,
David

on December 20, 2011 at 09:03 PM
 

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