Tag: dew point

Indoor Dew Point: Maintaining Thermal Comfort, Avoiding Building Damage

Posted on by Lindsey Burbee

Condensation and Moisture Risks in Buildings

Condensation, moisture absorption and, subsequently, mold or organic growth are often a result of high indoor dew point combined with cool surface temperatures. For example, if a facility’s indoor dew point is above 60oF, it is possible that moisture will begin to condense on cool surfaces like ductwork, chilled water supply lines, windows, or refrigeration systems. This collection of moisture can cause damage to the building, as well as to merchandise. It can even promote organic growth over time.

 

 

 

In addition to the risk of moisture accumulation, ASHRAE recommends maintaining a dew point below 62 oF to meet thermal comfort for approximately 80% of occupants; a dew point of 45 oF is recommended to maintain summertime humidity comfort levels.

 

 

Monitoring Dew Point

Consider this: You are a kid in a candy store with a plethora of delicious options in front of you. You sort through the store and boil your decision down to two candy bars.

Option A: The tried and true milk chocolate bar. Nothing fancy but classically delicious.

Option B: Fluffy nougat topped with caramel and peanuts, coated in milk chocolate. An exciting snack bursting with flavor.

Did you choose Option A or Option B?

If I had to guess, you chose Option B as it gives you more variety with your purchase! Now, what if I told you that the decision you just made also can apply to thermal HVAC design and dew point monitoring principals?

Option A: A design principal of maintaining 60% relative humidity (RH).

Option B: A design principal of maintaining a 60oF dew point.

Both are similar and help maintain a healthy building, but maintaining a 60oF dew point (Option B) is inherently better and offers a more reliable risk indicator. Using 60% RH as an indicator (Option A) is unreliable as it creates needless concern when air temperature is cool. In the example below, you can see that the amount of water vapor in the air remains the same while relative humidity concentration varies depending on the temperature of the air.

 

 

Image Source

 

Conversely, a facility manager or building owner may have a false sense of security when indoor air temperature is above normal levels because relative humidity will decrease as air temperature rises. These reasons are why dew point should be used as a threshold of concern. Dew point will not only factor in moisture content and temperature of the air but also provides a risk indicator for condensation and moisture absorption, which should be a facility manager’s primary concern.

 

 

Using Indoor Dew Point as a Risk Indicator

If you are already using indoor dew point as a risk indicator for indoor moisture activity, then continue to do so! Specifically, look to ensure that indoor dew point remains below 60 oF during cooling operations to reduce the risk of moisture absorption, condensation, and organic growth.

If you are not using indoor dew point as your risk indicator, now is the time to do so! You could be surprised to learn that measuring relative humidity alone may not be keeping your facility safe.

If you are already noticing signs of moisture accumulation, mold or organic growth, then ASHRAE recommends implementing the following HVAC factors to reduce your risk:

 

  • Dehumidify ventilated air to a dew point below the indoor dew point during cooling.

  • Drain HVAC system condensation effectively to prevent water buildup.

  • Prevent indoor surfaces from cooling below the indoor dew point in both occupied and unoccupied modes.

  • Keep indoor dew point low enough to stop condensation on HVAC components, building materials, or furnishings.

  • Install and control humidifiers correctly to avoid adding excess moisture to the air.

  • Insulate HVAC and plumbing components so their surfaces stay about 10°F above the indoor dew point.

These simple steps — in addition to proper HVAC ventilation, indoor air monitoring, indoor air verification, and keeping an eye on seasonal changes — can help ensure that your facility is operating in a safe manner while reducing risk of mechanical damage, moisture accumulation, or organic growth.

If you would like to learn more about ways in which your indoor air environments can be improved, please reach out to us. Please complete our contact form or contact us by phone at (513) 965-7300.

Window condensation is a sign of Indoor Dew Point

Air Balance Basics for Existing Facilities

Posted on by Lindsey Burbee

We understand the concept of the “band-aid approach” whereby you find a quick cover-up to a problem without actually investigating the root of the it.  This concept applies frequently to Facility Managers or Building Owners wrestling with HVAC emergencies being caused by negative building pressure. They tackle issues such as condensation, hot/cold spots, humidity, odor, and difficult to open doors with “band-aids”. These “band-aids” are in the form of increased air conditioning, dehumidifiers, wet floor caution signs, door mechanisms, air fresheners, apologizing to patrons, comping customers’ bills, and so on.  This is understandable when you’re managing 80+ facilities, all with problems that stretch far beyond just HVAC.  However, it comes with a cost of spending a lot of time, money, energy, and reputation just to have the issues continuing to come back.  While balanced airflow is not a tangible product, the consequences of an unbalanced building are very perceptible.

Facility Managers are ready to de-mystify their HVAC issues by understanding the root causes.  Use the air balance basics below to recognize when an issue is airflow related.

What does it mean to have a balanced airflow?

Think of financial statements with income listed in one column and expenses in the other.  Much like a budget, you want incoming cash coming to be equal to or greater than cash going out. You typically want the air going into a building to be slightly greater than the air going out.  Similarly, think of a balanced scale.  In the graphic below, air is being drawn out of the building by exhaust fans at a rate of 4000 CFM (cubic feet per minute). This is to remove heat and smoke from kitchen cooking appliances and foul air from the restrooms. Air is also being introduced into the building through an outside air fan, at a rate of 4500 CFM. This is to provide fresh breathing air for the occupants and to replace the exhausted air.  The result is a slightly positive building pressure of 500 CFM (4500 – 4000 = 500), which signifies a balanced airflow.  Conversely, if air coming into the building is slightly less than the air leaving the building, then you have a negative building pressure, which is the frequent culprit of many HVAC problems.

Which brings us to a crucial pairing to the air balance concept.  That is if balanced airflow is peanut butter, then a performance test is the jelly.

What is an air test & balance service?
 

Air balance testing is the process of measuring HVAC airflow performance.  Once tested, the systems are then adjusted, or balanced, so the air brought into a building is slightly greater than the air being pulled out of the building.  The benefit for testing and balancing being a combined service is explained by Rob Falke, President of the National Comfort Institute, “This [positive] pressure condition can be designed, but to be sure it actually happens requires air diagnostic testing.  However, it’s hard to say how great the positive pressure reading in the building will be. It depends on how tight (or leaky) the envelope of the building is, and what other pressure generating forces exist, including the wind, appliances, exhaust fans, and the stack effect of the building.”  The result is a comfortable, healthy indoor environment with an HVAC system that is optimized to perform efficiently.

 Sources:

  • Digital image. Air Concepts LLC. N.p., n.d. Web.  Nov 25, 2015.
  • Falke, Rob. “How to Measure Building Pressures.” Contracting Business, 1 May 2006. Web. 25 Nov. 2015.