- Video Introduction of the New Aztec AMC Evaporative Cooling Air Turnover System
- Designing Data Centers as Thermos Bottles
- A New Video on YouTube Describing How the Aztec Evap System Works
- Aztec To Be In Capacity North America Exhibit Hall
- Virtual Reality
- A Simple Concept That Saves Big Dollars
- Indirect Evaporative Cooling Research Project Launched
- Canadian Patent Granted for Mestex Digital High Turndown Burner
- So You Think Your Critical HVAC System Is Reliable?
- Aztec Provides Fresh Air Intake Penthouses for Data Centers in Northwestern US
- Shading and Make-Up for Building Designers
- Credibility and Trust
- How I Spent My Summer Vacation
- Too Hot to Handle? A Simple Reminder.
- Preaching to the Choir
- Evaporative Cooling Anaysis for Data Modules in Two Diverse Climates
- Aztec Indirect Evaporative Cooling System on Display at DFW ASHRAE Golf Outing
- How We Used To Do It
- Air Pollution and HVAC
- Mestex, Division of Mestek YouTube Channel
- Aztec Evaporative Cooling for Data Centers at Data Center World
- GreenBuild Toronto
- Trane Division of Ingersoll-Rand in Lawsuit Over Wireless Technologies
- New BIM Objects From The Aztec Brand
- DOE Proposes Building Rating System
- The Importance of Correct Static Pressure for Direct Fired Make-Up Air Equipment
- Instant Online Document Lookup Using Microsoft Tags
- Do Evaporative Cooling Systems Use Too Much Water?
- Sustainability at Mestek Dallas
- Facebook Offers Their Outside Air Cooling Solution To All Data Center Owners
- Restaurant Energy Saving Idea That Can Be Used Anywhere
- Planning for Volatility
- Ever Wonder Where the Power Goes in a Data Center?
- ASHRAE TC 9.9 Expands Data Center Temperature Ranges Again
- Green Buildings Get Another Boost
- ASHRAE Show Report
- CFD, Air Turnover, and the Pharmaceutical Industry
- It is not sustainable if it is not maintainable... or if it breaks down
- Accounting Rule Change Might Impact HVAC
- Reduce electrical demand load with an Aztec indirect evaporative cooling unit
- Lower Cost of Ownership with the Applied Air FAP
- Everything You Want to Know in a Flash
- Data Centers and Evaporative Cooling Webinar August 23
- New "Green" Product Announcement
- DDC Application Case Studies
- PowerPoint showing the importance of gas pressure, static pressure, and voltage
- Webinar: 'The Importance of Correct Gas Pressure, E.S.P. and Voltage'
- An Old Solution to a New Problem
The Story of SHR or Why My Classroom is Stuffy
Did you ever wonder why a dedicated outdoor air system ("DOAS") is important for a school building?
The reason is something called the "SHR". What is an "SHR" you ask? "SHR" stands for "Sensible Heat Ratio" and it is a way to determine how much of the total capacity of an HVAC unit is used for sensible cooling versus latent cooling. As you know, the latent cooling ability of an HVAC unit determines how well it can dehumidify the air it is supplying. In a perfect world the design team would select an HVAC unit with an SHR that exactly matches the SHR of the space it is trying to temper. However, our world is not perfect and has actually gotten more "imperfect" over the last decade.
What has occurred is a change in both standard HVAC equipment and classrooms. In the drive to reach higher and higher levels of efficiency, equipment manufacturers have been increasing coil surfaces and increasing the ratio of sensible cooling to latent cooling...creating a higher SHR. Years ago packaged HVAC equipment had SHRs in the range of 0.5 to 0.7. If you surf the Internet and look at the specifications of small packaged equipment today you will find SHRs of 0.7 to 0.8...meaning only 20% or 30% of the capacity of the unit is available for controlling latent heat.
In the meantime, programs such as LEED have created tighter and tighter buildings with shell loads that become almost insignificant. Since the shell loads are all sensible you can begin to see the developing problem. If you then cram more students in a classroom, as is common in most school districts, the latent contribution from student respiration goes up and the overall classroom SHR goes down. Throw in the ASHRAE 62.1 ventilation air requirement that is also heavy on latent contribution and the result is a typical classroom that could have an SHR of 0.60 to 0.65.
As a general rule...any time the SHR of the space is lower than the SHR of the HVAC equipment serving the space then the humidity level of the space will increase.
Since the packaged HVAC equipment controls respond to sensible heat (a conventional thermostat) the result is a unit that shuts off before enough moisture is removed from the air and the room becomes "stuffy"...or the teacher lowers the room setpoint to force the HVAC unit to run longer and the result is wasted energy and a cold room.
The solution is to take the outside air component out of the classroom units, reducing their sensible heat capacity to match the sensible heat load of the space, and put the ventilation air into a dedicated outdoor air system ("DOAS"). A well designed DOAS will be created from the start to dehumidify the air before it gets to the classroom, leaving only student respiration for the packaged HVAC room equipment to handle. This concept puts the HVAC SHR and room SHR in much closer balance and gets us closer to that "perfect world".