Hydronic Balancing Part 1: The Standards and Driving Force Behind the New Requirements

By Chad Edmondson

Balancing plays a critical roll in the performance of any hydronic heating and cooling system.  For that reason alone, ASHRAE has made hydronic balancing a non-negotiable stop on the road to compliance with ASHRAE 90.1-2010 (or 2013), starting with this requirement:

6.4.2.2 Pump Head. Pump differential pressure (head) for the purpose of sizing pumps shall be determined in accordance with generally accepted engineering standards and handbooks acceptable to the adopting authority.  The pressure drop through each device and pipe segment in the critical circuit at design conditions shall be calculated.

Furthermore, systems must be balanced:

6.7.2.3 Hydronic System Balancing.  Hydronic systems shall be proportionately balanced in a manner to first minimize throttling losses; then the pump impeller shall be trimmed or pump speed shall be adjusted to meet design flow conditions.

And finally, there is this:

6.7.2.3.1 General. Construction documents shall require that all HVAC systems be balanced in accordance with generally accepted engineering standards. Construction documents shall require that a written balance report be provided to the building owner or the designated representative of the building owner for HVAC systems serving zones with a total conditions area exceeding 5000 ft2.

All of these standards are interrelated.  Accurately calculating pressure drops ensures that pumps are not oversized.  Oversized pumps can lead to inefficient pump operation over the life of the system.  Flow balancing (during and after commissioning) is how we make sure that we only put as much energy into the system as we are take out.  Flow balancing is also how we begin to benchmark the performance of our buildings, a practice that ASHRAE aspires to make commonplace.  It is all part of a long-term plan to drive more and more buildings to net zero energy performance.  

In all likelihood the standards as written above are now part of your own building code since the U.S. Department of Energy (DOE) has required that states update their building codes to meet or exceed Standard 90.1-2010 (or ask for an extension) by October 18, 2013. 

What does this mean to mechanical engineers designing commercial buildings larger than 5000 sq. ft.?   Among other things, it means that you must now incorporate a balancing procedure into your mechanical specifications and include in the design plan all the necessary instrumentation to perform that procedure.

Over the next several blogs we’ll dig deeper into what you, as a designer or as a commissioner, need to know and understand in order to meet the balancing standards of 90.1- 2010 (and 2013).