Reviewer Tips: NECB 2011 Hydronic Pumps

In some LEED v4 BD+C projects using the Canada ACP – NECB, unexpectedly high pump savings have been noted. (The ACP allows a percentage improvement in the proposed building performance rating compared with the baseline according to the National Energy Code of Canada for Buildings (NECB) 2011.)

Most of the issues identified have to do with the reference building hydronic pump size in cases when the hydronic pump power for the reference building was modelled identically to the proposed building.

NECB 2011, Section 8.4.4.15.(2), states “Where the proposed building uses more than one pump in a given hydronic system, the peak shaft power demand of the reference building’s pump shall be modeled as being identical to the combined peak shaft power demand of the proposed building’s pumps. (See Appendix A.)”. Moreover, Appendix A of the section gives an example on how to calculate the pump head of the reference building hot water pump assuming the same heating capacity for the proposed building and reference building and therefore, the same shaft power pump.

However, what does pump power demand mean? Should the reference pump power be modelled the same as the proposed case? This misinterpretation is resulting in modeling errors having a significant impact on the total building savings.

As explained by the Release Notes for CAN-QUEST NECB v1.1 (06/09/2016)¹, “Given the mismatch between zones and systems in the proposed and reference cases, there can be dramatically different flow rates for the hydronic loops between the proposed and reference cases. Therefore, the sum of the power for all pumps is divided by the design flow to calculate the proposed building’s (W/(L/s)); the same value is used to determine the pumping power for the reference case (rather than matching the peak shaft demand, in W, between the proposed and reference cases).” This approach is in line with the NECB 2011, Section 8.4.4.15.(3), which states “Where the total static head or efficiency of the proposed building’s hydronic pump is not known, the characteristics of the reference building’s hydronic pump shall be based on the peak power demand, in W/(L/s), of the proposed building’s pump.”

Therefore, in situations where the proposed building used more than one pump in a given hydronic system, it is the power per flow rate (W/(L/s)) that must match between the Reference and Proposed cases, not the peak shaft demand (W). For clarity: modellers must sum the power for all applicable pumps in the Proposed design and divide it by the Proposed design flow² rate serving the “primary systems” (as referenced in 8.4.4.9.(6),(e)) in order to determine the pumping power for the Reference building. The primary systems include coils, radiators, baseboards, etc., served by the central heating or cooling source – often referred to as a “secondary circulation loop” (e.g., a hot water loop circulating hot water between a heat exchanger and periphery heating coils and baseboards, which excludes the “primary loop” circulating hot water between the boilers and heat exchanger).

Footnotes

¹ Release Notes for CAN-QUEST NECB v1.1 is available upon request at info.services@nrcan-rncan.gc.ca or 1-877-360-5500 (toll-free) (613-992-3245 in the National Capital Region).

² The design flow is the supply fluid from heating or cooling source to all heat transfer devices (coils, radiant panels, and baseboards, for example) at design conditions.