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BUILDING SCIENCE

Understanding the Impact of CSA P.9-11 on Combination System Design

By Brian Jackson

Complete P.9-11 Rated System

After the introduction of hydronic heating and instantaneous water heaters and boilers in the 1980s and early ’90s, there were countless issues that caused grief for builders, homeowners and manufacturers alike. In an effort to correct this legacy of mistakes, the CSA P.9-11 Standard was crafted.
CSA P.9-11 outlines a method to assess whether multiple Combo System components from the same or different manufacturers are working together to derive maximum system efficiency and to provide a standard metric to compare different system approaches.
Systems designers and builders have the freedom to match up components as they see fit to make a complete Combo System. Any hot water source—instantaneous water heater, boiler, combo unit and tank—can be combined with any fan coil—high or low velocity, multi-zone or single zone. The components can come from any manufacturer or mix of manufacturers. This can create problems if done without foresight.
Using this design approach doesn’t guarantee an efficient system even if two high-efficiency components are combined. Different components have different characteristics, which makes predicting system performance at varying loads near impossible.
For example, a 25,000 BTUH fan coil paired with a 120,000 BTUH condensing instantaneous hot water heating appliance with a 5:1 turndown ratio will operate reasonably efficiently at 100% heating load (which occurs approximately 10% of the heating season), but very poorly at most other conditions (which occurs 90% of the time).
Such “mismatches” affect ENERGYSTAR for New Home (ESNH) builders where CSA P.9-11 is a requirement. Building designers wishing to ensure compliance with ESNH can approach it in one of two ways: prescriptive or performance. The prescriptive method involves choosing a Builder Option Package (BOP)—a set of prescribed building details that when combined ensure compliance with the code.
The performance method is used when you do not or cannot comply with the standard set of details in the prescriptive method. In this application, a builder employs an energy-evaluating firm to model the building envelope to optimize energy efficiency by defining the building construction techniques and all construction details like insulation, architectural materials and mechanical equipment.
The CSA P.9-11 standard, applied to ESNH, permits use of the prescriptive method and the BOP optional points awarded will be defined in the standard based on the type of home and its location. Since the CSA P.9-11 standard applies to ESNH builders using combo systems, it is mandatory to use systems with a certified CSA P.9-11 result to be certified to ESNH. The system Thermal Performance Factor (TPF) number will define the system eligibility and whether optional points are awarded.
The trend toward smaller residences such as attached housing and multiple-unit buildings, with significantly smaller heating loads, can lead to a mismatch between the appliance capacity required for domestic water supply (at 120-200 MBH), and the smaller space heat loads of around 25 MBH. These two pieces of equipment work better when they’re more closely matched in capacity. A 25 MBH fan coil and matched with a 150 MBH instantaneous water heater will likely not work optimally and may give you a low TPF.

Immediately after the Standard adoption was announced there were implementation problems:
The manufacturers of equipment who needed to conduct the P.9 tests on their equipment found that there were not many labs that could complete the work, and only one in Canada.
For the manufacturers, the tests are expensive—upward of $10,000 per system. Moreover, not all builders build to ENERGY STAR and the standard at the time applied only to ENERGY STAR builders.
Natural Resources Canada (NRCan), the federal body that publishes the test results and determined the initial efficiency target, gave manufacturers six months to comply after releasing the TPF threshold.
There was not enough time to meet the initial deadline, which was, fortunately, extended. At the time of print there are 57 systems a designer can choose from and more are in the test phase.
The CSA P.9-11 requirement has now been adopted into Canada’s National Building Code as a minimum requirement with a relatively low TPF. It is being mentioned in some Provincial codes as well.
The rationale behind the CSA P.9-11 standard is sound. It defines your chosen system performance and efficiency and gives third party verification that the set of components will perform properly if applied correctly.

Manufacturers are working on the next generation of instantaneous water heaters and boilers that can modulate lower and maintain thermal efficiency at lower modulation levels to properly align with the smaller load requirements of the fan coil.

 

Brian Jackson is a professional engineer with 32 years experience in mechanical equipment design and systems application. With respect to CSA P.9-11, he ran the tests for Airmax/Flowmax Technologies, a manufacturing company that has a majority of the P.9-11 rated systems on the NRCan website.

 

 

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