2021 IECC Sections C407 and C408

Lesson 12: Total Building Performance and Commissioning

IECC C407, C408 · 14 practice questions

0:00 / --:--

Reading

Most buildings are checked one requirement at a time, but the code offers a second way to comply, total building performance, in which a simulation of the whole building has to beat a reference version of it. Whichever path is used, Section C408 then asks a different question: does the finished building actually work the way the drawings said it would? That is commissioning, and it ends in paper the code official and the owner can check. This lesson summarizes Section C407 and then follows the C408 sequence step by step. Local adoption governs which edition applies (see Lesson 1).

The commissioning sequence. The report reaches the code official before the final inspection is accepted, and the balancing and final reports follow to the owner after the certificate of occupancy.

Three ways to comply

A commercial building complies by one of three routes (C401.2). The prescriptive route follows Sections C402 through C406 and C408, which is what Lessons 3 through 11 taught (C401.2.1). The total building performance route follows Section C407 (also C401.2.1). The third route is ANSI/ASHRAE/IES Standard 90.1 (C401.2.2), which this course only points to. Commissioning under C408 belongs to the prescriptive route and is also on the mandatory list of the performance route.

What total building performance compares

The simulation covers heating, cooling, service water heating, fan systems, lighting power, receptacle loads, and process loads, and leaves out energy used to charge vehicles for on-road use (C407.1). The proposed design must have an annual energy cost no greater than 85 percent of the standard reference design (C407.2). If the reference design costs $60,000 a year, the proposed design may cost at most $51,000, and $52,300 fails. Prices come from a source the code official approves, and the code official may require time-of-use pricing. The savings credited to on-site renewable energy may not be more than 5 percent of the total energy cost. Jurisdictions that measure site energy (1 kWh = 3413 Btu) instead of cost are excepted.

What stays mandatory

Choosing the performance route does not switch off every rule. Table C407.2 lists the sections that still apply: envelope air leakage (C402.5), the load calculation and system design rules, equipment efficiencies, most HVAC controls, ventilation, fans, and HVAC construction under Section C403, all of Section C404, all of Section C405 except C405.3, and Section C408. Envelope insulation and glazing values, and the interior lighting power allowance, are not on the list, so the simulation may trade them against savings elsewhere in the building.

Software, report, and approval

Permit submittals must include a compliance report with the building address, an inspection checklist of the proposed design's characteristics showing the annual cost of both designs, the preparer's name, and the software name and version (C407.3.1). The code official may also ask for zoning diagrams, the complete input and output files, and a builder's certification (C407.3.2). The software must model 8,760 hours of operation and weather, at least ten thermal zones, thermal mass, part-load equipment curves, and hourly variations in occupancy, lighting, and receptacle loads, and must print the inspection checklist (C407.5). Tools tested to ASHRAE Standard 140 may be approved, and anything the software cannot model needs an exceptional calculation method the code official approves (C407.5.1 and C407.5.3). The printed checklist becomes the field inspector's list of what to verify.

Who commissions, and which systems

Before the final mechanical and plumbing inspections, a registered design professional or approved agency must provide evidence of commissioning for mechanical and service water-heating systems (C408.2). The drawings must carry notes describing the commissioning provisions, and copies of the documentation go to the owner and are available to the code official. Two exceptions apply: buildings whose total mechanical equipment capacity is under 480,000 Btu/h of cooling and under 600,000 Btu/h of combined service water and space heating, and economizer systems (Section C403.5) that serve individual dwelling or sleeping units. Owner operation and maintenance documents, and a visible maintenance label on equipment, are required separately (C408.1.1).

Worked example. A 6,000 square foot clinic has 25 tons of cooling (25 x 12,000 = 300,000 Btu/h), 250,000 Btu/h of gas space heating, and a 150,000 Btu/h gas water heater, so heating and water heating together are 400,000 Btu/h. Both totals are under the limits, so the clinic is exempt from C408.2. Add a second unit that brings cooling to 500,000 Btu/h, and the exemption is gone, because the cooling limit of 480,000 Btu/h (40 tons) is passed.

The plan and balancing

The commissioning plan, written by the registered design professional or approved agency, names the activities in each phase and who does them, lists the equipment to be tested and the tests, identifies the functions to be tested such as calibrations and economizer controls, states the conditions for testing (winter and summer design conditions and full outside air), and gives measurable performance criteria (C408.2.1). HVAC systems are then balanced by measuring air and water flow and adjusting to design (C408.2.2). Air systems need a means for balancing at each supply outlet and zone terminal, and discharge dampers are prohibited for balancing constant-volume fans and variable-volume fans with motors of 10 hp and larger. Balance by cutting throttling losses first, then adjust fan speed for fans over 1 hp. Hydronic coils need a means of balancing and measuring flow, and throttling is minimized before the impeller is trimmed or the pump speed changed. Fans with motors of 1 hp or less need no means for air balancing (C408.2.2.1), and pumps with motors of 5 hp or less need no means for balancing or measuring flow (C408.2.2.2).

Functional tests and reports

Functional performance tests show that equipment, controls, and system-to-system interfaces work as the plans and specifications say: every mode in the sequence of operation, at full and part load, redundant or backup mode, alarms, and the response to loss and restoration of power (C408.2.3.1). One exception covers unitary or packaged equipment from the Section C403.3.2 tables that does not need a supply air economizer. Controls must be calibrated and their sequences tested (C408.2.3.2), and air economizers must be functionally tested (C408.2.3.3).

The results go into a certified Preliminary Commissioning Report given to the owner, with mechanical and water heating findings in separate sections. It includes the completed compliance checklist, the deficiencies not yet corrected, the tests deferred and the climate they need, the test results, and the procedures and pass criteria used (C408.2.4). A building is not acceptable for final inspection until the code official has received that report (C408.2.4.1). Then, within 90 days of receiving the certificate of occupancy, the owner gets the balancing report and a Final Commissioning Report giving results, how each deficiency was resolved, and the procedures with their pass criteria (C408.2.5). Deferred seasonal tests are the one exception to the final report content.

Key numbers

Performance path: proposed annual energy cost at or below 85 percent of the reference (C407.2)
Software: 8,760 hours and ten or more thermal zones (C407.5)
Commissioning exempt below 480,000 Btu/h cooling and 600,000 Btu/h combined heating (C408.2)
Test conditions: winter and summer design and full outside air (C408.2.1)
No discharge dampers for balancing fans of 10 hp and larger (C408.2.2.1)
Preliminary report before final inspection; final documents within 90 days of the certificate of occupancy (C408.2.4.1, C408.2.5)
Occupant sensors: 7 or fewer test each; more than 7 test at least 10 percent and not fewer than one per combination (C408.3.1.1)

Lighting controls testing

Before final inspection the registered design professional or approved agency must show the automatic lighting controls were tested (C408.3.1). For occupant sensors, a project with 7 or fewer tests every sensor. With more than 7, test each unique combination of sensor type and space geometry, at least 10 percent of each combination and never fewer than one, and if 30 percent or more of the tested sensors fail, test all the remaining identical ones (C408.3.1.1). Example: a building has 35 sensors in three combinations of 20, 10, and 5. The minimum tested is 2 + 1 + 1 = 4. If one of the two tested in the group of 20 fails, that is 50 percent, so all 20 in that group get tested. Time switches are checked for correct weekday, weekend, and holiday schedules, battery backup, an override limit of no more than 2 hours, and occupied and unoccupied behavior (C408.3.1.2). Daylight controls are checked for location, calibration, response, and restricted access to calibration (C408.3.1.3). Drawings, an operation and maintenance manual, and a test report reach the owner within 90 days of the certificate of occupancy (C408.3.2).

In the field

Commissioning paperwork gets lost at the end of a job, so GCHS plan review looks for it at the start. Does the drawing note say who commissions and what the plan covers? Is the system below the exemption or above it? The inspector then asks for the Preliminary Commissioning Report before signing off the final. If the tests that need cold weather are deferred in a Gulf Coast summer, the report must say which tests, and what weather they need, so the deferred work is not forgotten. The last check is the 90-day promise: owner documents that never arrive are a common gap after move-in.

Practice questions

1. A designer uses the total building performance path, and the standard reference design has an annual energy cost of $60,000. What is the most the proposed design's annual energy cost may be under Section C407.2?

$54,000
$57,000
$60,000
$51,000

2. Under Section C407.1, which loads must the total building performance analysis include?

Heating and cooling only, because lighting and the other loads are regulated in separate sections of the code
Heating, cooling, service water heating, fans, lighting power, receptacle loads, and process loads
Envelope, heating, and cooling loads, with lighting and receptacle loads left out of the analysis
All of those loads plus the energy used to charge vehicles for on-road transportation

3. A designer chooses total building performance under Section C407. Which requirement stays mandatory according to Table C407.2?

Thermal envelope air leakage (C402.5)
The interior lighting power allowance (C405.3)
The insulation R-values of Table C402.1.3
The additional efficiency credits of Section C406

4. Under Section C407.3.1, which item must the compliance report for a performance-path permit include?

The contractor's license number and bid price
A signed statement from the utility that energy rates will not change
The name and version of the compliance software tool
A copy of the commissioning plan for the mechanical system

5. What must the software used for total building performance be able to model under Section C407.5?

A typical summer day and winter day, with one thermal zone per floor
A full calendar year of 8,760 hours, with ten or more thermal zones
Twelve monthly averages, with at least two thermal zones
Peak demand only, using a single design-day weather file

6. An inspector reviews a new 6,000 square foot clinic with 300,000 Btu/h of cooling, 250,000 Btu/h of gas space heating, and a 150,000 Btu/h gas water heater. Does Section C408.2 require commissioning evidence?

No, cooling is under 480,000 Btu/h and combined heating and water heating is 400,000 Btu/h, under 600,000
Yes, because the building has both heating and cooling equipment
Yes, because any system over 20 tons must be commissioned
Yes, because the water heater alone is over 100,000 Btu/h

7. Which testing conditions must a commissioning plan affirm under Section C408.2.1?

Spring and fall shoulder-season conditions only
Only the conditions on the day the balancer visits the site
Design conditions for the coldest day recorded in the last five years
Winter and summer design conditions and full outside air conditions

8. Who develops the commissioning plan under Section C408.2.1?

The mechanical contractor's field foreman working with the test-and-balance technician
The building owner's maintenance staff after the certificate of occupancy is issued
A registered design professional or an approved agency
The code official who reviews the permit and performs the final inspection

9. A test-and-balance technician proposes to balance a 15 hp variable-volume supply fan by closing its discharge damper. What does Section C408.2.2.1 say?

That is not allowed, because discharge dampers are prohibited for balancing variable-volume fans of 10 hp and larger
It is allowed, because discharge dampers are the required balancing method for any fan over 1 hp in size
It is allowed if the damper is closed no more than halfway, which limits the throttling losses
It is not allowed, but only for fan motors of 25 hp and larger, since smaller fans may use dampers

10. Which condition must equipment functional performance testing cover under Section C408.2.3.1?

Only the normal mode of the sequence of operation, tested at full load
The mode of operation on loss of power and on restoration of power
Only part-load operation, since full load is already covered by air balancing
Only the factory startup steps listed in the manufacturer's checklist

11. A contractor asks for the final mechanical inspection on a building that requires commissioning, but the code official has not received the Preliminary Commissioning Report. What does Section C408.2.4.1 say?

The inspection proceeds, and the report is due later with the certificate of occupancy at the end of the project
The inspection proceeds if the balancing report is on the job site
The report is due 90 days after the final inspection
The building is not acceptable for final inspection until the code official receives the report

12. The cooling-season tests on a new building's chilled-water system cannot be run in January. Where must this appear under Section C408.2.4?

Nowhere in the paperwork, because a test that cannot be run for climate reasons is optional and needs no record
Only in the Final Commissioning Report, since the preliminary report covers just the tests that were completed
In the Preliminary Commissioning Report, which lists deferred tests and the climatic conditions needed to run them
Only in the plan review comments, because deferred tests are settled during permit review and are not part of testing

13. The construction documents must require the balancing report and the Final Commissioning Report to reach the owner within what period, according to Section C408.2.5?

30 days after receiving the certificate of occupancy
90 days after receiving the certificate of occupancy
180 days after receiving the certificate of occupancy
Before the certificate of occupancy is issued

14. A building has 35 occupant sensors in three unique combinations of sensor type and space geometry, with 20, 10, and 5 sensors. What is the minimum number tested under Section C408.3.1.1 before any failures?

4 sensors, which is 2 from the group of 20 and 1 each from the groups of 10 and 5
35 sensors, because a project with more than seven must test them all
3 sensors, one for each combination regardless of size
7 sensors, the number tested on small projects

Glossary

Total building performance: A compliance path in Section C407 where a simulated proposed design must use no more than 85 percent of the annual energy cost of a standard reference design.
Standard reference design: The code-defined version of the building that the proposed design is compared against in the energy simulation.
Commissioning: The planned process of testing and adjusting building systems so they perform as designed, documented under Section C408.
Commissioning plan: The written list of systems, tests, conditions, people, and pass criteria prepared before testing begins (C408.2.1).
Functional performance test: A test showing that equipment and controls work in every mode of the sequence of operation, including alarms and loss of power (C408.2.3).
Preliminary Commissioning Report: The certified report with the compliance checklist that the code official must receive before a building is acceptable for final inspection (C408.2.4).
Final Commissioning Report: The report of results, resolved deficiencies, and procedures delivered to the owner within 90 days of the certificate of occupancy (C408.2.5.2).
Test and balance: Measuring and adjusting air and water flows to design values, minimizing throttling losses before changing fan speed or trimming pumps (C408.2.2).

Previous lesson Back to course Mark lesson complete Next lesson