ASHRAE 36 – High – Performance Sequences of Operations for HVAC Systems – “Trust but Verify”
In 2018, ASHRAE released a new guideline which has been years in the making and is based largely on (Research Project) RP-1455 research. The purpose of the guideline is to provide a standard for the development, implementation, and commissioning of the sequence of operations for HVAC systems. This original release deals mainly with Variable Air Volume (VAV) equipment with plans to cover additional mechanical cooling and heating equipment in future addendums. The main purpose of the guideline is to develop a standardized way to specify, commission, and operate a set piece of equipment, as it pertains to its control logic, so it provides optimum efficiency right out of the box. The guideline lists specific operating parameters and control sequences which are all based around the premise of having the equipment operate according to other ASHRAE guidelines, namely 62.1 Ventilation for Acceptable indoor Air Quality and 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings. By standardizing on the control sequences for mechanical equipment (specifically VAV boxes) there are a number of benefits that can be realized, as called out in the guideline.
Reduced engineering time
Reduced programming and commissioning time
Reduced energy consumption (right out of the box)
Improved indoor air quality
Reduced system downtime (by including diagnostic software)
Provide a standardized package understandable across multiple disciplines
Essentially engineers, when specifying the control of a VAV box, could simply refer the controls contractor to ASHRAE 36 for the necessary set points and sequences. Likewise, programming could be a ‘canned’ program that provides adequate control right from the factory. In theory, commissioning could also be a non-issue once the guideline sequence is proven out and the industry is comfortable with how it operates. That does all sound great, and for the control of VAV boxes or for less critical, or stand alone, cooling applications, that may be acceptable, but for cooling a critical data center, a lot more attention and thought should always be required. This standard does have great potential to reduce the overall process of specifying, designing, manufacturing, installing, and commissioning certain equipment, but I tend to follow the “Trust but Verify” approach, especially for the more critical installations. True it is still in its infancy, and at this point only pertains to VAV boxes, but the plan would be to include all types of air conditioning equipment, and I don’t see why it would not extend, eventually, to some data center equipment. Chiller plants and Data Center cooling could potentially be included in this guideline with canned sequences standardizing equipment control across the board. I do understand that standardization could provide for a quicker and potentially better finished product from the manufacturer, but I would still err on the side of caution and completely commission what was installed.
It kind of falls under the same premise as to why we conduct factory witness testing on critical equipment: to ensure the equipment, as manufactured, operates as designed before it is shipped from the factory. Same holds true for on-site commissioning of your mission critical cooling, however this type of commissioning requires that all systems (not just individual equipment) operate as a whole, per the design, before the project is closed out. The individual equipment could be manufactured and tested at the factory and operate under the standardized sequence seamlessly, but this is only half of the picture. In addition, and most importantly, the true test is on site where all equipment is tested as a whole to ensure all systems operate cohesively with other equipment, sensors, controllers, actuators, field wiring, etc. This type of testing can only be fully proven out in the field when entire systems are up and running and fully integrated. It is at this time you can actually see what happens as each individual piece of equipment interacts with the system. It is here that changes may need to be made and/or setpoints tweaked as determined by the system effects, regardless of the standard sequence. Using the standardized sequence for individual equipment operation would definitely provide some benefit in the commissioning process but would not, in my opinion, replace what truly is required to successfully prove out the operation of a complete mission critical system.
I do believe this guideline is on the right path to provide better, more efficient systems, and believe it could be most beneficial in the spaces that require less critical cooling. I do also feel that even though this is a standard that could potentially reduce errors and inconsistencies, all systems should still be tested, to some degree, depending on complexity, against the sequence of operation (or ASHRAE 36 standard) to verify all is working properly. As this standard gets introduced into the industry and begins to gain acceptance, keep an open mind to what it can provide but also be leery that it is going to be a ‘set it and forget it’ installation especially as more complex equipment and systems get adopted. Just remember, it is always a lot more difficult going in after the fact to fix a ‘bug’ in the system, so it is best to prove out the sequences prior to project closeout to verify all systems will work in harmony and there are no issues going forward.