Building Controls Exist Outside of a BAS
Don’t forget about the so-called simple controls that can create complications down the road.
As demonstrated with manual winterization requirements last month (Winterization and Commissioning, January 2019), systems manuals should include more than a regurgitation of the BAS as-built documents. Not everything in a project is necessarily controlled by the BAS, and, believe it or not, some buildings are still constructed with no central BAS at all.
Whereas very simple electric controls, such as thermostats for furnaces, fan-coil units, or heat pumps, can be self-explanatory, there are often more complex — but still stand-alone — controllers installed in non-BAS facilities. These can be little black boxes set up by the installation contractor, which, theoretically, require no user interface from the building operator and/or occupants. Any adjustment or troubleshooting will need to be performed by a service contractor with customized (proprietary?) tools.
In other cases, the controllers will have a limited user interface that requires documentation and training regarding when and how the building operator needs to manipulate them.
In either case, these controllers are not necessarily intuitive and the only place their custom application details, i.e. specific to a particular system, may be documented is in the systems manual. The following are some examples of this.
Dual Temperature Distribution Pumps Summer/Winter Switchover
For energy conservation purposes, some dual-temperature (heating hot water in the winter and chilled water in the summer) systems utilize a single set of pumps for both summer and winter operation. Winter operation often requires less total flow than summer operation. As such, some pump speed controllers will have a manual summer/winter switchover feature to change the pump speed based on time of year.
The systems manual needs to explain this operating strategy and provide step-by-step instructions on how to make the seasonal switch each spring and fall.
Variable Primary Flow Chilled Water System
A primary pumped, variable-speed chilled water system needs a mechanism to ensure the flow through the chiller never drops below the manufacturer’s recommended minimum flow rate. A common simple system might include a bypass valve that would allow chilled water supply to flow directly back to the chiller (bypass the distribution system) when the total chilled water demand at the cooling coils is lower than the chiller minimum flow.
This is an absolutely critical operation that is not necessarily obvious to the chilled water system service contractor. Chiller maintenance typically focuses simply on the chiller and not necessarily on the system into which it is integrated.
A chilled water system schematic diagram showing the bypass valve and its controlling device (chiller flow meter or differential pressure sensor) along with a floor plan showing the locations of these critical components needs to be included in the systems manual. This should be accompanied by the set point for bypass valve control (minimum chiller flow or differential pressure) determined by the balancing contractor.
Domestic Hot Water Boiler Controls
For a domestic hot water (DHW) system with boilers or heat exchangers separate from the DHW storage tanks, it’s important to document to what temperature the boilers/heat exchangers are to be controlled. Also, with multiple boilers/heat exchangers, it’s important to document the intended staging sequence.
For example, we retro-commissioned a four-year-old system like this, which had not been commissioned as part of the original construction, and found two DHW boilers each controlling its own leaving water temperature. That hot water was combined downstream of the boilers and piped to two parallel storage tanks. Cold water make-up and recirculation hot water were introduced to the piping upstream of the storage tanks.
During our review of the original design documents, it was clear that the system was intended to maintain a constant temperature set point in the storage tanks, i.e. not a constant boiler leaving water temperature. This was a system that could have benefitted from a systems manual schematic and sequence of operation because the two reputable contractors who had serviced the building over the first four years did not identify the control system anomaly when trying to troubleshoot chronic DHW temperature problems.
It’s tempting to focus commissioning attention on systems controlled and monitored by a BAS, but this should never be at the expense of paying close attention to the systems with stand-alone controllers. The latter may actually be more important for the commissioning professional to understand and document for posterity (i.e. in the systems manual) because customized as-built/as-programmed documentation for those controllers may not be prepared by anyone else on the project team.