- Alex Mathers
Commissioning Core and Shell Projects – Challenges and Solutions
New, ground up developer led projects are typically built as two distinct and separate projects.
There is “Core and Shell” or Base Building Projects where the basic inside (Core) and the outer building envelope (Shell) are constructed and there are “Tenant Improvement” projects (T.I.) where the interior spaces are custom built to tenant requirements.
The Core and Shell
The Shell is the exterior elements which cover the core of commercial buildings and properties. The Shell of a building includes its exterior features such as the structural skeleton, foundation, and the external walls. The Core of a building is its interior elements such as staircases, elevator shafts and pipes. You can consider the core of the building to be anything that connects the other spaces of the building or houses building elements. For example: mechanical devices or wiring and pipes. Hardware essentials such as water pipes, electrical boxes, and even toilets can be considered part of the Core of the building as well.
Core and Shell construction projects can be further defined as “cold shell” or “warm shell.” Cold shell typically means the space does not have HVAC (heating, ventilation, and air conditioning) available or installed in the space; and hence, the space cannot be heated (or cooled) prior to the HVAC being installed. For cold shell projects, an HVAC unit will need to be installed as part of the tenant improvement.
T.I. (tenant improvements or tenant fit out) is the customized alterations a building owner makes to a rental space as part of the lease agreement to configure the space for the needs of that particular tenant. Tenant improvement projects include everything required to complete a working space with walls, ceilings, electrical, plumbing, HVAC, and any other user specific process systems.
For warm shell projects, an HVAC system is connected and functional, or at least is attached to the premises and ready to be hooked up. Warm means the space can be - or is ready to be - heated and cooled. These spaces are sometimes designed with minimum ventilation for construction cost and energy savings, but air handling units (AHU) serving these areas are designed for maximum capacity.
For the sake of this article, we will assume the Shell we are commissioning is a warm shell that includes air handlers and exhaust fans and a chilled water and heating hot water system and controls. Typically, warm shell projects include fully built out common areas such as lobbies, stairwells, elevators, restrooms, and other amenity spaces. The HVAC systems are sized to accommodate future tenant needs.
Testing and Balance
The problem arises with functional testing systems that are installed before they are to be used – or used to their full extent. Usually, when a warm shell is complete, the T.I. is not and may not be for a while (months or even years). The air handlers, exhaust fans, and a chilled water and heating hot water systems are installed but are not connected to anything or are only connected to a partial system. Shafts and mains may be installed but blanked off at each empty floor.
Even before we start our functional testing, the test and balance (TAB) contractor must test, adjust, and balance the HVAC system so that its performance meets the design intent. But how can half of a system be balanced? How can air flow through a non-existent VAV system or water flow through reheat coils that are not there be measured? They can’t and they won’t be.
The Chicken and the Egg
Without a load, or even a termination point, the ability to test, let alone balance a closed loop system is futile. The obvious solution is to wait for the T.I. or fit out to be complete and then test the core and shell systems. But is this testing performed before or after the T.I. systems themselves are tested and balanced? Again, the core and shell systems need a load to verify performance characteristics. Without a balance on the TI side, it is unknown if the load placed on the systems is per design. So, maybe the TI systems are tested and balanced first and then the core systems. But again, to prove the TI distribution systems are working per design, it is necessary to have consistency on the core system generation side.
Warranty Phase Run Out
A further issue is the timing of the tenant improvements. If the core and shell systems are installed and started up, they may be deemed “in service” by the vendor. However, if the equipment has a one-year warranty and the T.I. is not complete until 12 or 18 months later, by the time functional testing can commence, the warranty of the equipment may have run out. By that time, any issues found with the equipment would fall under the responsibility of the owner. Therefore, it is important to understand the contract language as it pertains to handoff timing and warranty period commencement.
This can be true for not just the equipment but also engineering design, controls, piping, sheet metal, and other trades.
Maintenance and Operations
Along the same lines as the warranty are the systems and equipment regularly inspected and maintained. Just because the equipment is not running does not mean it is not deteriorating. If piping has been filled with water, is it regularly circulated or is it sitting stagnate for months?
If all these issues were not enough to make you run for the hills, another wrinkle can come from different teams working in the same building. Typically, the core and shell developers and the building tenants are different owners. Therefore, the teams could have completely different architects, engineers, contractors, TAB, controls, and yes, even commissioning agents.
There is a significant amount of interface required for T.I. systems to work with warm shell systems and which typically causes questions to arise. Who is controlling what? Where are the points of connection? Who is responsible for power, flushing, balancing, setpoints and schedules? These compound when complex and multifaceted issues arise, and so fingers are pointed.
There is no silver bullet. Unless the building core and shell and T.I. is fully constructed at the same time with the same teams, there will be issues. If not, here are some solutions that may help:
1. Factory Testing - If you know that large equipment (chillers, boilers, AHUs) won’t be able to be performance tested until after an extended period, I highly recommend an owner factory witness test (I would recommend this even if there was not a schedule factor). By proving the equipment functionality and performance in the factory prior to shipment any issues can be remedied prior to arriving onsite. It is better to know now than one or two years later.
2. Planned Closed Loop Bypasses – For closed looped, warm shell systems (CHW, HHW, AHU/Exhaust), it is recommended to provide temporary bypasses to allow for full design flow. This has some additional cost as it is not a permanent solution, but it does provide a path for a significant amount of onsite functional testing to be completed prior to T.I. systems installation. Setpoints, alarms, safety shutdowns, and some sequences can be verified if the systems are allowed to run.
3. Planned Load – The full flow bypasses also provide methods for introducing dummy loads onto the systems. The HHW, CHW and CW system for example can be loaded by opening the AHU economizers during a design day (hot or cold) and flowing outside air across the coils.
4. Planned Maintenance – Ensure the equipment is kept in spec with the warranty requirements by performing regular, preventive, maintenance. This is also assisted by full flow bypasses. The ability to run pumps and fans periodically while waiting for TI connections is significant.
5. Coordination – At the end of the day it all comes down to communication and coordination between the teams. Specific meeting should be held between core and shell and TI teams to ensure alignment. Coordination is critical also for TAB. As mentioned before, the core systems and TI systems TAB process must be managed from a higher level.
The concept of shell and core is that the developer's scope of work is the design and construction of the base building. The T.I. is left to be completed before the building is occupied. This delivery model, while effective, presents challenges to the teams designing, constructing, and commissioning the building. These challenges can be addressed early, provided the teams understand what is required to complete their tasks.