Many older buildings - some from the 19th century - can be considered crown jewels among the many facilities still in use around the country. Although the outward appearance of many of these jewels is protected and remains relatively unchanged over the span of their long lives, the interiors often experience many alterations as the needs of occupants changed over the years, and as modern infrastructure was developed and incorporated. Even more contemporary systems, particularly communications and HVAC, have gone through their own upgrades.

Any revered architectural icon and registered historic building will require special handling during the process of designing for and implementing a renovation/modernization plan. Over the years, our firm has participated with many design and construction teams in tackling these sensitive projects. Quite often, most often, actually, these older and intrinsically valuable remnants of a more gilded age are still in active use. Remodeling, thus, has to proceed with that added caveat, that whatever you plan for, it has to take into consideration that this is not an ordinary construction project.

Usually, to avoid wholesale disruption of vital office functions during the demolition/re-fitting process, a project will be completed in phases. Consequently, demolition and construction will likely occur in areas adjacent to occupied space. Here is where things can - and usually do - get tricky. In some historic structures, not only must vital services be maintained to adjacent, occupied spaces, but there may well be a compelling need to maintain a certain level of infrastructure to the unoccupied area being worked on. One cannot rip out outdated wiring and ductwork without shutting down the associated systems. Sometimes, too, the system serving the construction zone also serves space still occupied. What’s the plan? How do you go about satisfying these diverse and conflicting needs?

In one case in point, construction in one zone of a particular building forced the temporary relocation of key HVAC equipment. This equipment fed areas in both occupied as well as construction zone space. Further, as with nearly any office building, there were critical function rooms in both areas that could not suffer downtime, and had to be continually conditioned to maintain their unimpeded operational status.

This is expected. If rooms are not being moved or upgraded as part of the major renovation and have to stay in place, and continue to operate normally for the office’s particular requirements, then switch them. Not necessarily expected, though, are historically irreplaceable architectural elements and finishes in the reconstruction zone that will also need continued conditioned air for their preservation. So, now we have an idea of the problem. From an HVAC perspective, service had to be interrupted so construction could proceed. However, the contractor could not cut comfort service to occupied zones, had to maintain a minimum level of service to a select number of switch and other electronic closets, and had to sustain acceptable temperature and humidity levels inside portions of the construction zone to preserve architecturally significant finishes. What to do?

Figure 1. Relocate the dry cooler to be out of the way of construction and yet continue to service critical systems.

It's All About Planning

In design, an engineer must ask a number of questions before offering a solution that meets the owner’s needs and requirements. Loss of service, planned or not, is always a possibility. The question becomes how does the owner want to deal with that possibility? What is and isn’t acceptable? The shorter the outage the better, in any event. But for some owners, no outage is acceptable. This is a reality for many projects, and “in spades” for the project described above.

To reach the best solution, the engineering approach looks at options drawn from: analysis, design, back up solutions, and, temporary solutions, determined by a facility’s existing conditions. Final approaches will be tailored to the owner’s and the facility’s specific needs. The engineer and contractor will ascertain from the owner which system sections are critical. Part of the analysis process will reveal whether any area served by the system can tolerate even a brief shut down during cut-over to temporary service.

In planning for unique temporary needs, preserving historically significant architectural elements such as friezes and other moldings, gilding, wall art, and other detailing, in this case, was a major consideration, along with maintaining vital conditioning to electronic equipment rooms, and maintaining comfort service to occupied areas.

In addition to maintaining service to designated areas, part of the analysis included consideration of ambient air conditions in adjacent construction areas. Demolition in adjacent served spaces would create dust and other uncontrollable air quality debris problems. In supplying temporary HVAC, locating temporary support piping, wiring, and equipment is another vital part of the decision making process. The design solution had to account for sufficient physical access - getting temporary equipment into the areas needing it, power availability, and whether the support infrastructure creates conflict with the owner’s goal of preserving critical existing architectural or historic features, and also if it interferes with restoration/modernization construction activity.

When shutting down an existing system, design engineers recognize that a temporary system cannot adversely affect fire/life safety, industrial or process cooling and ventilation, freeze protection, and flood prevention systems. From this perspective, the case project, typical of many major office buildings, primarily concentrated on spaces within the construction zone that needed continuous service, namely those spaces dedicated to communication, computer servers, as well as the portions containing historically significant rooms and passages. Further, occupied areas outside the construction zone needed ongoing HVAC service. When planning ahead, depending on the critical nature of the building system and with the owner’s acknowledgement and funding, the designer should include, in the central system, a means to provide temporary backup capacity. These are listed in Table 1.

Table 1. Recommended concepts for engineers designing for new critical system installations.

A Balancing Act

Some systems affected by the construction served both occupied and renovated areas, which added to the project’s complexity. The loads for the two areas were unbalanced, yet both required continued service.

When planning a shut down of normal service, designers should consider shifting terminal, communications and/or computer interfaces to a different location if possible. At the case study structure, a relocation strategy was implemented by first reducing the load serving one occupied area, and re-routing conditioned air from another system to take up the shortfall in the designated space. This strategy allowed the owner to economize by avoiding renting or securing outside temporary equipment. The switch over to the temporary system was also timed to take place at the building’s lowest point of system demand and occupancy - a weekend - to minimize discomfort and inconvenience.

As the renovation and upgrading progressed in phases, most of the first renovated phase was adapted to accommodate a new four-pipe fancoil unit system serviced by a central chiller and heating plant. While removing most of the old mechanical piping and electrical wiring, a number of rooms needed to remain operational with full conditioning service during construction.

Part of the construction plan was to work around these areas without interfering with their operation, and to contain construction dust so it wouldn’t intrude into the operating spaces. To preserve the building’s historical architecture, chases were cut into the walls for the modernization, MEP risers were installed, and then the walls refinished so that the new HVAC ducts and vents were nearly invisible, leaving the “new” space matching the original construction concepts.

Part of the current renovation/construction process called for relocating an existing air cooled chiller and dry cooler, yet the fancoil units and computer room air conditioner (CRAC) units they served stayed in place and had to maintain operations.

Making The Most Of Minimal Disruption

The D-B team’s mechanical contractor developed a solution to eliminate downtime during the switch over. Piping connections were installed before the equipment was to be relocated. This minimized downtime disruption to other occupied building operations. This would be nearly the identical procedure if the contractor were to rent temporary equipment.

Besides adding new piping and shutoff valve connections at the new locations, the mechanical contractor installed an additional domestic water connection and a back-flow preventer. After installing new power connections, the contractor was ready to reconnect the existing 80-ton chiller and two 25-ton dry coolers moved from the courtyard (Figure 1).

When all was prepared, on the first available weekend, during minimum facility occupancy, the mechanical contractor tapped and connected the domestic water line, supplying temperatures below 76°F, for a once-through application. This was enough to support an accepted level of cooling to spaces requiring conditioning during the cut over. The contractor then reconnected the chillers and dry coolers to the fancoil units and CRAC units that same Saturday. The owner did not notice a difference in operation. Using domestic water as a “cooling” source and as a “condensor” source for the critical spaces was a valuable contribution from a subcontractor, working closely with the designer and general contractor.

For the historical areas under restoration and needing continued conditioning, the D-B contractor isolated those areas from intrusion of dust/debris from other sources with a series of screen baffles and rented an area spot cooler, ducting the discharge condenser air out a window. This proved to be a relatively simple, inexpensive, yet effective, approach.

As noted, some solutions that made the entire process of maintaining conditioning to critical areas during a temporary shut down of the permanent HVAC system originated with the mechanical contractor, in conjunction with the design engineers and general contractor. Throughout the delivery process, in the D-B environment, meeting challenges is everyone’s job. When working well, D-B is a true “team” approach to project delivery that goes a long way toward ensuring all stakeholders take real ownership in the project, including the client.