Where Comfort Is Stressed (October 1999)
When it came time to design a new hvac system for the guest rooms and other facilities, comfort and aesthetics were clearly the family's top concerns. This agenda differed somewhat from an ordinary commercial project's priorities, and the owner's wishes gave the project a different array of problems and rewards.
Exceptional Comfort, Unusual ChallengesTypically, the initial hvac cost per room is estimated in a ±20% budget form. This allows a basic idea of material purchase requirements, ease of maintenance, ease of replacement or repair, and predicted operating costs. These values are used to create a cost analysis that drives the subsequent hvac design. In the case of the Bavarian Inn Lodge, a series of design constraints required diligent attention to detail as the process' mechanical elements were coordinated with other trades. The following list represents only a portion of the complete complement of qualifications.
- Rooms may not have any forced-air equipment within the space.
- Humidity control for the living space was required.
- Fresh air and exhaust were to be of separate systems for possible low-temp heat recovery.
- Equipment noise was to be dampened, if not totally eliminated.
- Filter replacement was to be centralized.
- Hvac controls were to include automation to match the occupancy cycles of each room.
- Final acceptance of temperature controls was dependent on working, commissioned examples by room.
The 6-in. metal stud walls with bat-and-drybit envelope construction made electrical energy the preferred main heating source instead of gas. This, in turn, led to the elimination of the perimeter heating system, and the installation of an individual electrical duct coil in each room to control humidity.
While electricity served the primary heating needs, natural gas was still used to heat potable water.
Incentives from the electric utility added to the allure of this system. A handsome reduction in demand charges was offered, offsetting any energy savings the owner would have realized from using alternative natural gas heating sources. This somewhat atypical effort by the utility to sponsor the conceptual energy design meant that the hvac designer didn't have to spend time providing cost justification modeling for alternative designs.
A water-source heat pump was chosen as the heating and cooling device to match existing manufactured equipment. However, to satisfy the constraints pertaining to noise, humidity control, and localized forced air, the decision was made to add a sixth floor to the structure. This area, consisting of metal stud and joist, serves simply to house the mechanical equipment. The floor (or, more accurately, attic) became the mechanical penthouse. Its design layout was unlike any known before.
To achieve vibration isolation, a floating floor was installed under major equipment pads. Each of the two centralized makeup air systems were precooled and preheated by air handling units with low-temperature heat exchanger preheat and dehumidifying coils.
Centralized exhaust was pulled through a separate bath ventilation system in each room. This allowed every bathroom to have negative pressure with respect to the other living space. This method - requiring 25% exhaust airflow, preconditioning the makeup airstream - was the most effective way to control moisture within the living space.
Reheat control was achieved by a small electrical heating coil, duct-mounted downstream of the heat pump, then positioned at the horizontal supply duct entrance to each room via the corridor.
The heat pump electrical service monitors the energy use of the coil. This special design was provided by the heat pump manufacturer to minimize electrical circuitry.
Humidity Under The Big TopThe guest rooms were only part of the Bavarian Inn Lodge hvac puzzle. The newest piece of the complex is an expansive Fun Center. The attractions in this area include an 18-hole miniature golf course, swimming pool, cafeteria-style restaurant, bar, and video arcade areas.
A large amphitheater-type space houses both the miniature golf and pool and video areas. The hvac design of these adjacent spaces would normally require envelope separation, but installing an underfloor duct air curtain minimized humidity transfer from the pool to the golf area.
A Dectron dehumidifier was installed to condition the majority of the pool space, with half of its air split off and conditioned with a reheat coil that uses recirculated pool water. A supply duct was placed under the slab for the space, and a return duct was positioned so that the major air migration was from the golf course to the pool.
This basically sweeps the humidity from the surface of the pool. The dehumidified air is then used to ventilate the golf course area and supplement winter heating for the course's massive floor space.
The pool is kept at the proper temperature to bring the discharge air, which moves to the golf area, at a comfortable level for putting, as well as to keep the pool area at negative pressure to minimize migration of humidity. Although this design was effective, the high, vaulted ceilings and subsequent humidity on the skylights required destratification fans.
These fans served their purpose, but they also disrupted the air curtain effect. In hindsight, one might suspect that it may have been more economical to use spiral, exposed ductwork for distribution in the large, open space. It may have been, but the owner would not conceive of it, insisting on keeping such equipment out of sight.
The total cost of the facility is not public information, but it is likely that the ultimate hvac design was more than three times as expensive as a standard design. After two years of construction, the Fun Center complex was finished and occupied in late 1994.
Filled To 2000The most interesting experience of the project involved the total quality management (TQM) partnering method employed by the designers, construction manager, and owner.
In lieu of a typical routine of addenda, bulletins, and changeorders, a more cost-effective, streamlined process was employed. Trade foremen were involved in the field changeorder discussion at partnering meetings, where changeorders were then issued after considering cost management, timelines, and trade organization factors.
This cross-pollination of ideas helped the design-build process, leading to a better-managed construction project for the owner. Partnering also provided the owner with the financial insight to allow for contingencies in the process, ensuring that design requirements drove cost, not vice versa.
If the overall process can be judged by the popularity of the finished product, then the project was quite successful indeed. At this point, the hotel has reservations that stretch into the year 2000, and the Zehnder family is planning further expansion for the Bavarian complex. ES