Exploring complex hotels, resorts, and casinos: HVAC
Brant Dillon, Director of MEP, Mortenson Construction, Minneapolis
Matt Dolan, PE, LEED AP, Senior Design Engineer, Southland Industries, Las Vegas
Jeffrey S. Grove, PE, Director, JENSEN HUGHES, Las Vegas
Ronald R. Regan, PE, Principal, Triad Consulting Engineers Inc., Morris Plains, N.J.
Mark Richter, PE, LEED AP, Partner, National Residential & Hospitality Practice Leader, AKF Group LLC, New York City
Gregory K Shino, PE, Technical Director of Fire Protection Engineering, NV5, Las Vegas
Toby White, PE, LEED AP, Associate, Sr. Fire Engineer, Arup, Boston
CSE: What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Dolan: We use a few: AHU energy recovery (heat wheels, air-to-air plate heat exchangers), ionization systems for air cleaning within the airstream and space, pool dehumidification systems, chemical water treatment and storage, and underfloor air systems for casino and theater spaces.
Regan: One of our more challenging projects was a resort that wanted to convert a wine cellar into a spa and swimming pool area. The ceiling plenum was very limited and quite inadequate for heating the proposed spaces with air systems alone. We used a high-pressure air-distribution system with variable air volume (VAV) terminals for cooling and designed radiant-floor heating zones for heating that coincided with intended space usage. The spa areas had their own radiant-heat section with dedicated controls, and the swimming pool/locker area received their own zones with heating controls. Although the radiant-floor heating technology is not unusual, it is seen more in residential applications. The novelty of this project was the combination of residential and commercial technologies that resulted in a cozy and comfortable environment for resort guests.
CSE: What types of air economizers or other strategies are owners and facility managers requesting in hotels, resorts, or casinos?
Regan: There are several technologies that we frequently use to increase the energy efficiency of HVAC systems serving hotels and casinos. The air economizers used are dictated by the commercial building codes in most of the continental U.S., and they are ever-present in the modern designs. Other technologies involve energy-recovery wheels, heat exchangers and heat-pipe heat exchangers, and closed-circulating-loop technologies. All these technologies are implemented to extract the heating or cooling energy from the exhaust airstream leaving the building and recirculating this energy into the incoming ventilation airstream. We apply these technologies for casino halls, hotel lobbies and common areas at resorts. In short, all areas occupied by large numbers of people that require high ventilation rates.
Dolan: Airside economizers can be used for extended periods in Las Vegas, due to the dry outdoor-air conditions and cooler shoulder months. Of the types available, the most effective is the enthalpy economizer, which allows it to be used even at dry-bulb temperatures above the return-air temperature due to the lower enthalpy in the dry outdoor air. Even though the outdoor-air dry-bulb temperature is greater than the space/return-air temperature entering the AHU, this air can have a lower enthalpy, thereby requiring less energy to cool down to the design leaving-air temperature.
In areas with high humidity, such as Macau, airside economizer use is limited to low outdoor-air temperatures and has been omitted from some large projects altogether. The outdoor air is often 70% to 90% relative humidity. At these values, the dry-bulb temperature must be depressed below the return-air dry-bulb temperature to maintain the most efficient energy condition at the AHU. This is because the design space conditions typically found in Macau are 73°F dry-bulb (FDB), 55% relative humidity (RH), and 29.96 Btu/lb enthalpy at sea level. The outdoor air at the same dry-bulb temperature will typically have a higher relative humidity and results in an increased enthalpy (73° FDB/80% RH/32.81 Btu/lb). In this installation, the enthalpy economizer is necessary not to extend the range of use, but to limit the energy cost of cooling the outdoor airstream. In addition to airside economizer use at the AHU, a waterside economizer is typically required for most casino projects to precool the chilled water through a heat exchanger and condenser-water loop. This system takes advantage of pre/free cooling of the chilled water when the cooling tower water is driven below the return chilled-water temperature. This system is advantageous for Las Vegas, as well, with the low humidity, thereby low wet-bulb temperatures, that allow open-circuit cooling towers to deliver colder condenser-water temperatures back to the chillers and heat exchangers.
CSE: What types of air balancing do you include in your design? Describe the project.
Dolan: Standard air balancing is used for these projects, including manual or remote-type volume dampers at diffusers, VAV box damper and flow-measurement balancing, and constant-volume and variable-volume exhaust and supply systems (including demand-control ventilation and exhaust for kitchens and constant-volume mechanical ventilation and bathroom exhaust for towers). Smoke control and stair-pressurization balancing using a variable frequency drive (VFD) has become standard practice for these projects. Though the fans are operated at constant volume, the exact airflow rate required to maintain the IBC pressure differentials (0.05 to 0.1 in. wc) must be determined after the building is constructed. This is because the actual building leakage rate may differ from the calculated leakage rates indicated as 2012 IBC maximums in Section 909.5 and as NFPA 92: Standard on Smoke Control Systems values for tight, average, and loose construction in Table A.126.96.36.199. In the past, belt-drive fans were used in all smoke control and stair-pressurization systems to allow for changes in pulleys to decrease or increase fan speeds to meet the life safety requirements. As VFDs have become more reliable and increasingly allowed on life safety fans, we have used them as the standard to ease testing and commissioning at the end of the project.
Regan: There are two types of air-balancing inspection types that we typically specify for our hotel projects: the Associated Air Balance Council (AABC) certified balancing and the comfort air balancing. The initial air balancing is performed by an AABC-certified or National Environmental Balancing Bureau-certified company and aims for the most energy-efficient adjustment of the HVAC system. The result is a highly energy-efficient system that performs well under the heating and cooling design conditions scenarios. However, the design scenarios typically cover extreme weather conditions like cold arctic-winter temperatures or tropical heat waves. These extreme conditions, however, are usually infrequent although highly noticeable by the hotels and resorts clientele. The day-to-day weather conditions are not as extreme. For this reason, our company requests a follow-up air-balancing inspection, usually after 6 months to 1 year of operation, to adjust the system for better comfort of occupants. From our experience, we’ve found that an AABC air-balancing inspection followed by a comfort air-balancing inspection yield a comfortable yet energy-efficient and reliable HVAC system adjustment that satisfies even the most demanding guests.
CSE: What are some common HVAC challenges when you’re met with certain wants/needs from the building owner while on a budget?
Regan: The most common challenge we encounter in our hotel and resort projects is the substantially limited space to disguise the HVAC systems. There never seems to be adequate plenum space for quiet supply-air ductwork. The air conditioning units are frequently landed right next to the sleeping areas and are difficult to silence. Fortunately, the newest HVAC equipment is available with electrically commutated motors (ECM) and digital compressors that operate much more quietly and more efficiently than the older technologies. In most cases, the increased purchase costs of the ECM equipment are more than compensated for by the cost savings on the silencing technologies and the operating costs.
CSE: When integrating the HVAC system with other systems (fire/life safety, lighting, etc.), what are some of the challenges and solutions with integration and interoperability?
Dolan: Determining which systems must be directly wired back to the fire alarm system and which can be accomplished through signals from the building management system (BMS). For active smoke control systems (IBC Section 909), they must be directly wired to the fire alarm system for control/monitoring, but for post-fire salvage systems (IBC 403), the control signals can be completed by the BMS with a programming signal sent by the fire command center. This signal will override all other operations and place the associated units into post-fire salvage operation to provide the required four air changes per hour of exhaust and make-up air. This reduces the complexity of the fire alarm system and quantity of addressable modules necessary to achieve the code requirements.