DUBLIN, OH—When the AC Hotel Columbus Dublin was being built here in 2016, guest comfort and energy efficiency were of the utmost importance.
In order to meet those needs when it came to the HVAC system, the developer, Crawford Hoying LLC, was initially looking to install a load-matching water-source heat pump (WSHP) system for the 104,250-sq.-ft., eight-story hotel.
Instead, Mike Machemehl, commercial sales manager with Mitsubishi Electric, suggested a solution from his company. “I knew the developer and was aware of the project,” he said. “WSHP systems are fairly energy efficient, but not as much as a VRF (variable refrigerant flow) system. Knowing our technology would be a good match for the hotel, I told the developer I could save them about $100,000 annually through combined utilities and maintenance savings.”
Switching to VRF ultimately proved to be more cost effective even before accounting for maintenance and utilities savings. When the contracting team from Brackett Builders priced out the installation, the total installed mechanical costs came out to $550,000 less than the WSHP system.
Between a WSHP system and water-source VRF, the biggest difference in price and efficiency comes down to the number of compressors and water pumps required for the project, according to the company.
“In the initial design with WSHPs, there’s a compressor bearing unit in every hotel room, plus more for the common areas,” said Machemehl. “For each of the WSHP units, a fractional, horsepower water pump is built into the heat pump cabinet.”
With the more efficient water-source VRF systems, the total tonnage was reduced due to increased system diversity. In addition, the number of compressors was reduced from 182 down to 19 and the total count of water pumps was reduced from 190 to five.
Paring down the number of systems also proved to be imperative for a high-class guest experience. “The AC Marriott brand, founded by Antonio Catalan, is a lifestyle brand focused on sophistication, service and design,” said GM Orcun Turkay of the Shaner Hotel Group. “The most important thing for our hotel guests is that HVAC operation is simple, comfortable and unnoticed. Guest comfort is a huge component when it comes to our industry.”
For Turkay, the biggest thing you notice with the VRF system is how quiet it is in the guestrooms. “Rather than every room having its own individual compressor in each unit, it feeds from a central one, thus reducing the noise level in the guestrooms,” he said. “It also gives our building the ability to run heating or cooling in different zones through a single refrigerant piping system based on what the guest desires.”
Within the AC Hotel Columbus Dublin, compressors are located in the housekeeping rooms rather than guestrooms. “We’re seeing a pretty big shift in the hospitality vertical market toward VRF,” explained Machemehl. “The big reasons: energy efficiency through heat recovery, maintenance, comfort and acoustics. When I stay at a hotel and I can hear the compressor kick on, it wakes me up in the middle of the night. The result of the VRF system is a better experience for guests and much better comfort from a temperature and humidity control standpoint. Unlike traditional systems where the compressor constantly turns off and on, a VRF system always has the compressor running and adjusts the fan speed to continuously remove moisture.”
Utilizing water-source VRF also has its advantages in handling extreme temperatures, according to the company. Central Ohio winters can be harsh, with temperatures occasionally dipping below zero. “With traditional HVAC systems, extreme cold can cause a loss in capacity and efficiency, ultimately impacting the hotel’s ability to provide optimal heating,” he said. “With water-source VRF, the system doesn’t struggle to accommodate temperatures below design as it strategically uses a combination of recovered heat and a natural gas boiler-heated water loop.”
The hotel staff experienced the effectiveness of this design firsthand last winter. “In January 2018, there was a six-degree day—extremely cold,” said Machemehl. “Though it was sunny with a high solar load on the building, I wanted to go out to the hotel to make sure the building was operating correctly. Basically, this system operates off the principle of heat recovery, so the VRF system will capture all of the waste heat in the building—lights, people, projectors and kitchen equipment—in addition to the solar gain on the building. When I checked the controls, not one of the boilers was running… From an energy-savings and sustainability standpoint, that’s a homerun to have your boilers off when it’s six degrees above zero outside.”
In addition to helping to provide guests with greater comfort, the system’s high-performance efficiencies allowed Crawford Hoying and systems engineer, Prater Engineering Associates, to receive substantial rebates.
A third-party energy-modeling program was used to do a projection of energy usage with the local utility company American Electric Power (AEP). The custom rebate program compares how much better the building’s projected performance is compared to a baseline ASHRAE 90.1 building. AEP pays 10 cents for the estimated first year’s kilowatt hour (kWh) and three cents per kWh to the designer. In this instance, Crawford Hoying received $44,900 and Prater Engineering received $13,500.
“The sophistication of this system is so different from others I’ve used,” said Turkay. “With the nature of our building being all glass, energy efficiency is so important in our operations. We haven’t had any issues with the system and, at the end of the day, our guests are happy.” HB