Andy McGreevy shows off his invention for turning unused hot water from the a/c system into a useable source for the entire Grand Hotel hot water system.

MACKINAC ISLAND, Mich. - Picture the look on the face of a business owner when an HVAC contractor tells him that the more he uses his air conditioner, the lower his electric bill will be. Besides astonishment, the business owner may be calling for the men in white jackets to take the contractor away.

Yet that scenario may soon play out in businesses across North America if Andy McGreevy and his newest invention are made the air conditioning system of choice.

McGreevy, owner of Petoskey Commercial Equipment in Petoskey, Mich., and maintenance engineer-consultant for the world famous Grand Hotel on Mackinac Island, recently installed his Double-Duty air conditioning systems in 188 of the hotel’s guest rooms. It completes a lengthy project of ensuring that each guest enjoys cool comfort during his or her stay at the 120-year-old landmark.

The hotel is open from May to October and has been the setting for many high-level political and entertainment events. Several Hollywood movies have been shot at the Grand Hotel, including This Time for Keeps with Esther Williams and Jimmy Durante and Somewhere in Time with Christopher Reeve and Jane Seymour. It has endured many changes, yet retained its traditional ambience. After 6 p.m., men are still required to be attired in jackets and ties and women are asked to wear dresses.

Each guest room is individually decorated, with most facing Lake Huron and overlooking magnificently kept lawns and gardens, as well as overlooking the historic village on Mackinac Island, which is located between Michigan’s Upper and Lower Peninsulas.

While the Grand Hotel has hosted many famous celebrities, it remained loyal to its past by not disturbing the building envelope with updated mechanical equipment, namely air conditioning systems. Guests had to be content with being cooled from sea breezes, although not sufficient to cool them down during hot summer months.

“Front rooms were getting up to 90°F and there had been lots of complaints,” said McGreevy. “In fact, some people would call the front desk and complain that their air conditioning wasn’t working and were told that there was no air conditioning.”

Hotel operators had balked at the idea of adding window air conditioning units or vented PTAC units, which would have changed the look of the hotel.

The guest rooms on the non-water side in the rear of the hotel are out of view from tourists and guests - and slight alterations to their look were deemed acceptable. So the hotel installed PTAC units, custom fitted by manufacturer Ice Cap. The units below each room’s picture window were vented to the outside through grilles, which blended into the building’s exterior, yet still altered the look. Hotel operators did not want the same look on the famous exterior facing Lake Huron.

The air handling unit with evaporator coil is mounted on a common wall shared by the bathroom, where the water-cooled condensing unit is located under the bathroom sink.

McGreevy thought he knew the solution. He has been a member of the Grand Hotel maintenance staff since 1984. A native of Mackinac Island, McGreevy has an electronics degree and a great deal of experience in refrigeration, which he learned from his late father, James, the former head of maintenance for the Grand Hotel.

“The longer I worked at the hotel, the more I got into engineering and design,” he said.

He discussed several options with hotel operators such as chilled-water systems, but that would mean tearing through walls to install piping, something that might damage the structure and prove to be very costly in wall repairs. “It’s hard to find two walls that line up from floor to floor,” McGreevy said. “Running pipe would be very expensive and almost physically impossible.”

Installing a split system would also require more piping and would require rooftop units, which would negatively impact the look of the hotel.

The rooms in the rear of the Grand Hotel are serviced by individual PTAC units such as this. Each unit is vented to the outside and the vents do not impact the exterior ‘look’ of the building since the rear is hidden from most views.


McGreevy came up with an idea that would utilize each room’s cold-water supply and turn it into water for the a/c system, as well as excess heated water for the hotel’s hot-water system. He said a heat exchanger tied into the cold-water supply and the hot water supply would provide an efficient way to cool each room and add a new source of hot water for the hotel, while conserving energy and lowering the hotel’s utility bills.

Needless to say, hotel operators were intrigued with the idea.

In order to set the stage for the explanation, it is important to point out that the energy sources on Mackinac Island are electricity and propane gas. There is no natural gas available. Electric boilers heat the Grand Hotel’s hot water tanks.

McGreevy’s under-the-sink condensing unit involves using cold water, which would normally run down the drain, to be supplied to a flat plate double-wall heat exchanger. The double-wall heat exchanger is used to transfer the heat from the air conditioning refrigeration circuit to the hotel’s potable water system. Heated water from the heat exchange system is piped back into the hotel’s hot water supply rather than being dumped down the drain. “Essentially you have a water-cooled condensing unit that is not consuming any water,” McGreevy said. “The units, in turn, heat the water at one-third of the cost of normally heating our hot water tanks, acting as an air-source heat pump.

“I did a lot of research and couldn’t find a manufacturer who made a system like this.” So, with the help of his father-in-law Marty Warren, McGreevy designed the entire system and showed the Grand Hotel operators how it could actually save them money.

The system feeds hot water into the hotel’s main hot water supply when there is a call for air conditioning. There is less of a demand for using the electric boilers to provide heat for hot water, thus lowering the cost of electricity to run the boilers. McGreevy said that when the demand for air conditioning is so great, the boilers actually shut down.

If that demand becomes so great - as it does on a regular basis - a programmable controller sends a signal to a bleed valve and the water is dumped in the hotel’s outdoor swimming pool.

Andy McGreevy stands in front of one of the Grand Hotel’s three hot water heaters, which receive hot water from each individual room’s a/c system, which he invented.

“It’s a 60-year-old concrete pool and it leaks,” said McGreevy. “One inch of water loss equals 5,000 gallons of water. Instead of running cold water to the pool where it is heated, we are running heated water to the pool which comes from the air conditioning system.”

If, by chance, there is still enough water left over, McGreevy has tied a line into the hotel’s irrigation system to handle the overflow. He hasn’t had to use the water to irrigate the lawn - yet.

Excess water sent to the pool is metered and deducted from the Mackinac Island Sewer Department’s monthly bill.

So to recap, the Double-Duty air conditioning-hot water system is lowering the Grand Hotel’s electric bill and not increasing the water and sewer bills. It’s no wonder that other hotels on the island are asking McGreevy to install the same system in their guest rooms.

“I have a lot of inquiries about the system,” he said. “There are probably a lot of old brick buildings that could use these units.” He has had so many inquiries that McGreevy has applied for a patent for the system, which, besides Flat Plate heat exchangers, includes Bell & Gossett pumps and First Company fan coils. He hopes to market it soon.

And one more cost-saving advantage: installation is quick and easy. McGreevy used various members of the Grand Hotel’s 10-person maintenance staff to do the work. “I can have a two-person crew [each person has a mechanical license] install three of these systems each day,” he said. ‘It is basically like installing a mini-split system.

“This installation saves on the cost of running pipe. A plumber would have to work all winter to run lines, followed by a carpenter and patching/painting crew. That isn’t necessary with this system.

“It is a win-win situation.”

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Publication date:08/06/2007