In HVAC, hybrids are often defined by the comfort level building occupants strive to achieve. In today's techno world, it is possible to combine equipment into an efficient system that raises the comfort level beyond normal means - and customers are showing a willingness to pay extra for indoor comfort. That comfort level is also accompanied by lower energy costs, making hybrid systems an attractive option for building and homeowners.

But hybrid systems are not a cure-all for everyone. Depending on the application and design of the system, achieving maximum comfort can be a pie-in-the-sky objective. And like hybrid automobiles, there is often a higher cost associated with initial installations.

Designing a hybrid system can be both rewarding and challenging, as no two building occupants have the same comfort levels. Glen Stanton, training manager for Burnham Hydronics, knows that from personal experience.

"Above and beyond everything else should be consideration in providing for the various and often differing comfort levels of the individuals that occupy the home or building," he said. "There will undoubtedly be varying requirements for different temperatures or comfort levels based on each person's preferences.

"For example, in my own bedroom, in the spring and fall when heating requirements are quite moderate, I find myself sleeping on top of the covers while my wife is buried away under a blanket with a flannel nightgown as well! These personal preferences can vary among each family member or building occupant.

"The same always tends to occur in an office building type environment where you will find some occupants running their air conditioning while their secretary has an electric space heater glowing under the desk in an effort to stay warm."

Pros And Cons Of Hybrid Systems

"By this I mean that a single or modular boiler application can easily provide the necessary Btu's to maintain hydro air zones, baseboard or radiator zones, radiant heat zones, indirect hot water needs, as well as other loads such as pool or spa heating and snow melting," he said. "One of the better benefits involves using multiple remotely mounted air handlers to provide numerous comfort levels of heating and cooling throughout the building."

D. Michael Smith, senior marketing director for Mitsubishi Electric HVAC, believes that because a hybrid system can consist of different types of ventilation and heating/cooling solutions, the pros and cons will vary widely. And he added, "The idea of hybrid systems (as a single-source solution) does not jive with what the consumer wants and the concept is confusing. Typically, customers choose hydronics for the energy savings and the ability to provide draft-free silent heating, plus the added benefit of space savings since large-scale ducting is not needed."

Stanton said one con of hybrid systems is in the design itself. If a system is not designed and sized correctly, the results can often have a negative effect.

"One con involves a contractor oversizing a single or modular boiler system to guarantee enough Btu's to satisfy the whole demand load of all the hybrid components all of the time," Stanton said. "There are integrated devices to allow just enough heat to be generated to satisfy all of the loads based on how and when they are being used. For example, with the space heating load of 150,000 Btuh, indirect hot water load of 130,000 Btuh, and pool-heating load of 150,000 Btuh, would the contractor size the boiler(s) for 430,000 Btuh of capacity?"

Mitsubishi Electric HVAC’s Mr. Slim®, a split-ductless cooling and heating system, provided Paul Hamel, owner and president of Iceberg Mechanical, Brooklyn, N.Y., Staten Island, N.Y. with a solution to his own home’s cooling problems. Hamel had already installed radiant floor heating (above) and chose Mr. Slim as the home’s cooling solution.

Hybrid Systems & IAQ

"The issues of fresh air and IAQ have not become top-of-mind with most consumers except in northern markets like Minnesota and Wisconsin, where homes are closed up for so long during the heating season and those states require ventilation in residential home construction," he said. "The majority of the U.S. markets will be primarily concerned with the heating and cooling aspects of a system."

Stanton tells a story about how the IAQ issue arose during the construction of a home in Rhode Island. "This house was built into the side of a hill sloping down to the river and the design did not include a basement," he said.

"When I first met the homeowner, much of the house was framed and the lower-level floors were already poured. He inquired about the possibility of radiant floor heating in this new dream house.

"The contractor installed the radiant tubing in the entire first level and with zones for the [various rooms]. We made the ‘great room' the controlling factor for the system by equipping it with a room sensor that provided feedback to a weather-responsive control to constantly modulate water temperature to the great room zone and always keep it flowing provided the outdoor temperature was below 75 degrees F. The rest of the zones were operated by room thermostats and were a slave to the modulated water temperature the great room was establishing.

"The end result was a system that could operate on greatly reduced water temperature and provide maximum comfort with little or no temperature deviation. The radiant effect of the large floor surface of the great room would allow temperatures to rise evenly to a stratification level about 7 to 8 feet off of the floor. That level would always stay in place by the upper level cooler air dropping and the floor temperature rising. The end result is that he was effectively only heating one-third of the volume of the room or the lower level where he was living.

"Overall [the owner's] satisfaction involved the fact that he was totally unaware of any weather changes outside the house due to the dead constant room temperatures he experienced inside the house. In this aspect, our mission was accomplished in providing excellent comfort levels. His dissatisfaction involved the fact that he preferred to smoke Cuban cigars with his friends from time to time. The problem was that the smoke tended to remain at the stratification level or about 7 to 8 feet off of the great room floor. If anyone happened to enter the front door while this was occurring, the great room would somewhat resemble Los Angeles on a very smoggy day.

"When confronted with this dilemma, I invited his HVAC contractor into the room to discuss the possibilities of installing an air exchange system to recirculate this air at the stratification level and to introduce conditioned fresh air. The system was installed in the kitchen wall adjacent to the garage and the owner is now completely satisfied with his system."

Hamel installed two Mr. Slim MS24WN models on the first floor of his ocean-front beach house — cooling the large free-flowing space.

What The Experts Suggest

Stanton described some of the components that go into the system. "These products include cast iron baseboard, cast iron radiators, radiant floor heating, panel radiators and baseboard, towel warmers, kick space heaters, convectors, unit heaters, air handlers, indirect water heaters and heat exchangers for snow and ice melting, spa or swimming pool heating and other applications," he said.

"These are all presented as a full spectrum that can and does work as an integrated system. In addition to these products, we also market control devices from various manufacturers such as Tekmar, Taco, Honeywell, and Danfoss that help in achieving the desired integration of the system."

Smith prefers the ease of ductless systems as an alternative to hybrids. "Our recommendation is to provide ductless-type zoned cooling," he said.

"For fresh air, you may need a separate system depending on your building. If you have an open floor plan, then you may need minimal ducting to bring a whole-house supply of fresh air, or to the zones most critical. Otherwise, you may employ ductless indoor models that allow for the introduction of a nominal amount of fresh air, plus taking care of the air conditioning.

"Our ceiling-recess cassette models have a fresh-air intake. The beauty of this design is in the ductless nature of the air conditioning along with minimal ducting to the outside for fresh air. Plumbers may be able to perform most of the ductless installation since there is minimal ductwork - just unit mounting and refrigerant line runs, plus minimal electrical. Local regulations will apply. This can add to the economies of the installation."

Are hybrid systems the wave of the future or will consumers continue to buy traditional HVAC equipment recommended by installing contractors? It may just boil down to choice and application. Either way, it is critical to know what the customer wants and design it according to their wishes, hybrid or not.

Publication date: 10/17/2005