When approached by the architect Roc Caivano Architects of Bar Harbor, ME, with the plans to develop a new community and daycare center for a Northeast community, Sutton Engineering Services, Inc., of Damariscotta, ME, was challenged to come up with a highly efficient but cost-effective solution to heating, ventilation and domestic water generation for the 10,000-square-foot “Harbor House” project located in Southwest Harbor, ME. The engineer selected some of the latest technology in the approach to this challenge.

It is common practice in many buildings in this cold Northeastern coastal environment to use some form of hydronic heat with oil-fired cast iron boilers and baseboard heating elements. Many of these “tried and true” systems use standard or somewhat higher than normal efficiency boilers, but the overall system efficiency is usually much lower due to standby losses of high mass boilers, flue gas losses, sidearm water heaters, and other distribution inefficiencies in such “Old School” system designs.

Not only did this facility have a daycare center with small kitchen, but it also had two large meeting and exercise areas, a large lobby, and two large locker and shower rooms. There was a larger than normal domestic water load and the need for high amounts of ventilation air to serve these many diverse areas in order to meet ASHRAE 62.1 and 90.1 efficiency standards.

Sutton Engineering Services decided to do something a little different—maybe you could call it “new school.” Instead of oil-fired, they decided to go with environmentally superior and clean-burning, low NOX, propane gas-fired equipment, using three ultra high-efficiency modulating condensing boilers from Laars, Inc. and a tekmar Controls boiler-staging controller. The sidewall venting of these high-efficiency boilers using CPVC piping allowed the architect to eliminate the masonry chimney entirely from the structure. In addition, the small footprint of the multiple ultra high-efficiency boilers saved in overall clearance and spacing requirements to help minimize the mechanical room dimensions. A phased construction approach also required that only enough capacity be built at once, but the system would have to be capable of the future second phase of construction. Two boilers met the requirements of the first phase, and one will be added for the second phase when needed.

The main building heating and ventilation design consisted of three boilers with modulating controls, two separate energy recovery ventilators for the daycare and other spaces, two heating and ventilating air handlers with mostly overhead exposed round duct distribution to the exercise, lobby, and meeting areas, and a radiant underfloor heating system for the entire daycare area using Pex-Al-Pex tubing. The radiant floor heating was desired in the daycare area over other forms of heat. The main building heating system was separated from the large domestic water load by dedicating one additional and separate 96%+ efficient boiler and indirect storage heater tank to that purpose. This allowed the entire building heating plant to be shut down during summer operations. Compare this to having a commonly designed cast iron boiler sitting with huge amounts of standby losses, and the associated inefficiency of using a sidearm or indirect heaters that require the boiler to be kept warm all summer. Also, the turndown ratio of the three modulating boilers and use of the tekmar controller allowed for an incredible overall system efficiency at full and part loads. The wheel-type high-efficiency energy recovery ventilators from Greenheck Inc. allowed for fresh air makeup to all areas and for exhaust and relief air from all areas, including the toilet and locker rooms, without the need for additional fans on the roof. There was no kitchen ventilation requirement since the small kitchen did not have a kitchen hood. The energy recovery units were placed in an insulated mechanical attic area.

A primary-secondary system pumping arrangement was provided to allow for separation of the radiant and higher temperature water heating systems, and to also hydraulically separate the heating loads from the boilers. The use of the P-S pumping system also allowed for the second phase boiler to be easily added without any difficulty.

Tekmar variable speed injection pump controls and Taco, Inc. fractional horsepower wet-rotor pumps, along with underslab sensors and programmable zone room thermostats, maintain the radiant loop and room temperature. A separate tekmar and Honeywell Excel 10 controller are set up to handle the water loop and air handler control for face and bypass control of the warm air heating systems.

By using state-of-the-art design, ultra high-efficiency boilers, and sophisticated but simple hydronic and control technologies, this facility will able to enjoy the benefits of its heating system for years to come.