Energy Savings Prompt Boiler Retrofit
October 19, 2009
It’s not every day that a contractor has the pleasure of replacing equipment he installed more than 30 years ago. But that is all in a day’s work for Angelo Sardinha, a second-generation hydronic-heating expert of M. Sardinha & Son Plumbing & Heating, Fall River, Mass. He recently replaced the five 300,000 Btu cast iron atmospheric boilers he installed years ago at the Truesdale Clinic, also in Fall River, Mass., with three 94 percent efficient condensing boilers.
The clinic was not having any problems with the existing boilers; however, Sardinha noted that their age was becoming a concern, as was their energy efficiency. “The boilers were getting older, and they weren’t as efficient as newer equipment. We had already retrofitted two other boiler rooms for them with energy-efficient equipment, and since those turned out so nicely, the clinic decided to upgrade these older boilers as well.”
The doctor-owners of the Truesdale Clinic are pleased with the retrofit - and especially with the money they have saved since the new boilers were installed in June 2008.
TEXTBOOK RETROFITThe new boilers that Sardinha installed serve the oldest section of the clinic: A two-story, 22,000-square foot structure that was built in 1960 and now consists mainly of doctors’ offices and medical examination rooms. The five older boilers had formerly sat in a row on the floor, and Sardinha is pleased to note that not only did the replacement installation involve two fewer boilers, but he was also able to save even more space by stacking two of the three units. “The metal cabinet makes it easy to stack the units, so there is no need to build separate racks to save floor space.”
Sardinha recommended ModCon condensing boilers from Heat Transfer Products for the retrofit because of their energy efficiency, and the ease with which they could be installed. “The only issue that was maybe a little unusual during the installation was we had to have a roofer come in and make penetrations in the roof for the exhaust. That was it,” he said.
Each of the three boilers was equipped with a 4-inch concentric venting kit, consisting of a smaller PVC pipe within a slightly larger PVC pipe. Exhaust exits up the inside tube, while fresh makeup air is drawn into the boiler through the larger, encasing pipe. Since the structure was single-story in this part of the building, Sardinha chose to run his vents through three roof penetrations - one for each boiler - rather than running the lines through a nearby chimney that extends fully 40 feet into the air.
Condensing boilers operate at a significantly higher efficiency than their conventional atmospheric counterparts by squeezing a much higher fraction of the latent heat energy from the gas-combustion process. This, in turn, results in lower exhaust temperatures, permitting vent runs made of low-cost, installer-friendly plastic piping instead of traditional B-vent metal venting.
Rather than firing full bore with every call for heat, the gas burners in these condensing boilers match their outputs to the available heat load. In the case of the three units installed at Truesdale, their outputs range from 100,000 Btuh to a maximum 500,000 Btuh; that is, a five-to-one turndown ratio.
The five-to-one turndown ratio for each boiler actually translates into a combined 15-to-1 ratio for all three units, which use a control to sync their operations and stage their firings to meet the required load. This means the clinic has 1.5 million Btu for the coldest days of winter, but as little as 100,000 Btu for those spring and fall days when far less heat is needed.
Sardinha noted the controls were easy to use, and he likes the communication that takes place between the boilers. “We just tie in the three boilers, and they all talk to each other.” The controls also significantly contribute to energy savings, because when the system reads the outdoor temperature, it can automatically adjust the boiler output temperature according to whatever parameters are programmed into the system. The result is a much more comfortable environment for the building’s occupants, while also saving energy and costs.
ENERGY SAVINGSSpeaking of saving energy and costs, that has certainly been the case at the Truesdale Clinic. During their first 11 months of operation, the three new boilers cut the clinic’s energy consumption by 38 percent. During the coldest winter months, gas savings ranged from 15.9 to 49.8 percent compared with the year-ago period.
The three boilers operate year-round, which also helps ease energy costs. In addition to providing wintertime space heating, the boilers also feed two 45-gallon indirect water heater tanks, with one of the boilers generating domestic hot water daily and the other two serving as backup. During the summer months, the latter pair also supplies a small amount of warm water to the buildings’ outmoded, but still-effective, 1960s-era hydro-air cooling system.
Pulling fresh makeup air from the outdoors, two large coils chill this airstream before directing it through ductwork to cool the building. On their own, the chillers produce a steady supply of 50°F air, which over time would leave occupants chilled, even on the hottest of days. Consequently, the boiler hot water loop is periodically used to warm the chiller coils just enough to create a more comfortable interior temperature.
The entire replacement installation took just four days, and one of the cast iron units was kept in place for three of those days, so that the clinic would not have to go without hot water for very long. Since then, the clinic has watched its gas bills and maintenance costs decline, which has made Sardinha - and the owners of the clinic - very happy.
Publication date: 10/19/2009