Entry # 121

Homer Senior Assisted Living Building

Designer: Nathan White

Customer: Homer Senior Center

Installation Location: Homer Alaska

Brief overview of the project

We were asked to convert the 25 year-old heating system from oil heat to natural gas while making energy saving improvements along the way.  The existing system had two 1.2 million BTU oil boilers to provide heat and hot water to the 40 bed complex.  The hot water was created in two 250 gallon cement-lined tanks with tube and shell bundles in them and the heat for the building is via baseboard and convectors.  First thing I noticed on inspection of the heating plant was the three-way mixing valve for the building heat was broken and  bypassed allowing 190 degree water to the baseboard and convectors; according to the labels on the mixing valve controller the system was originally designed for 170 degree temperature.  Next I opened up all the zones in the building and read the differential pressure on the system pump and noted the Delta T so I could calculate exactly how many BTU's the building was using.  I also measured one of the rooms for a heat loss calculation and multiplied it times 40.  The end result was a calculated 450,000 to 500,000 BTU's at max load (pump vs calc).  The plan was to upgrade to high efficiency modulating condensing boilers for the building heat and a dedicated high efficiency domestic hot water heater.  We would utilize ECM circulators everywhere possible to help improve overall system efficiency and comfort.  We utilized a Caleffi 4" ASME HydroCal separator in our design which allowed for us to operate the boilers at a 40 degree Delta T and the system at a 20 degree Delta T. Since we were utilizing ECM circulators with permanent magnets in our design and this was a remodel we wanted to make sure we had a good magnetic separator in the system.  Since the SEP4 hydro separator from Caleffi is not available in 4”, we ordered up one of Caleffi’s first 4” ASME DIRTMAGs in the USA and installed it in the system. A ¾” Caleffi 5350 high flow AutoFill with Presscon connections was used for the system fill.  After the system was up and running we noticed that with the large 7:1 turn-down ration on the boilers we needed to add some resistance to the near boiler piping to help keep a nice wide Delta T when the boilers were firing at 14-19%, so we added a Caleffi 142 variable orifice balancing valve into the supply or return line on each of the boilers.

Design goal

The goal was to convert the system to the newly available natural gas in the area and help the senior center save money on its day-to-day utility cost so it can upgrade other facilities in the future.  The biggest challenge was keeping the building operational while we did the upgrade.  We first pulled one oil boiler and disconnected one hot water generator. So that way the building could still be heated and have hot water off the remaining oil boiler.  Then we installed the new 600 Armor in place of the old oil boiler and piped up to the tank we had disconnected and rebuilt.  Once we had the Armor up and running we disconnected the other hot water generator and rebuilt that tank and tied it in.  By now, the summer days were getting warmer and heat was not a big concern so we took down the heating system and installed the two FTXL600 boilers and ECM pumps.  Thanks to the HydroCal and the smaller foot print of the FTXL boilers the boiler piping was condensed allowing for a lot faster upgrade.  On this project we were given free range to make improvements to the system and we did.  We upgraded all of the buildings thermostats to digital battery-less stats that they could set a high and low limit on. We upgraded the DHW recirculation line to and ECM circulator with a digital timer.  The boiler pumps were also ECM pumps that varied their speed with the boilers firing rate to try and keep the designed Delta T across the heat exchanger. The system pumps were upgraded to ECM circulators as well. They automatically switch back and forth between the two pumps for equal run time and redundancy. We installed a Leonard master mixer as well when we upgraded the domestic hot water system, since the building never had one.  This added scald-guard safety and allowed us to raise the stored tank temperature to 145 degrees which eliminates any Legionella threat and increases total system capacity.

Installation description

This was a retrofit to a 25 year-old oil heating and domestic hot water system.  The system piping outside of the boiler room was nicely done and balanced with circuit setters 25 years ago so we didn't touch that other than replacing 12 bad zone valves we found.

System performance

The system is performing incredibly well.  The high efficiency FTXL boilers with the 7:1 turn down, outdoor rest, coupled to the variable speed boiler pumps so as to achieve a 40 degree Delta T worked out very nice.  The system temp at max design temperature ended up at 160 degrees, so the boiler is always running in condensing mode with the 40 degree Delta T.  The baseboard and the convectors are nice and comfortable operating at the system's 20 degree Delta T.  This was all possible thanks to the 4" Caleffi HydroCal which also serves as the system's sole air eliminator and it is a fine one at that.  We did a 3 month check up on the system and walked through the system with the facility maintenance crew to show them how to dump the DIRTMAG and HydroCal and any other maintenance tidbits they should know.  Over the 3 months, the DIRTMAG and the HydroCal did a great job collecting debris and magnetite from the system water.  The facility is saving thousands of dollars a month in fuel cost alone, not including the electrical savings from the ECM circulators and replacing the electric dryers in the facility with gas dryers.  They couldn't be happier and neither could the tenants who never run out of hot water and are comfortable.  

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