Mansion House Heat Recovery Saves $17,000 Annually
The Mansion House is the largest hotel on Martha’s Vineyard as well as the greenest. They use the 16,000 gallons of groundwater that they pump out of the basement on a daily basis as a source of cooling for their air conditioning system – turning it into a hybrid open/closed geothermal system.
For 9 months out of the year, there is an excess of heat available in the geothermal building loop that has been collected from all of the heat pumps in all of the rooms. While this heat is fairly low grade, in the range of 85 F to 95 F, there is a lot of it and it is free. We developed a multi-phase project for the Mansion House to use this free source of energy to heat the swimming pool and pre-heat domestic hot water. Our calculations determined that the Mansion House would save $17,000 annually from this project in displaced fuel oil purchases for the five heating boilers.
The first phase was to repipe the pool heating system to incorporate new circulators for both the pool itself and the geothermal heat exchanger system.
We then installed a new circulator that would send geothermal building loop water through a plate and frame heat exchanger. The other side of this heat exchanger would be connected to the pool heating system.
Because the hotel is continuously occupied, we used “hot taps” to connect our heat exchanger pipes to the geothermal building loop. This meant that heating and cooling was uninterrupted in the hotel during our work.
The plate and frame heat exchanger worked very well and fuel oil use in the boilers dropped significantly. We were able to successfully extract heat from the geothermal building loop in the peak summer months of cooling operation to heat the pool. The pool was uninsulated so it lost a lot of heat all year-round and our target pool temperature was 82 F. That meant that if the geothermal building loop temperature was higher than 85 F, we could successfully heat the pool with the heat exchanger.
The success of phase one led the way to phase two – capturing free heat from the geothermal building loop for use with pre-heating domestic hot water. Because there was no room for additional water storage tanks in the basement, we designed a pre-heat system that used a much larger plate and frame heat exchanger to heat the incoming cold water (at 50 F) up to 85 F or more in a single pass. To accomplish this, we ended up with a plate and frame heat exchanger that had front and back plates that weighed 800 pounds each and were 2 feet wide, almost 7 feet tall, and 2″ thick!
She navigated the lobby….
And waited for the elevator….
and the mock-up just barely fit in the elevator!
and she was in the sub-basement and almost there!
Here is little Nina holding up the foam mock-up in the spot where the actual heat exchanger will go.
As with the plate and frame heat exchanger for the pool heat, we installed a circulator to send hot geothermal building loop water through the much larger plate and frame heat exchanger for domestic hot water pre-heat.
We installed the back plate with concrete anchors and used “hot taps” to connect the heat exchanger pipes to the geothermal building loop.
We made the final connections, purged out the air, and started up the circulator. The circulator sent hot geothermal building water through one side of the plate and frame and cold potable water was pre-heated in the other side. After several years of operation, our savings figures have been shown to be conservative and the project is a resounding success.
Our goal is to be Martha’s Vineyard’s premier plumbing and HVAC shop – we appreciate the opportunity to show you some of our work.