Our company recently set a new corporate record for the largest residential job we have ever performed. It just also happens to be the greenest job we have performed to date as well. The project also set a record for the longest running job we've ever performed on a residential basis.
We started the design process more than three years ago. We began meeting with the homeowners and their construction consultants, architects and engineers to discuss their wishes, wants and needs on this project. They had initially hired a mechanical engineer, who generated a set of specifications based on previous conversations with the homeowners.
What they wanted was the ability to have heating and cooling available in certain parts of the home during all seasons of the year. They wanted radiant floor heating in the common areas, as well as in the bathrooms. The man of the house also wanted radiant floor heating in his garages. The lady of the house wanted the quietest system she could find because she had always been a light sleeper and was constantly awakened by the noisy heating and cooling systems turning on and off in her previous homes. They also wanted to have an automatic snowmelt system that worked because they had experienced three previous snowmelt systems that had performed poorly, if and when they turned themselves on.
Lastly, the homeowners wanted the systems to be as energy efficient as was technically feasible, at this point in time, with the caveat that they also had to be economically feasible and tempered by a dose of reality.
Initially, we had discussed the possibility of incorporating solar thermal into the picture, but due to their frequent travel, it was decided that they probably weren't good candidates for that type of system.
We then decided that because the local electric utility is required to buy back electricity generated by its customers, that it made more sense to install photovoltaic solar than it did thermal solar.
They had originally contacted another company, which I'm associated with, regarding the potential application of a ground-source heat pump. The company is a regular subcontractor of ours who normally performs the installation of ground-source heat pump systems up to the buffer tanks for us. They realized early on that they were probably not qualified to run a job this big and decided to take a back seat and allow our company to work as the prime contractor. In any case, ground-source heat pumps for heating, cooling and domestic hot water preheating were part of the project early on.
The mechanical engineer had specified some of the most stringent noise and vibration standards we had ever been exposed to, primarily due to the homeowners wishes to have the quietest system possible. This required us to specify and install some items that we didn't typically install in a residential setting, like rubber-mounted pipe vibration isolation collars and flexible connectors to allow the ground source heat pumps to operate without transmitting their vibrations to the distribution piping systems. It was also decided early on that the indoor sections of the ground-source heat pumps serving the second floor sleeping areas would be installed in the attic of the second floor, as far away from the sleeping quarters as possible. The units that were serving the second floor sleeping quarters were also double hung with vibration isolation spring mounts to avoid the possibility of transmitting vibration to the home's framing members.
In addition to providing the heating and cooling needs of the home, we were also responsible for providing humidification during the winter months, fresh air ventilation through heat recovery ventilators and ultra air purification through the use of electronic air filters.
All told, we had 22 wells for the ground-source heating and cooling needs of the building. We had five total ground source heat pumps, two of which were water-to-water heating/cooling units, and three air heating/cooling units. That is just the ground-source equipment.
We also needed two modulating/condensing boilers to augment the heating needs of the main floor and to also insure domestic hot water sanitization temperatures that are hotter than could be achieved by the ground-source heap pump systems alone.
The equipment we had chosen is only capable of providing pre-heated DHW to around 115° F, and we recommend a holding temperature of 130° F to avoid bacterial amplification. Space was tight, so we used a reverse indirect for providing DHW preheat and the required buffer tank needs for the ground-source heat pump system.
Tune in next month as we continue to review the largest, greenest residential system we have installed to date. Until then, Happy Bright Green Hydronicing!
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.