Resources for Green Living in the Chesapeake Bay Area

This essay is written to assist homeowners in pursuing sustainable technologies in mechanical and electrical systems for their homes which will both ease utility bills and benefit the environment. Much has been written of late about the benefits of environmentalism in the construction industry, and this article is meant to supplement those thoughts with more specific examples of sustainable ideas for the home, as well as the means to implement them.

When clients approach my firm wanting to embrace sustainable concepts for a new building or renovation, we like to tell them to save the energy first, before thinking about the actual mechanical or electrical systems. The most energy efficient system is the one that is turned off. In other words, you should begin your sustainable upgrades by making sure that your home is insulated, especially at the roof. Other areas of this website can assist you in providing insulation to an un-insulated area of your home or improving the performance of your windows, so I will not go into specifics here. Just keep in mind you can only save as much as you spend, so save the money first by keeping the mechanical systems off.

For a residential owner the most sustainable (in my opinion) option for heating and cooling would be an electric heat pump which is ground coupled through and underground piping loop to reject heat or take heat from the Earth. This type of system is more commonly know as a geothermal system, even though it still uses the refrigeration cycle within the system. These systems are the most efficient heating and cooling option available through the physics of how the systems work, which is illustrated in the diagram below:

On the inside of the home, the ground coupled system looks the same as a standard split system air conditioner or heat pump. The air handling unit is located in a mechanical space and is ducted to supply registers throughout the house, and a return air path brings air back to the inlet of the air handler. The cost of the installation on the air handler and distribution system inside the home is the same whether you choose a ground coupled system or a typical residential split system.

The difference in the two system choices is outside of the home. A typical split system has a condensing unit sitting on grade or on a roof which rejects or takes heat from the atmosphere. In a ground coupled system this component goes away and is instead replaced with a well drilled into the property which circulates water through the Earth and into the condenser of the indoor air handler. A pump must also be provided with the system to move the condenser water through the well and through the heat pump. The picture above is a bit misleading with the amount of wells. I have found that smaller homes need one well for about two tons of cooling, while bigger homes can use two or three wells for 5-6 tons of cooling. The well consists of a 6” diameter bore hole three-four hundred feet down, with a supply and return pipe installed in grout to the bottom of the hole. Most installers will warranty this installation for life. A house or shed can be constructed on top of the well or wells. The wells are not visible from the outside of the home. Usually the condenser water lines stub into the basement of the home below grade through the foundation wall or up through the basement slab. The cost of each well installation is three to five thousand dollars, and that is the only additional cost with this system. We have found paybacks on these systems to be between five to ten years.

If your home has an existing hot water heating system or you prefer the comfort of radiant heating, then my recommendation is to replace a traditional gas fired boiler with a condensing type boiler with digital controls. Most condensing boilers come with factory installed digital controls that can connect to a room thermostat and control boiler water temperatures instead of simply cycling the boiler on and off as traditional systems do. As you modulate a condensing boiler’s hot water temperature, the boiler flue gases start to condense inside the boiler and the efficiency is raised from 80%, which is a new, standard boiler efficiency, to 95%, which is typical for a condensing boiler. The result is a sharp decrease in natural gas bills and extended period of the year where the boiler is not firing.

Since the flue gases will now condense with this type of installation, some modifications may have to be made to your home to install a condensing boiler. The first thing you will need is a drain at the bottom of the boiler connected to the sanitary system for the condensate spill. If your boiler is installed on a basement slab, this may be a costly installation. The second thing to consider is that a condensing boiler cannot use a typical steel Type B boiler flue or chimney, since the condensate will damage the flue. The condensing boiler must be installed with PVC pipe as the chimney, usually 4” in diameter. This flue can terminate through a side wall of your home as long as it is 12” from any window or door. The condensing boiler also needs an air intake piped with PVC to the outdoors. This can be run along with the vent pipe, also through the side wall.

The photo below shows a condensing boiler installation into an existing hot water heating system. The piping and pumping can remain the same. Notice the PVC pipe intake and exhaust out of the top of the boiler. The new digital controller is visible on the top of the boiler as well. This particular boiler, Weil Mclain Ultra, will also ship with an outdoor air temperature sensor which you place on an exterior wall and wire to the controller terminal strip. The hot water temperature is lowered even further as outdoor temperature rises, saving even more in gas utility bills. It should be noted that condensing boilers are currently unavailable (in this country) for an oil fired application. They must be installed wih natural gas or propane only.

If the timing is not right for a major upgrade of your current heating or cooling system, then a minimal cost item with a big impact on energy savings is a digital wall thermostat, available for about $100 at any of the big box stores. These thermostats have a built in seven day time clock, which you can program to lower the temperature in your home during the winter when you are away at work during the day or sleeping in the early morning hours, and raise the temperature during the same times in the summer. Installing these devices in a home previously using a typical dial thermostat can save up to 25% of your energy usage for heating and cooling.