Page 46 - Zero Net Energy Case Study Homes-Volume 1

CASE STUDY NO. 2 FORTUNATO HOUSE RENOVATION
(Opposite page, top) Interior view, Second Floor at Office, showing deep overhang shad- ing large glass areas for view and daylight.
(Opposite page, bottom) Inte- rior view, First Floor at Family Room.
(energy-recovery ventilator)6. Although ideal in terms on automatic control of minimal required flow of fresh outdoor air, this system requires some ductwork for the air distribution.
Instead, for this case study house, the owners first made an effort to determine potential sources of such unhealthy chemicals, both in the construction materials and household products, and to eliminate them. The thermal chimney, as well as kitchen and bathroom ventilation fans, remove any remaining unhealthy air contaminants, moisture and cooking odors. Continuous air move- ment through the rooms of the house is accomplished by having the operable windows at the top of the thermal chimney (central stairwell) slightly open at all times of the year. As a result, there is minimal but steady air flow induced in all the rooms via this natural ventilation mechanism. Given the care in eliminating the sources of air contaminants, the owners did not feel that it was necessary to incur the cost of the more elaborate HRV system. No sensoring system is installed, however.
Heating, Ventilating and Cooling Systems
An air-source electric heat pump integrated with an 80 gallon water storage tank was selected as the basis of the design for heating because of its inherent efficiency, a choice that works well in some renovation projects. The heat transfer medium is heated water, which can be easier to integrate with an existing structure than air ducts and is a more energy efficient medium because it does not involve energy-consuming fans or duct losses. The hot water is piped through mani- folds that are controlled by thermostats in each room; it is then delivered to the room’s hydronic baseboard units.
The heat pump’s normal cooling capability is not used because of the house’s efficient design and the relatively benign marine climate.
Domestic Hot Water
The domestic hot water (DHW) is provided by a separate 50-gallon electric heat pump water heater. In addition, a drain water heat recovery unit is installed at each of the shower drain lines, which captures some of the heat energy from the draining water as it is piped to the exiting grey- water line. Each cold line from the water main to the showers is first run to the drain water heat recovery unit before going to the shower mixing valve. This essentially provides preheating of the input water and reduces the amount of hot water needed.
The system design also uses a recirculating pump at the sinks in the kitchen and upstairs bathroom, which are the longest runs for the hot water piping. (Originally, this was occupancy- sensor-driven—see Post-Occupancy section.) These pumps save water and energy by using the cold water line as a return pipe to the hot water tank until the water in the hot water line reaches high temperature. (This can be a considerable amount of time because of the distance from the hot water tank.) This is in contrast to the normal situation where the water from the hot water tap goes down the drain while the water at the sink gets hot enough to use.
Lighting
The owners have replaced many of the original compact fluorescent lamps with LED sources in the past few years, which has had a beneficial effect in lowering energy used for lighting. In addi- tion, glare-free daylight from well-shaded, large window areas, as well as daylight penetration in the middle of the house provided by the central stair space, create a sense of balanced daylight and openness throughout the house. As a result, use of the electric light sources is largely un- necessary on most days.
6 See M. Holladay, “HRV or ERV?”, Green Building Advisor (January 2010), www.greenbuild- ingadvisor.com. The HRV provides reassurance of consistent high quality IAQ without undue air leakage. The tradeoff is the introduction of a low-wattage fan that operates continuously.
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Zero Net Energy Case Study Homes: Volume 1