Page 27 - Zero Net Energy Case Study Homes-Volume 1

Heating, Ventilating and Cooling Systems
Since the houses exceeded even the Passive House standard for airtightness, it was necessary to add a fresh air ventilation system to each house similar to the typical Passive House design. Normally, this can be accomplished using an HRV or ERV3 system, the preferred ventilation system of Passive House. Fresh air is circulated throughout the house using a very low power fan, with the outside air exhaust near the same location as the air intake so that an energy exchange can occur. Such systems are used to create good indoor air quality in general, which is necessary for airtight houses, while at the same time providing a method of thermal energy recovery from the outgoing air stream..
At the Corona del Mar houses, however, a similar system is used but without the heat exchange component. Continuously operating low-power exhaust fans located in the bathrooms combined with fresh air inlets at another location in the house are programmed to provide the right amount of fresh air to the house. They can provide high speed exhaust when necessary and revert to the continuous operation mode as dictated by the automatic settings.
Both houses utilize electric air source heat pumps, thus providing both heating and cooling ca- pability. The heating /cooling coils are located at the heat pump in the utility area in the garage and an air distribution system much like that used by a conventional furnace ducts heated or chilled air to the various house spaces. The supply air vents were placed in the floors because of the insulation system that was used in walls, with enclosed duct chases to the various locations. Separate thermostats on each of the first and second floors provide two separate zones for heat- ing and cooling, with the resulting potentially better comfort levels on each floor.
An alternative approach, not used in the Corona del Mar houses, would have been to pipe the heated and chilled water to the individual spaces and use a ductless mini-split unit4 to provide good individual temperature control in each space. The room units resemble a floor-monted radiator. (This ductless mini-split system is discussed in subsequent case studies in this book.)
Natural Ventilation
The house at 703 Heliotrope utilizes a “pop-up” roof monitor above the central corridor on the second floor, with operable clerestory windows. The idea was to provide a means of ventilating the house with fresh outside air instead of using the mechanical cooling system. By opening the clerestory windows, the high space would act like a “thermal chimney”, drawing air in at the ends of the house and exhausting it through the clerestory windows at the top.
The owners soon found that using this feature also admitted outside noise and unfiltered air—it was a very quiet house with good indoor air quality because of the airtight design. The result was that they decided not to use that potentially energy-saving feature. It also led them in part to the decision to omit the feature from the house at 609 Marigold, which was also a construction cost reduction measure.
Lighting and Plug Load
The two houses are equipped with LED light fixtures throughout, which significantly reduces the energy used for lighting compared with fluoresent sources. With that reduction, the most signifi-
3 For a description of these fresh-air systems, see http://www.greenbuildingadvisor.com/blogs/ dept/musings/hrv-or-erv
4 For a description of this ductless mini-split heat pump system, see: https://www.energy.gov/ energysaver/heat-pump-systems/ductless-mini-split-heat-pumps.
Zero Net Energy Case Study Homes: Volume 1
15
CORONA DEL MAR NEW HOUSES CASE STUDY NO. 1
(Opposite page, top)
703 Heliotrope interior view.
(Opposite page, bottom)
609 Marigold interior view.