Page 96 - Designing for Zero Carbon-Volume 2_Case Studies of All-Electric Multifamily Residential Buildings

CASE STUDY NO. 4
THE PALO ALTO APARTMENTS
(Above, Top) Excerpt from plan drawing of Townhome showing location of heat pump for space heating/cooling and for heat pump water heater.
(Above, Middle) Condenser of Fujitsu heat pump for space heating/cooling.
(Above, Bottom) Rheem heat pump water heater at interior location.
Heating, Ventilating and Cooling Systems
The all-electric design approach is most dramatically featured in the heating, ventilating and cooling systems of the individual apartments. Each of the thirteen apartments has its own heat pump system. Because each apartment has separate bedrooms, and therefore several zones for heating or cooling, the heat pump is essentially a “multi-split” system with separate fan units for each zone.
The penthouse unit and the larger of the two townhomes have two heat pumps to accommodate the extra number of zones in those larger units. Because the airtightness characteristics of the apartments are good but not extraordinary, the developer opted not to install an Energy Recov- ery Ventilator (ERV) for additional energy savings and indoor air quality5. The tenant is encour- aged to open windows for fresh air ventilation in the benign Palo Alto climate.
Domestic Hot Water Systems
Each apartment unit has a separate heat pump water heater located in an exterior closet. This unit has the hot water storage tank built with the small heat pump unit attached at the top, requir- ing a tall closet to house it.
Appliances
The third heat pump in each apartment unit is a heat pump dryer. Ductless heat pump dryers avoid creating negative air pressure in the apartment, unlike standard dryers, which duct the warm moist air to the exterior, wasting energy and unavoidably sucking possibly-polluted outdoor air into the apartment. The heat pump dryer sends the warm moist air through an evaporator, which removes the moisture without losing much heat. The result is that less electric energy is used to generate the heat for the dryer appliance’s air.
The second major electric appliance in this project is the induction cooktop. While a standard electric stove could have been installed for less initial cost, the induction cooktop performs much better for the cooking process because of the amount of immediate control possible, comparable to the responsiveness of a gas or electric resistance burner. The better safety characteristics, indoor air quality and energy efficiency of the induction cooktop made it the preferred choice for the developer.
The kitchen exhaust air fan is specified to be low-powered compared with the standard high-air- volumeexhaustfanssincesuchlargequantitiesofairflowarenotneededforinductioncooktops compared with gas, where indoor air pollution created by gas stove combustion byproducts requires a significantly larger volume of air removal. The result: a significant reduction in energy use.
Lighting, Plug Loads and Control Systems
All lighting, which is energy-efficient LED-source, is dimmable from a smart control system app on a mobile phone6. The control system can be operated remotely and additional electric devices can be added, such as the heat pump settings, the door locks, security cameras, the wifi hub and appliances. Each of the apartments is capable of becoming a “smart home” with this system and its electric devices.
5 For a complete discussion of the use of an ERV in an airtight house, see p. 12 in Case Study No. 6 of Zero Net Energy Case Study Homes, Vol. 2, (2020).
6 Samsung SmartThings app, https://www.samsung.com/us/smartthings/.
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Designing for Zero Carbon: Volume 2