In 2010, OF was approached by the Philadelphia Office of Housing and Community Development (OHCD) to determine if they could salvage an affordable housing development, located in the Logan section of the City, on which OHCD had been working unsuccessfully for several years with a local Non-Profit CDC. Prior designs were inefficient and had come in over budget. The funding, which was earmarked for the project through the Philadelphia Redevelopment Authority (PRA) and HUD, was imminently at risk of being returned to HUD due to inaction. OF was told that the project, once designed and permitted, had to be built in no more than three months. They were asked not simply to design the project for the CDC but to act as co-developer and take full responsibility for the logistical, financial and technical success of the project. The requirements were simple: design and build three much-needed homes for this community that would house large, formerly homeless, families, with a handicap accessible ground floor, within the budget and time frame allotted. This project would be the first new construction to take place in this community within the last 50 years. The budget averaged $130sf for Hard Construction costs. There were no “green” or “sustainable” requirements specified for the project.
This project would be a “first” for OF in several ways. It would be their first subsidized housing project, their first project constructed in a modular factory and their first attempt at a Certified Passive House. The homes are simply and efficiently organized, with a handicap-accessible ground floor living, kitchen, bathroom and bedroom. The second and third floors have three more bedrooms, two bathrooms and one office. The buildings are set back from the sidewalk, to match the adjacent neighbors and create planters and a front porch for community engagement. The orientation of the building follows the urban grid in this part of the city, which is not ideally oriented for maximum southern exposure, however, shading devices on the South/West face of the buildings appropriately provide shading in the summer and allow for maximum heat gain in the winter. A 5Kw photovoltaic array on each home maximizes the area that each roof offers and is designed to, as defined through the Passive House Planning Package (PHPP), enable these houses to achieve Net-Zero-Energy-Capability.
Also, essential to the experiment, was challenging the standards by which architects, urban planners and Municipal Housing Authorities conceptualize “subsidized/social/affordable housing”. OF saw an opportunity to define “social” housing as the best rather than the cheapest, fastest and often most ill-conceived forms of housing. They were interested in testing whether it was possible to narrow the gap (or maybe even eliminate it) between “market rate” and “subsidized” housing; exploring whether subsidized housing could also be inspiring, filled with light and life, high-quality, high-performance, long-lasting and healthy materials and systems; whether it could equally have the ability to encourage its inhabitants to be conscious-of and care-for their environments. Most importantly, it was an experiment to see if it could all be done within the budgets that Federal and Municipal subsidies typically support. They saw the potential for this project to demonstrate not only a new standard of performance but also design of housing in general for the City if not the country. They saw the potential to demonstrate with this project, not a prototypical building as much as a prototypical system of building that was replicable, scalable and capable of enabling any building to radically reduce it’s energy consumption and then generate the remainder of the energy that it needed to survive, particularly in urban environments. They saw the opportunity to demonstrate how one the oldest forms of urban housing, the “row house”, could still remain relevant and, in fact, an essential partner in addressing issues of climate change, social inequity and urban blight.
S U S T A I N A B L E B U I L D I N G S Y S T E M
An “affordable”, high-performance, building system that could be replicable at large scales drew OF to modular construction. Scale is critical to the success of any manufacturing process, and repetition is key to efficiency and affordability.
Similarly, scale matters when designing a Passive House. It is easier to design affordable Passive HOUSING than it is to design an affordable Passive HOUSE. Large multifamily buildings have smaller surface-to-volume ratios than single-family detached homes, and therefore inherently have less opportunity for heat loss, making large buildings, purely from a building physics perspective, more efficient. More simply stated, the benefits of scale, as they relate to affordability in both modular construction and Passive “Housing” design, are perfectly aligned.
Typical 2x6 and 2x12 wood framing was chosen as the base structure and thermal envelop, primarily because it was what the production crew knew best. The materials were also inexpensive and readily available. In order to simplify the detailing of the air-barrier layer, they placed it on the outside of the framing and had it double as the moisture barrier. They then placed continuous layers of polyisoscianurate rigid foam board on the exterior of the framing. Triple pane windows sit flush to the exterior air barrier making air sealing between them and the wood framing extremely simple and as “fool-proof” as possible. Beyond this exterior insulation layer on the walls, a vented but closed rain-screen system finished with a mix of metal panel, concrete board and brick was employed.
There would be no opportunity to perform a pre-drywall blower door test on these houses (often preferred during the construction of a Passive House) because the air-tightness of the individual modules could not effectively be tested until they were installed, with seams sealed, on-site. Several experiments were performed during the energy-modeling phase of the project in which the team compared the importance of thermal resistance (i.e., insulation) versus air-tightness in the overall performance of the building’s thermal envelope. While both are critical to the performance goals of a Passive House, slight reductions in air-tightness have a significantly larger impact on Specific Primary Energy Demand than similarly slight reductions in the thermal resistance values of the envelop. This is one of the most important lessons the team learned during the project and has helped to further hone their Sustainable Building System as well as their detailing. Luckily the blower door test measured .4ACH50 for each home, 30% tighter than the .6ACH50 required by the Passive House standard! Thermal imaging provides a visual representation of just how tight the homes really are.
M E C H A N I C A L S Y S T E M S
After exploring several options for heating/cooling/ ventilation for these three story homes, OF’s collaborating mechanical engineer designed a cost effective and “coupled” air-source heat pump/ventilation system using an off-the-shelf, inexpensive yet efficient 9000BTU Packaged Terminal Air Conditioning (PTAC) heat pump unit and an Energy Recovery Ventilator (ERV). Domestic hot water is provided by a Heat Pump Water Heater (HPWH) and placed in the laundry room so that it symbiotically works to reduce heat and humidity generated by the condensing dryer and washer.
The mechanical room was located on the third floor so that fresh-air intake and exhaust air ducts would come through the roof. It was decided early on that the homes would be “all-electric”, no natural gas. Gas would have been another costly service, it would have required venting for several appliances, and therefore, more punctures in the thermal envelope and the potential of heat loss and air leakage. Gas is also a non-renewable resource that can’t be generated on-site and would contradict the intention of the project as Net-Zero-Energy-Capable.
E N E R G Y M O N I T O R I N G
A significant and robust energy, temperature, humidity and CO2 monitoring system was installed in each home within the Belfield project. Every electrical circuit is monitored for energy consumption and the production of the 5Kw PV system covering each home’s roof. Temperature sensors are placed in each room in the house, with two CO2/humidity sensors positioned on upper and lower levels. All data is collected through a monitoring hub and managed through a website unique to each home. The monitoring is absolutely essential to understanding not simply how the home performs but how the occupants live within the homes.
The data, from three identical houses, shows widely ranging energy consumption. Analyzing each circuit the team discovered a complicated and fascinating story of occupant behavior, property mis-management and a need for significant education.
A snapshot was taken of one month’s energy consumption (February, 2013), which demonstrated monthly electricity bills ranging between $72.00 and $226.00. The circuits in the homes consuming the most were the “Laundry” circuits. In one home it was recording an average of 104 loads of laundry in 30 days! The HPWH circuit demonstrated that the water heater was effectively running in purely electric resistance mode, not Heat Pump mode, most of the month. The heat pump inside the HPWH has a COP of 2.5, which means that it is 2.5 times more energy efficient than an electric resistance water heater.
The hot water alone was accounting for $107.00 of this home’s $226.00 utility bill. This also demonstrates a larger, unexpected issue. The team discovered that this one home has been effectively running a small Laundromat, with friends and family coming by to clean their clothes daily, given that Laundromats are common for most people in this neighborhood and that private washers and dryers are an unaffordable luxury. The team did not account for the potential impact that this one social and economic construct would have on the energy demand of these homes. The washer and dryer in this unit running so continuously has also caused other unintended consequences such as significant heat build-up in the home. While this is not problematic in the winter, it contributes considerably to the cooling load and energy consumption in the summer. Other significant anomalies were discovered between the homes’ energy consumptions. In one home, during February and March, the indoor air temperature was consistently being maintained one or two degrees above the set 70 degree thermostat temperature, even though the heat pump rarely turned on. At first the team was pleased, thinking that their Passive House was doing exactly what they expected, i.e., maintaining it’s indoor air temperature and comfort levels with nothing more than the internal heat loads of people, lighting and appliances. Looking more closely, however, they discovered unusually high plug loads coming from several rooms, which they discovered, upon inspection, was the result of electric resistance strip heaters tenants had plugged-in throughout the home. This was not because the rooms were cold, but rather simply because they owned them, as they had been accustomed to using them in their prior drafty residences. On several occasions when the team would visit the homes to check on problems they were seeing in the monitoring data on-line, they’d arrive to homes in the middle of the winter, with windows and doors open, tenants with shorts and t-shirts on and complaints of variations in temperatures between floors and rooms.
As one might imagine, the performance of the houses have fallen short of their projections. With 12 months of data, while these houses were consuming between 25% and 66% more energy then they were designed to consume, two of the units, using roughly the same energy, 6-7 kWh/sf/yr (Site energy), are still the lowest energy homes OF has ever built and roughly 65% more efficient than a typical American home built to code. And while occupant behavior might appear to be an easy target for not meeting the Passive House projections, the primary culprit is actually much more obvious and unfortunate: the Non-profit CDC that owns and operates the properties does not charge its tenants for electricity! As such, there is no incentive for tenants to be conscious of their energy consumption. In other words, the property owners place NO VALUE on energy consumption. Even with that significant management flaw, after subtracting the energy generated by the PV on the roofs of the units, the homes still, on average, require only between $32 and $93/month to operate all utilities. Armed with this data, OF has approached both the owners and tenants of these homes in order to hopefully transform both occupant and management behavior and narrow the gap between human and building performance.