Part 3: Learning How Florida Homes Work
The Florida Solar Energy Center is Florida’s independent energy research institute and part of the University of Central Florida. We are a state energy research laboratory and I’d argue that our efforts have been unparalleled in experimentation and measurement of energy efficiency and renewable energy technologies applied to housing in Florida. Homes are key to the energy picture in Florida since more than half of the total state electricity consumption is used in the residential sector: 118,453 GWh in 8,786,683 households in 2016.
Since the 1990s, our institution has enjoyed a very productive research relationship with Florida Power and Light Company. We have also experienced a very beneficial research relationship with Florida Power Corporation (FPC) and what is now Duke Energy Florida. In the late 1990s, with FPC, we studied how radio-dispatched demand load control could reduce utility system peak demand in over 200 homes that were monitored.
Often with cooperative funding from the U.S. DOE, we learned a lot about how to cut energy use in Florida homes relative to a variety of issues. We know Florida’s climate is unique relative to cooling and humidity. But what matters most?
Categorized as demand side management research in the 1990s, we evaluated many promising technologies and also measured how electricity was used in homes. Perhaps most importantly, in 2012, we began a project with both U.S. DOE and FPL called the Phased Deep Retrofit Project (PDR).
In the PDR project beginning in 2012, we monitored 60 homes in Central and South Florida in great detail (minute data) and with copious data on the homes and their energy using systems. Then, over a period of two years, various retrofits were installed in the homes — both easy (shallow) and extensive (deep) as well as evaluation of various advanced energy-efficiency technologies. For this project, we learned extremely significant lessons about how to really cut energy use in Florida homes, which we will cover in greater detail in future columns. The short of it: saving 9–10% of energy use in Florida homes is easy and cheap. Saving an average of 40% of energy use in existing Florida homes is more expensive, but still cost effective if approached in a staged fashion when equipment and systems need replacing.
As seen in Figure 1, air conditioning (cooling) is the largest electrical end use in Florida homes. Accordingly, over the last three decades FSEC has gathered unique information on what drives cooling loads in Florida houses. In very detailed field monitoring done with FPL, we discovered, for instance, that reflective white colored roofs in the state could cut space cooling by 15–20%. And this information was so valuable that it led to roofing manufacturers creating cool colors and also made provision in the Florida code to assist homes looking to improve efficiency.
And that success for improved energy efficiency from reflective roofs contrasted with the research topic almost everyone associates with efficiency – added wall insulation. That popular efficiency target showed air conditioning savings of only about 5% in spite of very careful pre- and post-monitoring.
Within the research, we were able to see why — roofs and attics get very hot from exposure to the Florida sun and also contain the cooling ducts which gain lots of heat from the attic. Walls, on the other hand, receive less sun and often are shaded by trees, landscape, and other buildings, such that realistic savings from lots of wall insulation in Florida is quite limited. The thermal driving forces on walls are much lower. At the same time, we learned that having ducts in a Florida attic is an engineering disaster. This doesn’t take much thinking: you cool down air to 55°F, then pass it through a spreading octopus of R-6 ducts in an attic that reaches 120°F — 20–30% of the cooling is lost before it even reaches the registers in the ceiling. Tragic.
However, we did show — as reflected in the state’s building codes — roof solar reflectance really matters and matters a lot. And so do interior ducts — get the ducts out of the attic or find a cooling solution that does this (multi-split heat pumps). In fact, recent research has shown that adding a supplemental very high-efficiency mini-split heat pump to an existing central AC system can save 33% of cooling from that one change. Moreover, it is possible to purchase such systems, up to 17 SEER — powered by 120 volts. (The 240 volt mini-splits are up to SEER 33! See Fujitsu 9RLS 34.) These are available from Home Depot for as little as $730. Thus, with a generator or batteries with rooftop solar after a hurricane, it would be possible to provide precious cooling continuously.
Figure 2 shows an analysis we did of a typical existing Florida home in Central Florida that would be similar to the monitored PDR homes. The twin pie charts show the simulated annual heating and cooling loads for the building by specific component: walls, windows, ceilings, doors, air leakage, and duct distribution system. The chart for heating is much smaller than for cooling, reflecting that the magnitude of air conditioning energy needs in Florida are more than 10 times those for heating. Note for cooling that ceiling heat gains and that to the duct system counts for more than a third of total air conditioning needs while walls (which everyone tends to focus upon) are only about 10%. This would indicate that the retrofit of added ceiling insulation and changing to mini-split air conditioning equipment which doesn’t suffer duct conduction or air leakage would likely save a lot as described above.
At the same time, windows are about 20% for both heating and cooling. Although we have learned that better windows can save energy, there are real limits to what can be saved by the technology of windows and the need for good visible transmittance. Exterior shading is always more effective than relying only on the glazing properties.
One often overlooked facet seen above is that heat gain from interior appliances is responsible for 20% of cooling needs. It is one of the largest cooling load components. Whereas heat from people and appliances in a cold climate provides much of the space heating needs, in hot climates it is opposite. Heat from less efficient lighting and appliances adds to air conditioning loads. Moreover, it can be shown that as insulation is dramatically increased, this problem becomes greater. Appliance heat gains in superinsulated buildings can lead to overheating under mild outdoor conditions. Of course appliance heat gains cut both ways, but in Florida we have little heating needs to suffer the downside of reduced interior appliance heat.
Given our very beneficial relationship with the Florida utilities, we began to learn about one technology after another that might help overall household efficiency: reflective roofs, better insulation, energy-efficient lighting (LEDs), variable speed cooling systems, better duct systems, smart thermostats, more efficient refrigerators, more efficient clothes dryers, and cutting “phantom loads” from stuff plugged in but not doing much other than using power while sitting idle.
Then the idea: after a lot of meaningful individual evaluations, what if rather than evaluate one technology and the next, we combined them all at once? What would happen to energy use? The computer simulations said it would drop to astoundingly low levels– a fact explored in Europe at about the same time with the Passivhaus concepts.
During the early 1990s, Jim Dunlop (who was studying residential photovoltaics) and I started to look at the idea of optimized extremely efficient building envelopes and equipment when mated with solar PV power production — a technology that was just new and nascent at that point. Not only did we show that this might be possible, but in 1998, we built two side-by-side homes in Lakeland, Florida, with exactly the same floor plan but differing (only) in the equipment, envelope measures, and systems. Beyond demonstrating nearly net-zero electrical requirements when evaluated over the year, we found the gallery of technologies reduced space cooling by more than 70%! This was a big moment — the birth of “Zero Energy Homes” that later became a full-scale program for the U.S. Department of Energy and continues even today.
We showed that with high levels of efficiency, with conventional Florida houses, it was possible to build homes that had such low electricity needs that the solar PV on the roof of the homes could take care of the remainder of the annual requirement. And development over time of distributed (or site) electrical storage foretold the possibility of largely energy-autonomous neighborhoods. We further examined using the building’s thermal capacitance to shift peak loads. Very detailed data were collected on the buildings, which then served as a role model for NREL’s new Zero Energy Home Program.
The project was an oft cited success — although, one seldom duplicated, at least in Florida.
Yet, how to get this kind of success moving ahead in Florida’s housing? Retirees dominate here with no state or utility efficiency incentives, and PV at the time was very expensive. Not surprisingly, there was a lot of interest, but not many copies. Although, through the U.S. Department of Energy’s Building America program, we did continue the research.
But what about the millions of single family homes throughout Florida that gulp power all summer?
Seeing the success of the Zero Energy Homes concept, I began altering my own 1957 vintage home in Cocoa Beach. Could I do something similar even with an existing home? By patiently changing systems and equipment and improving the house envelope over the years, we were able to show that not only was net-zero energy possible over the course of a year, but I could also add a plug-in hybrid electric automobile (Chevy Volt) and still be at net zero. We composed a detailed report showing how I did the whole thing.
How I accomplished this is clearly shown by years of recorded data at our home showing how electricity use has been reduced with efficiency and then increased by such things as remodeling and adding rooms and appliances for growing kids.
In recent years, we’ve added a second plug-in hybrid electric vehicle — a Ford C-Max Energi for my wife, Lisa. My home has not been a laboratory, but a real household of four with two kids. Still, we showed how to reach net-zero annual energy in a very difficult climate in an old Florida house. It was done by balancing efficiency and renewable energy and carefully selecting equipment. Daily data on the home performance is still available: http://infomonitors.com/dpr/
Moreover, you can end up with a home better able to maintain comfort long after power interruption after major storms. I did it; so it must be possible.
Why aren’t more households doing it? Rather than just a paper study, why not use the findings from something like the Phased Deep Retrofit project to profoundly improve the energy efficiency of Florida’s housing?
Shouldn’t Florida utilities be helping homeowners to make the best choices?
In the next segment, we’ll explore how the potential benefits for consumers get lost and what might be done to move things in a better direction.
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