Favorite Multifamily Retrofits, Part 2
Energy Storage, Low-Flow Aerators, and Ventilation
Which retrofit is better: changing the boiler or changing the lighting? There are so many possibilities for multifamily buildings that choosing the best retrofit depends a lot on your definition of best. Are you after the most cost-effective option? Then low-cost or no-cost fixes like adjusting equipment settings will probably win. Are you interested in massive energy savings? Then a deep energy retrofit involving everything from envelope to equipment is probably needed.
Steven Winter Associates (SWA) has been recommending energy-saving retrofits for multifamily clients for many years. Choosing the "best" retrofits among these is pretty difficult, but over the years we've come to appreciate a few more than others. We offer you a look at six of our favorites. In a recent issue of Home Energy (“Favorite Multifamily Retrofits, Part 1”), we described advanced controls for electrically heated buildings; combined heat and power systems; and upgraded atmospheric boilers. For three more options, keep reading!
Peak Shaving Profile
Installation of a Shower Regulator
Flow by Floor: Bath Ventilation
Table 1. Ventilation Economics
Energy Storage Systems
Multifamily buildings are part of an increasingly complex energy landscape. Increased use of intermittent renewable-energy sources like wind and solar challenges utilities to maintain a steady energy supply. Large-scale energy storage systems such as banks of batteries have been imagined for years as a way to even out the peaks and valleys of supply and demand, but until recently, they have been prohibitively expensive and impractical. With the falling cost of high-performance batteries and the rising capabilities of intelligent power management strategies, energy storage systems will soon have their day in residential buildings.
SWA has been conducting a research project for the New York State Energy and Research Development Authority to assess the feasibility of using batteries to store energy in multifamily buildings. Preliminary results indicate that batteries may be used for this purpose in many buildings, with possible paybacks as short as two to five years. Utility companies and grid operators are interested in incentivizing the use of battery systems as well, because batteries can help them control demand for grid energy.
Today, in the age of ultra-high-performance net zero or near zero energy buildings, batteries are being integrated with renewable-energy sources. Electricity from solar power may be stored in a battery system during the day and used at night. This results in a synergy, because PV output and electrical demand are often both high on sunny days. Multifamily buildings tend to have peak demand later in the day (from 4 pm to 10 pm), so energy stored during the midday generating peak can be used during the evening demand peak. Batteries are being integrated into more complex systems with cogeneration, solar power, and emergency backup functions.
Many readers will be familiar with the concept of demand response. Periods of very high demand, such as on hot summer days, may threaten the stability of the electric grid, so grid operators may ask customers to voluntarily reduce their energy consumption to take strain off the grid. This might simply mean temporarily turning off lights, A/C compressors, and pool pumps, or scaling back thermostat set points, but batteries can participate in demand response as well. By discharging during a demand response event, they become in effect separate power-generating stations, taking some of the load off the grid by powering all or part of a building. So far, only very large battery banks (>100 kW capacity) have been able to participate in demand response, but this may change.
Peak Demand Shaving
Electrical demand is most often calculated by measuring the power consumption at the meter over 15-minute periods, and charges are often based on the average of the highest two consecutive such periods. For some buildings, demand charges may make up 40–60% of the electric bill, amounting to a major expense. Buildings with high relative peaks tend to have intermittent and/or weather-dependent loads, such as air conditioners, intermittent pumps, and the like. They create demand during only part of the day. By contrast, 24/7 corridor lighting is an example of a load that does not generate a relative peak.
Batteries can help mitigate demand charges by shaving the peaks off a building’s electrical use profile—discharging during a peak and lessening the building’s draw from the grid. An example of reduction might look like the graph shown in Figure 1. The peaks that would occur during periods of high demand are handled by the battery system. The battery then recharges during periods of low demand. The best buildings for this application tend to have large peak loads, such as a chiller, cooling tower, or cooling pumps on a single electric meter.
Another way to use energy storage is to take advantage of changes in electricity prices. For large customers today, and probably for many more customers in the future, the price of electricity will change from day to day. By storing energy when it is cheap and discharging when it is expensive, an energy storage system can lessen the sting of high electricity prices. Some buildings can participate in day-ahead pricing, in which the utility publishes its predicted rates for the next day, and the customer adjusts its usage accordingly. Ten Barclay Street, a 58-story multifamily building in downtown Manhattan, installed a system with 1,000 kWh operating storage capacity in its basement. The system is large enough relative to the size of the building that the utility placed it on a special standby rate usually reserved for buildings with their own generators. Installed and controlled by Demand Energy Networks, Incorporated, the system saves the building’s owner, Glenwood Management, more than $80,000 a year through a combination of peak load management, demand response, day-ahead pricing management, and standby electric rates.
SWA has partnered with the Natural Resources Defense Council to assess the feasibility of using batteries for resiliency—that is, the ability to maintain power during emergencies. Most emergency services, such as exit lights, are designed to operate only long enough to get people safely out of the building. But what happens when the power goes out for a long time in a very dense urban area, where the only reasonable thing is to keep people safe in their buildings until power is restored?
Hurricane Sandy, which cut power in parts of New York City for days, made resiliency a top priority. Smart application of batteries may have a place in situations like this, providing low levels of power for safety and habitability. Having a bit of light in stairwells, powering pumps for sanitation, and perhaps having some outlets for charging cell phones, would go a long way toward making a building habitable for several days. Of course, we don't expect to have emergencies all the time, and having batteries for emergency backup saves no energy. Still, energy storage integrated into the rest of the building, especially with renewables or cogeneration, is an intriguing possibility. Glenwood Management, following its success at 10 Barclay Street, is installing similar systems at several properties in New York.
Considerations for Application of Batteries
Since large-scale installations of batteries in multifamily buildings are still relatively new, the learning curve is still steep. Deciding where to place the batteries is one challenge. The weight of tons of batteries is so great that they need to be placed either in structurally reinforced areas or on the ground floor. Local fire codes may prohibit certain kinds of batteries as well, but this is starting to change, and most energy storage companies can use any of various types of battery (lithium-ion, lead acid, and so forth), depending on the application.
Energy storage systems are becoming feasible for a variety of multifamily buildings, and there will be a need for them in the increasingly complex energy landscape of the future. Large buildings may be able to make use of their capabilities for demand response or peak shaving. Buildings that use renewable energy may find storage systems to be a complementary technology, especially when emergency backup is needed. In short, battery energy storage technology for multifamily buildings is here to stay.
Tamperproof Low-Flow Aerators
Every energy auditor knows that low-flow faucet aerators and showerheads are a straightforward way to reduce water and energy use. They make an immediate impact, and they’re usually easy to install. Unfortunately, they’re also easy to uninstall or modify. SWA audits of multifamily buildings often find flow rates as high as 5 gpm from bathrooms that have had their low-flow showerheads or sink aerators tampered with or removed by dissatisfied residents. Luckily, there are ways to prevent this from happening.
First, it is essential to tell residents what is going on—that is, that the building is trying to reduce its energy use and its environmental impact. Residents who were used to a virtual waterfall for a shower will have to form new habits. Second, make sure to try out a few different showerheads before you commit to installing a given model in a whole building. It sometimes helps to give a showerhead to the building superintendent or a few residents to try in their apartments first, so that they can advocate with the other occupants if they like the new showerhead.
One of the main problems with many showerhead and aerator models is the ease with which residents can remove, replace, or modify them. Many have restrictor rings that are easy to pop out with a screwdriver to increase flow, and even those with nonremovable restrictors can be drilled out or easily replaced entirely. Luckily, there are some ways to make these retrofits more permanent. For faucet aerators, tamper-resistant models are available that have a free-spinning outer ring which cannot be unscrewed with a standard wrench. They can be installed or removed only with a key. The key is supplied with the installation kit, and the super should retain a few copies.
There are also many products designed to reduce water waste from existing toilets. These include tank bags and containers, flapper and seal replacement kits, and overflush diverters, none of which is truly permanent. In the end, the best long-term solution lies among the high-performance, low-flow toilets on the market today. Again, some owners will want to test a few different models before they commit to retrofitting a whole building.
For showerheads, another innovative option is to reduce the flow rate before it even gets to the fixture. The Water Scrooge sells a device (see photo) that is installed in the wall behind the showerhead. The installer removes the existing shower arm, installs the regulator, and reinstalls the shower arm (Figure 2). The device sets an upper limit to the flow rate available at the showerhead. The result is that overflow does not occur at the shower, regardless of what showerhead is used. Even if the showerhead is removed entirely, the in-wall regulator prevents overflow.
This innovative device is quickly installed, and unlike a standard showerhead, it is not easily removed. Since it is installed in the wall, it is not visible and so is less likely to be tampered with. It cannot be removed with ordinary household tools, but a plumber can remove it with common plumber’s tools.
Case studies of savings from showerhead and aerator retrofits abound. The Water Scrooge, for example, installed aerators, shower regulators, and toilet overflush diverters in over 3,500 apartments at
Parkchester North Condominiums in the Bronx. The price of about $200 per apartment included materials and labor, and the total for all apartments came to about $700,000. Water savings of more than 22% resulted, based on water bills for two years before and two years after installation. The devices yielded more than $1 million in savings projectwide, with a payback of about eight months, and Parkchester expects to continue to realize these savings. While we almost always recommend low-flow fixtures and aerators, building owners and their contractors should consider installing tamperproof models when conducting all future energy audits.
If you've ever really looked inside multifamily exhaust ventilation systems, you'll know that they can sometimes be the most poorly constructed part of a building. Understandably, they’re not treated with the same importance as life safety systems or plumbing, but often they’re never checked for functionality at all. Fortunately, today’s high-performance building professionals can inspect and test these systems, and can often retrofit them to greatly improve their function. We have written about multifamily ventilation retrofits in the past (see “Multifamily Ventilation Retrofits for Energy Savings,” HE Nov/Dec ’12, p. 42), and since then SWA has conducted many more such retrofits and has learned some valuable lessons.
Completing many ventilation retrofit projects in the New York City market has given SWA and our contractors a good sense of the potential complications. The most annoying of these involve gaining access to the ductwork, which is more difficult in occupied apartments. Questions immediately arise. If a major problem in the ductwork is discovered, will the contractor have permission to cut into the wall to get access? Who is responsible for patching the access hole? Of course, the more prework inspection you do, the better you will know what you are getting into. As always, time equals money.
Typical ventilation retrofits can often require duct sealing, and this can be done in various ways. Methods range from manually applying mastic, mastic-backed tape, and other sealants to using remote-controlled robot mastic sprayers to using automated processes such as Aeroseal. This last is a proprietary process that consists of applying particles of sealant suspended in air and injected into pressurized ducts. Often, a retrofit will use a combination of several methods.
A full clean/seal/balance retrofit can produce astounding improvements in performance. In one college dorm retrofit, the original extremely poor distribution was delivering about 50–90 CFM of ventilation into the apartments closest to the fan, while the apartments farthest from the fan were getting reverse flow into their apartments. Most apartments had very little. The college decided to conduct a trial retrofit of a few shafts first. After construction debris was removed from the shafts, many large holes were sealed, Aeroseal was injected into the shafts, and constant air-flow regulator (CAR) balancing dampers were installed, the distribution was nearly perfect. Almost every apartment received about 30 CFM of ventilation as specified (see Figure 3). In the end, the retrofit cost about $520 per register, and the college decided to do the whole building.
Why was this retrofit such a success? First, the retrofit took place during school breaks, so the contractor was able to enter the dorm rooms easily, resulting in extremely fast turnaround. Second, the ventilation shafts were mostly vertical, allowing quick inspection, easy comprehension of the layout, and few horizontal/vertical transitions, which can be problem spots. Third, the gypsum board shafts themselves were wide and straight, creating little friction and pressure loss compared to a small-diameter metal shaft. Sealing the shafts and the register connections and installing the balancing dampers was enough to dramatically improve performance.
The economics of ventilation retrofits are not always straightforward and are best approached conservatively. In our earlier article, we explained how to measure ventilation rates and estimate savings. For estimating retrofit cost, that article cited a figure of roughly $350 per register as a good starting point, including labor and materials in the NYC market. While this figure may be accurate for some projects, experience in more buildings has shown us that larger and more complicated buildings can be more expensive.
Only significantly overventilated projects or those with expensive heating fuel will be worth the cost of the retrofit from a purely economic standpoint. More recent figures for full ventilation retrofits in New York, including cleaning, sealing shafts, installing balancing dampers, and changing fans, yielded costs ranging from $300 to $700 per register. Factors that increased cost include condo or coop ownership of apartments, which can complicate access; complicated floor layouts, which make for more complicated duct layouts; and poor existing duct construction (especially drywall shafts).
Energy savings are derived from reducing overventilation and eliminating duct leakage. With less duct leakage, the fans need to exhaust less air to get the required flow from the apartments. Following is an equation for estimating the cost of heating air to replace exhaust:
In this equation, 1.08 is the factor for the mass of air times 60. HDD is heating degree-days. Heating system efficiency is the total seasonal efficiency.
Infiltration factor is the effect of ventilation on the building’s natural air change rate. This factor can be estimated at 0.7 for simple midrise multifamily buildings in heating climates.
Although many factors influence both the cost of a retrofit and the desired savings, some generalizations are possible. Table 1 shows that the more expensive the fuel and the colder the climate, the less ventilation reduction is needed to break even economically. For example, in the New York City climate of 4,500 heating degree-days, if a building is heated by natural gas at $1.20 per therm, 19 CFM of ventilation reduction per register is needed to break even on this project. By contrast, if the building were heated by electricity at $0.15 per kWh, only 7 CFM of ventilation reduction per register would be needed, and at $0.20 per kWh, only 5 CFM per register would be needed.
These prices, which are typical of NYC buildings, show that it is much easier to make an economic case for an electrically heated building than for a gas-heated one. Extrapolating this to a simple 50-unit building with 100 registers, a retrofit cost of $35,000 would require 700 CFM reduction total in the building heated by electricity at $0.15 per kWh but 1,900 CFM if the building is heated by natural gas at $1.20 per therm. This table assumes a very generous 15-year payback on a retrofit. Of course, the building owner may also require a faster payback than 15 years.
See an interesting article on residential use of energy storage batteries.
Get information about the Water Scrooge.
Getting to a high level of performance can mean a substantial investment for some systems, and justifying the retrofit on the basis of energy savings alone will probably work only in significantly overventilated buildings in cold climates with expensive fuel. But there really is no good reason why a bad ventilation system should not be included in a responsible whole-building retrofit as a major quality of life and health improvement. While a full cleaning, sealing, and balancing may be expensive, there are almost always less expensive options. Short of a full retrofit, here are the things that every auditor should consider, in rough order of importance:
- Fix the biggest problems first: poor connections at the roof curb, duct disconnects, and poor duct repairs over the years.
- Seal every crack or gap in the system you can get your hands on. Especially fix any gaps at the final connection between the register boot and the apartment drywall.
- Reassess the size of fans. It’s often possible to find out what ventilation rate they were designed for by looking up the fan and motor nameplate info, and consider changing the fans if they are oversized for current needs.
All these actions will only bring the system to a basic level of functionality, but sometimes that can make a huge difference.
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