Design Strategies - Design & Construction

Retrofits for enhancing safety, efficiency, and comfort in the home

Graphic of a home with EcoBlock proposed retrofits.
Improved Thermal Comfort

Attic and Floor Insulation, Weather Sealing

Loose-fill or batt insulation is typically installed in an attic. Loose-fill insulation is usually less expensive to install than batt insulation, and provides better coverage when installed properly. See more on different types of insulation.

The Oakland EcoBlock project aims to insulate the attic spaces of participating houses to R-30 (9-16 inches).

Typically before insulating, one seals any air leaks (such as around windows and doors, and through building envelope penetrations) and makes roof and other necessary repairs. The goal of the project is to improve air sealing by 25%.

Efficient Space Conditioning & Water Heating (Heat Pumps)

Heat pump water heaters offer greater savings over gas storage and electric resistance water heaters while providing the opportunity for load shifting and demand response performance. In mild-climates domestic water heating makes up a large percentage of a home’s total energy consumption. The EcoBlock project proposes using both combination systems for domestic hot water (DHW) and space conditioning for heating only and traditional individual heat pumps for DHW and space conditioning (heating and cooling. The combination market is still nascent but there continue to be advancements in product availability and technology. 

The proposed combined system uses the Sanden SANCO2 heat pump water heater (pictured below). Heat pump water heaters offer an efficient electrical option for residential water heating using a refrigerant cycle to move heat from the ambient air to water in the tank. The Sanden unit is designed as a split system to maximize efficiency. 

Diagram of Sanden HPWH Split System
Diagram of Sanden HPWH Split System. Credit: Sanden. Sanden Water Heater



The use of the Sanden heat pump in the combined mode for water heating and space conditioning is practical for high-efficiency new homes and for deep energy retrofits with hydronic heating systems. The Sanden SANCO2 Heat Pump Water Heater is a two-part system consisting of a tank (usually placed indoors) and a heat pump unit. It has a capacity of 15 thousand Btu per hour (kBtu/hr) and can be designed to deliver both domestic hot water and space conditioning load hot water. The system accomplishes this by providing domestic hot water at 120 degrees, using a mixing valve to reduce the temperature, and another line to a standard heat exchanger supplying hot water radiators, radiant flooring, or a forced-air fan coil for space heating. The design load of the building will be within the capacity of the heat pump design temperature for Oakland which is 37 °F degrees outside air temperature. The proposed combination system, as shown in the schematic diagram below, includes the SANCO2 heat pump water heater, outdoor compressor unit, mixing valve, and air handler unit with electronic commutated motor (Eklund 2016).

Schematic Diagram of the Sanden Combinations System
Schematic Diagram of the Sanden Combinations System. Credit: Ken Eklund, Washington State University


The outdoor unit includes the compressor, air-to-CO2, and CO2-to-water heat exchangers, control system, and circulation pump. The heated water is stored in an insulated stainless steel tank in a conditioned space. The outdoor unit is activated when the sensor in the tanks reads a water temperature of 113°F. Unlike other heat pump water heaters that have an electric resistance element, the SANCO2 does not have a backup element and therefore is always run in heat pump mode for maximum efficiency. The Sanden functions like a regular air-source heat pump water heater, but with CO2 as a refrigerant. The CO2 refrigerant allows the Sanden to perform in greater temperature ranges and take heat from a lower temperature than other refrigerants.


The tank and outdoor unit of the system are connected by hot and cold water line connections. Cold water from the bottom of the tank is pumped into the heat exchanger at the bottom of the outdoor unit, where heat is transferred from heated CO2 gas (Eklund 2015). The heated water returns to the top of the tank. The tank temperature can be set from 120°F–165°F. With a higher temperature of 160°F, the domestic hot water uses a mixing valve to bring the temperature to a safe set point of 120°F while the 165°F water can be run through the hydronic air handler unit when heating is called for. The systems will be sized according to domestic hot water loads and heating loads to ensure demands can be met.


Referencing the Eklund et al. (2015) calculations, the sizing parameters and tank size can be determined. There are two tank sizes: 43 gallons, which provides a 71-gallon first-hour delivery, and 83 gallons for five or more occupants, which delivers a 101-gallon first-hour delivery (Sanden Water Heating, n.d.). To have the system function well, the plumbing needs to be optimized. The plumbing of the system will be based on lessons learned from a Multifamily Zero Net Energy EPIC study underway, Optimizing Water Heating Performance for Multifamily ZNE, that is evaluating the optimization of domestic hot water for multifamily ZNE. The project team will be able to leverage that Multifamily ZNE EPIC study to plumb individual and central heat pump water heater systems for the EcoBlock. While research is ongoing, very recent information on understanding the energy use in heat pump water heaters will be leveraged to inform project-specific design considerations for this project. In addition, the MF ZNE EPIC study will be evaluating the opportunity to use heat pump water heaters for load shifting to minimize the cost burden on occupants as well as the grid. To minimize and potentially eliminate energy use for water heating during peak times, the water heaters will be equipped with an after-market timer to control the tank to leverage solar production at peak solar times, heating water to a higher temperature, and eliminate grid energy at peak grid periods. The higher tank temperature of the Sanden is coupled with a mixing valve that can expand a 43-gallon tank to 85 gallons of 120°F water. By extending the volume of available hot water, occupant hot water demand can be met during peak grid periods without utilizing electricity to heat water. The Multifamily ZNE EPIC study will evaluate how to maximize this capacity, and the findings will be used to refine the design of the systems for the EcoBlock.

Indoor Air Quality
Ways to Improve Indoor Air Quality Infographic

Heat Recovery Ventilator

diagram showing inside of a heat recovery ventilator
Credit: Energywise Ireland

Heat recovery ventilators “recover” heat or cools from inside air while providing fresh ventilation air. They reduce the costs of heating ventilated air in the winter by transferring heat from the warm inside air being exhausted to the fresh (but cold) supply air. In the summer, the inside air cools the warmer supply air to reduce ventilation cooling costs. 

  • Reduce heating and cooling costs
  • Available as both small wall- or window-mounted models or central ventilation systems
  • Cost-effective in climates with extreme winters or summers and high fuel costs.

Smart Ventilation

As building envelopes are tightened, it is important to have systems in place to support good indoor environmental quality (IEQ). Conversely, adding mechanical ventilation to a high-performing home adds load when the end goal is to reduce the home’s overall energy consumption. There are several ventilation systems that can support Title 24 ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) 62.2 mechanical ventilation requirements from exhaust only, supply only, and balanced systems. Typical runtime control mechanisms are timer, 24-hour, and/or humidity.

Smart ventilation allows a home to gain demand response savings through a mechanical ventilation system. As defined by LBNL, a smart ventilation system has two goals:

  • Reduce ventilation energy use and cost compared to a continuously operating ventilation system while still maintaining the same or better indoor air quality (IAQ).
  • Allow residential ventilation systems to eventually interact through a process called “short-term load shifting,” which reduces power draw from ventilation systems during the peak demand period.

A monitoring system can shift ventilation run times to meet ventilation principles and save energy. A smart ventilation system will maintain IEQ equivalent to ASHRAE 62.2 with the ability to shift to favorable run times and be able to account for operation of other fans such as bath, kitchen or dyer for on/off signals. 

Smart ventilation systems meeting current Title 24 indoor air quality standards will be installed to support improved IEQ and occupant comfort. The ventilation system will be triggered by air quality conditions such as humidity and/or minimum air changes per hour. 

An Energy Recovery Ventilation (ERV) system (a mechanical ventilation system that tempers incoming fresh air with exhausted indoor air) may be able to address small heating and cooling loads (Figure 2-20). The actual ventilation system to be installed will be determined through the on-site audit.

In addition to whole-house mechanical ventilation, the homes will receive upgrades of spot ventilation in bathrooms and kitchens. The bathroom exhaust ventilation will meet current California Green Building Code and include a humidistat control. The kitchen exhaust specifications to maximize pollutant capture are discussed under the Appliances section below in conjunction with the range.

Efficient Exhaust Fans

Exhaust fans direct stale air inside your home outside, removing unwanted airborne contaminants such as smoke, pollen, and dust. These appliances are typically located in kitchens and bathrooms, where odors, fumes, and moisture easily accumulate due to activities like cooking, showering, or washing.

Today’s modern exhaust fans use DC (Direct Current) Brushless motors or ECMs (Electronically Commutated motors), which are quieter, have a longer lifespan, and consume much less power–less than 10 Watts–than traditional fans. These advantages make DC Brushless and ECMs ideal for use in devices that run continuously (e.g. washing machines, air conditioners).


Natural gas-fueled appliances such as stoves, ovens, water heaters, and furnaces can release carbon monoxide and nitrogen dioxide gases, particulate matter, and other harmful pollutants into the indoor air in homes, which can be toxic to people and pets. Proper venting can reduce these sources. However, a recent in-home measurement by LBNL found that installed hoods over stoves often do not achieve rated or advertised flow rates.

Swapping out gas cooktops with electric induction stoves and replacing gas water heaters and furnaces with electric heat pumps will remove these sources of air pollution from the home, thus improving indoor air quality.


Energy- and Water-Efficient Appliances

Energy and water-efficient appliances (dishwasher, clothes washer, and clothes dryer) will be upgraded to the current ENERGY STAR ratings at a minimum. The ratings for standard dishwasher and clothes washer appliances can be seen below:


Dishwasher ENERGY STAR criteria. Credit: U.S. Environmental Protection Agency



Clothes Washer ENERGY STAR criteria. Note: These criteria were last updated on March 7, 2015. Credit: U.S. Environmental Protection Agency

Smart Thermostats

Smart thermostats are Wi-Fi enabled devices that automatically adjust heating and cooling temperature settings in your home for optimal performance. While system designs may vary, common smart thermostat features include:


  • Many smart thermostats learn your temperature preferences and establish a schedule that automatically adjusts to energy-saving temperatures when you are asleep or away.
  • Geofencing allows your smart thermostat to know when you’re on the way home and automatically adjusts your home’s temperature to your liking.

Credit: Alliance to Save Energy


  • Wi-Fi enabled thermostats allow you to control your home’s heating and cooling remotely through your smartphone.


  • Smart thermostats provide equipment use and temperature data you can track and manage.
  • Periodic software updates ensure your smart thermostat is using the latest algorithms and energy-saving features available.

LED Upgrades

Credit: Department of Energy

The light-emitting diode (LED) is one of today’s most energy-efficient and rapidly-developing lighting technologies. Quality LED light bulbs last longer, are more durable, and offer comparable or better light quality than other types of lighting.

LED is a highly energy-efficient lighting technology, and has the potential to fundamentally change the future of lighting in the United States.  Residential LEDs — especially ENERGY STAR rated products — use at least 75% less energy, and last 25 times longer, than incandescent lighting.

Widespread use of LED lighting has the greatest potential impact on energy savings in the United States. By 2027, widespread use of LEDs could save about 348 TWh (compared to no LED use) of electricity: This is the equivalent annual electrical output of 44 large electric power plants (1000 megawatts each), and a total savings of more than $30 billion at today’s electricity prices.

LED lighting is very different from other lighting sources such as incandescent bulbs and CFLs. Key differences include the following:

  • Light Source: LEDs are the size of a fleck of pepper, and a mix of red, green, and blue LEDs is typically used to make white light.
  • Direction: LEDs emit light in a specific direction, reducing the need for reflectors and diffusers that can trap light. This feature makes LEDs more efficient for many uses such as recessed downlights and task lighting. With other types of lighting, the light must be reflected to the desired direction and more than half of the light may never leave the fixture.
  • Heat: LEDs emit very little heat. In comparison, incandescent bulbs release 90% of their energy as heat and CFLs release about 80% of their energy as heat.

Ceiling Fans

Circulating fans include ceiling fans, table fans, floor fans, and fans mounted to poles or walls. These fans create a wind chill effect that will make you more comfortable in your home, even if it’s also cooled by natural ventilation or air conditioning.

Credit: Department of Energy

Ceiling fans are considered the most effective of these types of fans because they effectively circulate the air in a room to create a draft throughout the room. If you use air conditioning, a ceiling fan will allow you to raise the thermostat setting about 4°F with no reduction in comfort. In temperate climates, or during moderately hot weather, ceiling fans may allow you to avoid using your air conditioner altogether. Unless you are using your ceiling fan primarily to circulate air, turn it off when you leave a room; fans cool people, not rooms, by creating a wind chill effect.

Ceiling fans are only appropriate in rooms with ceilings at least eight feet high. Fans work best when the blades are 7 to 9 feet above the floor and 10 to 12 inches below the ceiling. Fans should be installed so their blades are no closer than 8 inches from the ceiling and 18 inches from the walls.

Larger ceiling fans can move more air than smaller fans. A 36- or 44-inch diameter fan will cool rooms up to 225 square feet, while fans that are 52 inches or more should be used in larger rooms. Multiple fans work best in rooms longer than 18 feet. Small- and medium-sized fans will provide efficient cooling in a 4- to 6-foot diameter area, while larger fans are effective up to 10 feet.

A larger blade will also provide comparable cooling at a lower velocity than a smaller blade. This may be important in areas where loose papers or other objects will be disturbed by a strong breeze. The fan should also be fitted to the aesthetics of the room—a large fan may appear overpowering in a small room.

A more expensive fan that operates quietly and smoothly will probably offer more trouble-free service than cheaper units. Check the noise ratings, and, if possible, listen to your fan in operation before you buy it.

When buying ceiling fans, look for the ENERGY STAR® label; modern DC brushless fans can use less than 30 Watts. Fans that earn the label move air 20% more efficiently, on average, than standard models.

Additional Resources:

Appliances 101: Know your heat pumps Cover
Appliances 101: Heat Pumps
Appliances 101: Know Your Induction Cooktops infographic
Appliances 101: Induction Cooktops
Appliances 101: Know Your Efficient Washers infographic
Appliances 101: Efficient Washers
Appliances 101: Know Your Efficient Dryers infographic
Appliances 101: Efficient Dryers
Appliances 101: Efficient Refrigerators
Appliances 101: Efficient Refrigerators
Appliances 101: Range Hoods cover
Appliances 101: Range Hoods
Retrofits 101: Windows
Retrofits 101: Window Treatments
Appliances 101: Heat Pump Water Heaters infographic cover
Appliances 101: Heat Pump Water Heaters
Appliances 101: Smart Thermostats
Appliances 101: Smart Thermostats
Appliance Energy Usage Infographic
Infographic: Appliance Energy Usage

Explore other EcoBlock disciplines: