With the Biden administration setting aggressive goals for reducing greenhouse gas emissions, building owners and operators should expect increasing emphasis on energy efficiency in the years ahead.
Energy efficient buildings were the focus of a session at the recent ULI Spring Meeting which discussed technologies that would enable net-zero buildings, that is, buildings that only consume as much energy as is generated on site. The technologies discussed were building envelopes, heat pumps, solar panels, sensors/IOT and battery storage. Each is discussed in a section below:
Half of a building’s energy use may be due to heat loss through the building envelope so having a high performance building envelope is a necessity for reducing energy consumption. While the envelope must control the exchange of vapor, heat, moisture and air with the surrounding environment, the heat and air barriers are the keys to achieving energy efficiency.
Buildings are evaluated on their Total Energy Demand Intensity (TEDI) when looking to reduce their energy usage. TEDI is the sum of the total energy loss through the building envelope plus the total energy required for ventilation divided by the building’s total floor area. Having a rating of energy use per square foot of space allows buildings of different sizes to be compared to one another. Having a low TEDI is a prerequisite to achieving net-zero.
A building may have passive systems, active systems and renewable power generation systems that all contribute to its net energy consumption. However, the building’s passive systems are the foundation upon which its efficiency rating is built. To achieve high efficiency, the building must have highly insulated walls, high performance glazing, air-tight assemblies and minimized thermal bridging.
Thermal bridging is when a thermally conductive path, like a metal beam, extends from inside of the building envelope to the outside, allowing heat to flow into or out of the building. Today, there are accurate modelling tools available that allow a building’s design to be analyzed for energy efficiency prior to construction or renovation. These tools have been particularly improved in their ability to analyze thermal bridging. The tools can be used to evaluate alternative designs in order to find the most cost-effective way to achieve the building’s energy efficiency goals prior to undertaking construction or renovation.
Traditionally, furnace and boilers have burned fossil fuels to heat building interiors or to provide hot water. In order to avoid the resulting carbon emissions, an alternate source of heating is required. Air source heat pumps are the leading alternative.
Air conditioning and refrigeration systems are examples of heat pumps. Rather than creating heat, they use a refrigerant along with a condenser and evaporator to move heat from one zone to another. Because they are just moving heat, they can be 3 to 4 times more efficient than furnaces and boilers in terms of heat provided for a given amount of energy consumed.
An air conditioning system moves heat from inside a building to the outside. In order to be able to also provide building heating, the system must be modified so that the direction of heat flow is reversible. This is done by incorporating a reversing valve to allow the direction of heat movement to change.
Different types of heat pump systems are available for building heating and cooling. For small buildings, mini-split systems are the right choice. For large commercial applications, variable refrigerant flow systems are used.
While replacing an operating building heating and cooling system with a heat pump is probably cost prohibitive, building owners and operators who are looking at replacing an air conditioning system that is at end-of-life might consider installing a heat pump system.
When thinking about achieving net-zero buildings, renewable power generation is part of the equation. Usually this means roof-top solar photovoltaic systems. These systems generate low voltage DC power from sunlight and use a power inverter to convert that into alternating current electricity that can be used by the building’s existing systems.
The two key questions in configuring a solar system are, who will own it and will the power be consumed on site or sold off site. The system can be owned by the property owner or by a third party. The power can be used to meet the needs of the property or it can be contracted to be sold to other power users.
Smart sensors enable active systems that can help reduce the energy consumption of a building. These can include smart lighting sensors that set the light level in a room and thermostats that set the temperature in a room based on occupancy.
Smart sensors can also gather real-time data from the building. The data can be uploaded and analyzed in order to optimize the power consumption of the building in order to achieve net-zero.
While the first application for battery storage that may come to mind is to provide power when the sun isn’t shining, its role in a renewable energy future extends beyond that one. This is already the case in Hawaii where the super-abundance of solar power production has caused power companies to prohibit new solar installations from returning power to the grid lest the grid be destabilized by the intermittency of the solar power. While a power grid can handle the on-and-off nature of solar or wind power when it comprises a small portion of total power demand, this may not be the case once these types of distributed renewable power sources become commonplace. Under those circumstances, on-site storage of any excess power generated by the site’s solar collectors may be the only option for putting it to use.
Even in the absence of on-site renewable power generation, there may be a case to be made for installing battery power storage systems in situations where power companies based their pricing on peak power demand. By charging the batteries during off-peak times and using the stored power to reduce peak demand, properties may be able to reduce their power bills significantly.
Incorporating these technologies into a building’s design may not guarantee that the building will get to net-zero, but they will reduce the building’s energy consumption well into the future.
The session moderator was Marta Schantz of ULI. Presenters were Heather Elliot of Entuitive (building envelopes), Doris Han of BlocPower (heat pumps), Victoria Stulgis of Black Bear Energy (solar panels and battery storage) and Ben Dwyer of Siemens Digital Enterprise Business (sensors/IOT).