There is a common misconception that building green means taking on higher costs to protect the environment. In fact, green design is an excellent financial decision: it reduces the lifetime cost of ownership of a building while reducing its environmental footprint.
Green building enhances corporate image and companies are more likely to attract customers who place a high priority on sustainability. In the case of property developers, a green building will be attractive to tenants who share these values.
This article will describe 20 green design features for buildings that reduce emissions and waste while offering an attractive return on investment. For each eco-design feature described, we will provide general information about cost, space requirements, savings, and payback period. Please note that these are broad estimates and project costs may vary depending on construction conditions.
Get a green building project and save thousands of dollars on energy and water bills.
To describe the performance of green design features, we will assume a 100,000 square foot apartment building with the following characteristics:
Gas, electricity and water bills add up to $42,600/month, or $511,200/year.
1. Cogeneration
Exotic Level: 5/5
Cost: US$1.4 million (200 kW microturbine, material cost US$3,000/kW, total installed cost US$7,000/kW)
Space requirement: Room 400m2
Energy Savings: $195,000/year
Payback: 7-8 years
Cogeneration is also known as combined heat and power (CHP) , and consists of producing electricity and heat simultaneously. Many generation methods release heat as a secondary product, which is typically wasted. However, this heat can be recovered and used for applications such as space heating, water heating and industrial processes.
Cogeneration equipment can be classified into two main types: microturbines and reciprocating engines. Both rely on the combustion of natural gas to drive the generator, and heat is recovered from engine cooling water and exhaust gases.
| PROS | CONS |
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1) Lower electricity and heating expenses compared to 100% dependence on utilities. 2) The cogeneration system can be used as an emergency generator, combining two pieces of equipment into one. |
1) Complex and expensive system. 2) Only viable in installations that require a lot of heating. If this is not the case, relying on public services may be cheaper. |
Hotels and hospitals are some examples of types of buildings where cogeneration is viable. It is also possible to drive an absorption chiller with waste heat, implementing a concept called trigeneration – electricity, heating and cooling simultaneously.
2. Fuel Cells
Exotic Level: 5/5
Cost: Typical cost $2 million, $1.46 million after 26% federal tax credit (200 kW unit, $8,000/kW material cost, $10,000/kW installed cost)
Space Requirement: Typically less than 200 square feet.
Energy savings: US$180,000/year
Payback: 8 years
Fuel cells produce electricity and heat from a chemical reaction, and some types can also be used as energy storage devices. Like cogeneration systems, fuel cells are cost-effective when the heat and electricity outputs can be used continuously.
Unlike batteries, which contain the reactants that produce electricity, fuel cells use an external source and cannot be “discharged”. The reaction can continue indefinitely as long as reactants are supplied.
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1) Compact and lightweight. 2) Some types can be used for energy storage, complementing renewable energy systems with variable production (solar panels and wind turbines). |
1) Financial viability may be affected if fuel prices become volatile. 2) Maintenance is complex and requires specialized labor. |
There are many fuel cell compositions, and two emerging types are very promising: solid oxide fuel cells (SOFC) and hydrogen fuel cells. Bloom Energy Server is an example of a commercially available SOFC, which has been used successfully by technology giants such as Google, Yahoo and eBay.
3. Photovoltaic solar panels
Exotic Level: 3/5
Cost: $400,000 for a 120 kW system (about $296,000 after 26% tax credit)
Space Requirement: About 10,000 square feet of roof area (12 watts/sf roof area)
Energy savings: $44,000 per year
Payback: 6 to 7 years, may be lower with state or utility company incentives
A solar energy system can be an excellent investment, especially if you have a building with a lot of coverage area. Quality solar panels typically come with a 10-year warranty against manufacturing defects and a 25-year warranty against loss of generation, which applies if productivity drops below 80% before 25 years. Some manufacturers may offer enhanced warranty terms.
The US offers a 26% federal tax credit for solar panels in all states, which will be available until the end of 2022.
- In other words, homes and businesses can deduct $260 from their federal taxes for every $1,000 invested in solar energy.
- The tax credit will be reduced to 22% in 2023, and in 2024 it will drop to 10% for businesses and 0% for homeowners.
- The federal tax credit can be combined with local rebate programs and state tax credits, making solar energy even more affordable.
The Tesla solar roof is a promising innovation that adds solar cells to roof tiles. They are expensive to use on existing buildings , as roof replacement is required. However, the concept is viable in new construction, where there is a basic cost of coverage anyway.
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1) The payback period of solar panels represents only a small fraction of their useful life. Your ROI is guaranteed thanks to the guarantee. 2) Simple maintenance, where the main requirement is to keep the panel surfaces clean and free from shadows. 3) May be eligible for incentives from the government or utility companies. |
1) Energy generation depends on sunlight. It ceases at night and decreases drastically in cloudy weather. 2) Finding space can be a limitation in some buildings, due to Fire Department permits and mechanical roof equipment. |
4. Thermal Solar Collectors
Exotic Level: 2/5
Cost: $200,000 ($2,000 per household), $148,000 after 26% federal tax credit
Space requirement: 10,000 square feet of coverage area (same as solar panels)
Energy savings: $20,000 per year
Payback: 7-8 years
A solar collector is a viable alternative to photovoltaic panels, with less savings, but also with a lower initial cost. In this case, solar radiation is used to heat water instead of generating electricity.
When a building has solar collectors, occupants can rely less on electric or gas water heaters. There may be a lower pumping cost in taller buildings since the water has to reach the roof, but it is much less than the ongoing cost of a water heater.
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1) Financially viable: Provides free heating when sunlight is available. 2) Simple installation and maintenance. |
1) No heating at night and limited effectiveness during winter. You need another heating system as a backup. 2) Competes with solar panels for coverage area. If space is a limitation, solar panels tend to offer a better ROI. |
5. Central Cooling Plant
Exotic Level: 3/5
Cost: US$2 million
Space requirement: 1,500 square feet. living room
Energy savings: $187,800 per year
Payback: 10-15 years
Chillers are among the most efficient air conditioning systems for buildings, especially water-cooled chillers connected to cooling towers. Some modern units are even equipped with AI and can dynamically adjust their cooling output to match the needs of the building.
Cooling plants can achieve significant economies of scale by concentrating conditioned air in a single location and making it as energy efficient as possible. Space cooling is achieved with hydronic piping circuits and fan coils, and the system becomes even more efficient when pumps and fans are controlled by variable frequency drives (VFD).
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1) Cooling plants provide one of the most efficient air conditioning options. 2) Achieve synergy with other energy efficiency measures such as VFD units for fans and hydronic pumps. |
1) High initial cost and requires dedicated area for chillers and their complementary systems. 2) A centralized design means the entire building can go without AC if a key component fails. |
6. Geothermal heating and cooling
Exotic Level: 4/5
Cost: $3.33 million, $3 million after 10% federal tax credit ($10,000 per ton of capacity, 300 sf per ton, one well per ton, 333 tons for this building)
Space requirement: Same as a chiller, boiler or conventional oven
Energy savings: $105,000 per year
Payback: 18-25 years
Soil is an excellent heat sink during the summer and a heat source during the winter. Geothermal heat pumps take advantage of this, providing heating and cooling for buildings with lower kWh consumption than other systems.
Indoor heating and cooling is achieved with hydronic piping, air handling units (AHU), and ductwork. The geothermal heat pump uses a secondary water circuit that goes underground to collect or reject heat as needed.
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1) Geothermal heat pumps are among the most efficient heating and cooling systems for building interiors. 2) It can provide heating for the same cost as natural gas (or even less), while eliminating associated emissions. 3) Well field eliminates the need for cooling tower and boiler. |
1) Expensive system that requires specialized maintenance. 2) Not all buildings have suitable underground conditions for a geothermal heat pump. 3) Drilling 200-foot deep piping shafts instead of a simple cooling tower and boiler is a more expensive alternative. 4) Geothermal wells must be spaced about 15 feet apart, so a well field to handle this building is about the size of a football field. |
7. Rainwater harvesting
Exotic Level: 3/5
Cost: $30,000 for a 10,000-gallon system
Space Requirement: 10,000 gallon tank, 141” diameter and 160” height
Water savings: $3,200 per year
Payback: 9-10 years
Humanity has been collecting rainwater for centuries, but the concept has gained more importance in the modern world, especially in places with limited water supplies. Rainwater harvesting requires a collection method and a storage system, and all retained water is subtracted from your electricity bill.
In densely populated areas like New York, rainwater harvesting also reduces the volume of water moved through sewers during a storm, preventing spills. A single building with rainwater harvesting does not have a large impact, but the effect increases when many owners implement it.
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1) Free water supply. 2) Reduce the discharge of treated water from sewers during a storm. 3) Modernizing existing properties using rainwater is relatively simple. |
1) It does not provide a continuous supply of water throughout the year, as it depends on rainfall. |
8. Gray water/black water recycling
Exotic Level: 4/5
Cost: $200,000 ($2,000 per household)
Space Requirement: One 250-gallon tank per household, 36” in diameter and 66” in height
Water savings: US$20,000
Payback: 10-12 years
The concepts of gray water and black water are used to describe water that has previously been used in plumbing installations. Black Water includes water from all equipment while gray water excludes water discharged from toilets.
Although gray water is polluted with cleaning agents and grease, it can be collected for purposes such as flushing toilets or outdoor irrigation. Black water can also be recycled for some purposes, but it requires special treatment.
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1) Reduced water bills: Less water is taken from the municipal supply when the same water is used for multiple purposes. 2) Decongest public sewage. |
1) May not be practical on existing properties where gray water is not separated from black water. 2) Blackwater recycling requires an expensive treatment system. |
Separating gray water and black water is easier in new construction since the plumbing system has not been installed. Water recycling is more challenging in existing buildings, especially if water discharged from all equipment is combined with flushing from toilets.
9. LED Lighting
Exotic Level: 1/5
Cost: $102,000
Space Requirement: No additional space, replaces existing lamps and fixtures
Energy savings: $39,000 per year
Payback: 2-3 years
LED lighting is among the most cost-effective building upgrades, offering a quick payback and a long service life. Furthermore, lighting savings are subtracted from the room's cooling load, saving on air conditioning. LED bulbs also offer a much longer lifespan than incandescent, fluorescent and HID bulbs, meaning replacements are less frequent.
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1) Huge electricity savings: 30-50% less than fluorescent, 50-80% less than HID, 80-90% less than incandescent. 2) Reduced cooling load for air conditioning and refrigeration equipment. 3) Long service life and low maintenance. |
1) High initial cost. 2) Some people prefer the warm glow of incandescent and halogen lights, but this can be solved with LEDs that mimic them. |
10. Natural light
Exotic Level: 3/5
Cost: $10,000 for five upstairs skylights
Space Requirement: No additional space
Energy savings: $2,600 per year
Payback: 3-4 years
LEDs provide low-cost lighting, but only sunlight is free. Natural lighting consists of maximizing the internal use of sunlight, avoiding its two negative effects:
- Glare, which is the visual limitation that occurs when the sun is directly visible.
- Solar heating, which increases the load on air conditioning equipment.
Glare and solar heating can be controlled by optimizing window placement, and skylights can be used in single-story buildings or on the upper levels of multi-story buildings.
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1) Free lighting. 2) Windows and skylights have very simple maintenance requirements. |
1) Unavailable at night. 2) Potential for glare and unwanted solar heating. |
11. Occupancy-sensing lighting controls
Exotic Level: 2/5
Cost: $4,500 for 30 building-wide sensors ($150 each)
Space Requirement: Minimum, same size as smoke detectors and wall switches
Energy savings: $5,250 per year
Payback: Less than a year
LED lighting sometimes has a rebound effect. As occupants are aware that lights are more efficient, they may become careless and leave them on more frequently. Occupancy sensors can solve this problem by making sure lights are only on when needed.
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1) Synergy with LED lighting, enhancing the savings achieved. 2) Occupants don't have to worry about turning lights on and off. |
1) Increases the cost of lighting systems. 2) Compatibility issues may arise when many types of lighting are used. |
Occupancy sensors can be combined with other lighting controls for greater energy savings. For example, they can be complemented with dimming systems that respond to daylight – the lights are only used at full brightness when there is no natural lighting.
12. Passive House
Exotic Level: 5/5
Cost: An additional 10% of the total construction cost, $3.62 million for 100,000 square feet. construction
Space Requirement: Building size is not affected
Energy savings: $333,000 per year
Payback: 10-15 years
Passive house construction comes from Germany (Passivhaus), but applies to all types of buildings, despite the word “house”. Passive house construction relies on maximizing natural ventilation and using high-performance insulation to significantly reduce HVAC expenses or eliminate them entirely.
Passive house construction also optimizes the effect of solar heating, preventing it during the summer and maximizing it during the winter. Any HVAC system used is combined with energy recovery measures to further reduce operating costs.
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1) Large energy savings, which can exceed 75% compared to conventional buildings. 2) Exceeds the performance level required by most energy codes. |
1) It makes the construction project more expensive by 5 to 10%. 2) Limited use in existing buildings, as the surroundings have already been built. |
13. Energy recovery ventilation
Exotic Level: 3/5
Cost: $150,000 ($1,500 per household)
Space requirement: Minimum, installed in air ducts
Energy savings: $34,000 per year
Payback: 4-5 years
Indoor air must be constantly renewed to maintain adequate occupancy conditions. However, there is an energy cost when outdoor air replaces indoor air.
- During the summer, the intake air is usually hotter and more humid than the exhaust air.
- The opposite happens during winter : the intake air is colder and drier.
Some energy can be saved by exchanging heat and moisture between both airflows, reducing HVAC load. This concept is called energy recovery ventilation and there are two types : food recovery ventilation (HRV) exchanges only heat, while enthalpy recovery ventilation (ERV) exchanges heat and moisture.
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1) Meet the same heating and cooling loads with lower HVAC operating costs. 2) Savings on electricity and gas. |
1) Effective only under certain weather conditions. 2) Maintenance becomes more complex. |
14. Low-flow hydraulic installations
Exotic Level: 1/5
Cost: $90,000
Space requirement: Without additional space, they replace existing equipment
Energy savings: $13,500 per year
Payback: 7-10 years
Conserving water not only reduces the corresponding bill, but also the operating cost of the hot water system. The U.S. Environmental Protection Agency administers the WaterSense labeling program, which promotes the use of low-flow plumbing fixtures .
A quick way to reduce water consumption is to upgrade your plumbing to its efficient versions. Furthermore, there is no need to modify pipes embedded in walls or slabs.
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1) Reduction in water bills and heating expenses. 2) There are also savings in pumping if the building has a booster pump. |
1) If the existing fittings and piping are very old, the replacement procedure may damage the piping. |
15. Wind Microturbine
Exotic Level: 5/5
Cost: $400,000 for a 100 kW turbine installed ($296,000 after federal tax credit)
Space Requirement: 3,000 – 4,000 square feet of clear space around the turbine
Energy savings: $43,800 per year
Payback: 7-10 years
While solar panels are easier to install and maintain, wind energy can be cost-effective if your site has the right conditions. As a renewable energy source, wind energy also benefits from incentives.
Most properties do not have enough space for a large-scale wind turbine. However, it makes sense to use one larger drive instead of many smaller drives:
- A single turbine results in lower cost per kilowatt (economies of scale).
- Electricity generation is improved with a taller tower since the airflow is more stable as the height increases.
- On the other hand, smaller turbines are close to the ground and susceptible to turbulence caused by trees and buildings.
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1) Electricity savings, zero generation cost after payback period. 2) May be eligible for incentives from the government or utility companies. 3) Wind energy complements solar energy, as it depends on a different energy input. |
1) Demanding in terms of site conditions. Not all properties are suitable for wind energy. 2) Neighbors may be concerned about noise or visual impact. 3) More complex maintenance than solar energy. |
16. HEPA Air Filtration
Exotic Level: 3/5
Cost: $45,000
Space Requirement: 30% larger filter housings on any external air intake
Energy saving: Not applicable, as the objective is to improve air quality.
Return: Not applicable.
HEPA stands for high-efficiency particulate air or high-efficiency particle retention. These filters are highly effective, capturing 99.97% of particles 0.3 microns in size or larger. They can remove germs and pollutants from the air, improving indoor air quality.
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1) Simple to install and compatible with many types of HVAC equipment. 2) Contributes to the health of occupants by removing harmful particles. |
1) It causes a slight increase in the required fan power, as the filter itself causes a drop in air pressure. |
17. Change of peak electrical load
Exotic Level: 4/5
Cost: $200,000
Space Requirement: 5' x 5' for a 100 kW system
Energy savings: $24,000 per year
Payback: 8-9 years
Depending on how your energy bill is structured, changing your electrical load can reduce your billed amount, even if your total kilowatt-hour consumption remains the same.
- Some electricity tariffs were priced higher per kWh during peak demand hours. If this is your case, your energy bill can be reduced by shifting consumption to off-peak times.
- Large consumers are charged the highest measured demand in the billing period , regardless of when it occurs. In these cases, demand must be continuously monitored to avoid consumption spikes.
There are many ways to reduce demand spikes. Loads that are not time-sensitive can simply be turned off and energy storage systems can help power the necessary loads. Please note that electricity consumption peaks are not billed if they are supplied with internal energy resources:
- Batteries can be used to power electrical loads.
- Ice storage can be used to cool, shut down refrigeration and air conditioning systems during peak demand times.
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1) Reduce electricity bills, even if total energy consumption remains the same. 2) Peak shaving systems can also often be used as energy storage. |
1) Only possible with certain rates. Load shifting only provides savings when there are time-of-day rates or peak demand charges. |
18. CO2-controlled ventilation
Exotic Level: 3/5
Cost: $233,000
Space requirement: Minimal, involves adding compact sensors and control devices
Energy savings: $47,500 per year
Payback: 4-5 years
Ventilation systems are typically designed based on two values: the square footage and the number of occupants. This means that total airflow in cubic feet per minute (cfm) is based on cfm/sf and cfm/person. However, many ventilation systems maintain maximum airflow even when the area served is not full, which represents a waste of energy.
As human metabolism produces carbon dioxide, occupancy can be correlated with the concentration of CO2 in the air. Ventilation can be controlled with CO2 sensors, reducing airflow based on occupancy to save energy.
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1) Reduction in electricity consumption of ventilation systems. 2) Indoor air quality is not affected as the projected airflow per person is maintained. |
1) Higher initial cost compared to a conventional ventilation system. 2) Control devices cause some distortion in the power supply (harmonics). |
19. Economizer Mode for Air Conditioning
Exotic Level: 3/5
Cost: $50,000
Space Requirement: Doubles the size of each air handler with ducts and controls
Energy savings: $19,500 per year
Payback: 2-3 years
In some climate zones, weather conditions are suitable for “free air conditioning” during some times of the year. In these cases, a constant supply of outside air has the same effect as air conditioning and compressors can be turned off to save energy. Although there is an increase in fan power, the savings on air cooling are much greater.
This mode of operation is available when the HVAC system has an airside economizer. In some jurisdictions, including New York, economizers are required by the energy code.
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1) Saves electricity by reducing air conditioning operating time. 2) Indoor air quality is not affected. |
1) Additional expenses: initial cost and maintenance. 2) Not suitable for all climate zones. |
20. Variable frequency drives in fans and pumps
Exotic Level: 3/5
Cost: $38,850
Space requirement: Minimal, most are smaller than a residential distribution board
Energy savings: $16,000 per year
Payback: 2-3 years
Variable frequency drives are electronic devices that adjust the voltage and frequency supplied to motors, reducing the speed below their rated rpm. VFDs are very useful in fans and pumps, as these devices are often subject to partial load. VFDs are also known as variable speed drives or VSDs.
When the full power of a pump or fan is not required, two control strategies are common:
- Pump water flow (gpm) can be controlled with a series valve on the discharge.
- Alternatively, a fan's average airflow (cfm) can be controlled with intermittent operation. For example, to achieve an average airflow of 800 cfm with a 1000 cfm fan, it can run 80% of the time.
When using a VFD on a pump, the discharge valve can be fully opened to eliminate power loss due to pressure drop. For fans, reducing speed saves much more energy than reducing run time – a fan running at 80% speed uses less electricity than a fan running at full speed 80% of the time.
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1) Saving ventilation and pumping. 2) Synergy with other energy efficiency measures, such as CO2-based ventilation control. |
1) It offers no benefit on engines that must operate at rated speed all the time. 2) Slight power supply distortion (harmonics). |
Conclusion
Green building is a broad topic and there are many design resources available to building owners. Depending on project conditions, some measures may achieve better results than others. However, green building is a proven way to save energy and water while reducing the environmental impact of cities.
