There is a common misconception that green building design means assuming higher costs to protect the environment. In reality, green design is an excellent business decision: it lowers the ownership cost of a building over its lifetime, while reducing its environmental footprint. In addition, green construction raises the image of developers as corporate citizens, attracting tenants who consider sustainability a top priority.
This article will describe 20 green design features that can be added to buildings, reducing emissions and waste while achieving an attractive return on investment. For each green design feature described, general information is provided on cost, size, savings and payback period. Note these are broad estimates, which may change depending on the specific conditions of each project.
The performance of each green design features will be described based on a 100,000 sq. ft. apartment with the following characteristics:
The total building energy expense (gas, electricity and water) is $42,600/month, or $511,200/year.
Exotic Level: 5 / 5 Cost: $1.4M (200 kW microturbine, $3,000/kW material cost, $7,000/kW total installed cost) Space Requirement: 400 sf room Energy Savings: $195,000 / year Payback: 7-8 years
Cogeneration is also known as combined heat and power (CHP), and it consists on producing electricity and heat simultaneously. Many electricity generation methods release heat as a secondary product, which is normally wasted. However, it can be recovered and used for space heating, domestic hot water and many industrial processes.
Cogeneration equipment can be classified into two main types: microturbines and reciprocating engines. Both rely on natural gas combustion to drive the generator, and waste heat is recovered from engine cooling water and exhaust gases.
1) Lower electricity and heating expenses, compared with relying 100% on utility services.
2) The cogeneration system can be used as an emergency generator, combining two pieces of equipment in one.
1) Complex and expensive system.
2) Only viable in occupancies with a high demand for hot water, where waste heat can be used continuously. If this is not the case, using the electric utility service is cheaper.
Some examples of occupancies where cogeneration is viable are hotels and hospitals. It is also possible to drive an absorption chiller with waste heat, deploying a concept called trigeneration: simultaneous electricity generation, heating and cooling.
2. Fuel Cells
Exotic Level: 5 / 5 Cost: $2M normally, $1.4M after 30% federal tax credit (200 kW unit, $8000/kW material cost, total installed cost $10,000/kW) Space Requirement: Typically less than 200 sq. ft. Energy Savings: $180,000/year Payback: 7-8 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 more cost-effective when both the heat and electricity output can be used continuously.
Unlike batteries, which contain the reagents that produce electricity, fuel cells use an external source and cannot be “discharged”. The reaction can continue indefinitely as long as the reagents are supplied.
1) Compact and lightweight.
2) Some types can be used for energy storage, complementing renewable power systems with variable output (solar panels and wind turbines).
1) Financial viability can be affected if the price of the input fuel becomes volatile.
2) Maintenance is complex and requires specialized labor.
There are many fuel cell compositions, and two emerging types are especially promising: solid oxide fuel cells (SOFC) and hydrogen fuel cells. The Bloom Energy Server is an example of a commercially successful SOFC, which has been deployed by tech giants such as Google, Yahoo and eBay.
3. Solar Photovoltaic Panels
Exotic Level: 3 / 5 Cost: $400,000 for a 120kW system (around $250,000 after incentives) Space Requirement: Around 10,000 sq. ft. of rooftop area (12W/sf roof area) Energy Savings: $44,000 per year Payback: 5-6 years
Solar power systems are among the most promising building upgrades if you have plenty of rooftop area available. They normally come with a 10-year warranty for manufacturing defects and a 25-year warranty for energy generation, in addition to having simple maintenance needs.
Both New York and New Jersey offer incentive for solar panels, including rebates and tax breaks. There is also a nationwide federal tax credit program, where 30% of the cost of solar power systems is deductible from your federal tax burden. Also consider that both states have very expensive electricity, increasing the value of generating your own kilowatt-hours.
The Tesla solar roof is a promising innovation in solar photovoltaics, which basically integrates solar cells into roof shingles. The concept can be expensive in existing buildings, since you have to replace the whole roof, but it becomes promising in new constructions - there is a roofing cost to assume anyway.
1) The payback period of solar panels only represents a small fraction of their service life. Your ROI is assured thanks to the warranty.
2) Simple maintenance. The main requirement is keeping panel surfaces clean and free of shadows.
3) May be eligible for incentives from the government or utility companies.
1) Power generation depends on sunlight. It ceases at night and is reduced drastically under cloudy weather.
2) Finding space may be a limitation in some buildings, due to Fire Department clearances and rooftop mechanical equipment.
4. Solar Thermal Collectors
Exotic Level: 2 / 5 Cost: $200,000 ($2,000 per dwelling), $140,000 after 30% federal tax credit Space Requirement: 10,000 sq. ft. of rooftop area (same as solar panels) Energy Savings: $20,000 per year Payback: 7 years
Great alternative to photovoltaic panels for a smaller first cost. Like photovoltaic panels, solar thermal collectors also harness sunlight. However, solar radiation is used directly for domestic hot water instead of electricity generation. With this building upgrade, you can rely less on your gas-fired water heater. There may be a slight pumping cost in taller buildings, since water has to reach the rooftop, but it is much less than the ongoing cost of a water heater.
1) Financially viable: Offers free heating when sunlight is available.
2) Simple installation and maintenance.
1) No heating at night and limited effectiveness in the winter. You need another heating system as backup.
2) Competes with solar photovoltaics for rooftop area. If space is a limitation, solar panels tend to offer a better ROI.
5. Central Chiller Plant
Exotic Level: 3 / 5 Cost: $2M Space Requirement: 1500 sq.ft. 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 a cooling tower. Modern units are equipped with artificial intelligence, and can adjust their cooling output to match building load.
Chiller plants achieve significant economies of scale, consolidating air conditioning compressors in a single location, and making sure they as efficient as possible. Building cooling is achieved with hydronic piping and fan-coils, and the system becomes even more efficient if the pumps and fans are controlled by VFDs.
1) Chiller plants provide one of the most efficient air conditioning configurations.
2) Synergy with other energy efficiency measures such as VFDs in pumps and fans.
1) High upfront cost and requires a dedicated area for the chillers and their complementary systems.
2) A centralized configuration means the entire building can be left without AC if a key system component fails.
6. Geothermal Heating and Cooling
Exotic Level: 4 / 5 Cost: $3.3M, $2.31M after federal tax credit ($10,000 per ton of capacity, 300 sf/ton, 1 well per ton, 333 tons for this building) Space Requirement: Same as a conventional chiller, boiler or furnace Energy Savings: $105,000 per year Payback: 18-25 years
The underground is an excellent heat sink in summer and an excellent heat source in winter. Geothermal heat pumps take advantage of this, providing heating and cooling for buildings with a lower kWh consumption than other methods.
Indoor heating and cooling are provided normally with hydronic piping, air-handling units and air ducts.
The geothermal heat pump uses a secondary piping circuit that goes underground, to collect or reject heat as needed.
1) Geothermal heat pumps are among the most efficient heating and cooling systems for building interiors.
2) Can provide heating for the same cost as natural gas (or even less), while eliminating the associated emissions.
3) The well field eliminates the need for a 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 ft deep wells of pipe in lieu of a simple cooling tower and boiler is a much more costly alternative.
4) If cooling and heating loads aren’t balanced and small cooling tower or boiler may still be required.
5) Geothermal wells must be spaced about 15’ apart, so a well field to handle this building is approximately 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 collected rainwater for decades, but the concept has gained more importance in the modern world, especially in places affected by water shortage. In simple terms, rainwater harvesting requires a collection method and a storage system, and all the rainwater retained is subtracted from what you would normally consume from the municipal supply.
In densely populated areas like NYC, rainwater harvesting also reduces the water volume handled by sewage pipes during a storm, helping prevent spillage. A single building with rainwater harvesting does not have a major impact, but the rainwater retention effect adds up after many property owners have deployed it.
1) Free water supply.
2) Decongests public sewage during major storms. Retrofitting existing properties with rainwater harvesting is relatively simple.
1) Does not provide a consistent water supply throughout the year, since it depends on rainfall.
8. Greywater/Blackwater Recycling
Exotic Level: 4 / 5 Cost: $200,000 ($2,000 per dwelling) Space Requirement:One 250 gal tank per dwelling, 36” diameter and 66” height Water Savings: $20,000 Payback: 10-12 years
The concepts of greywater and blackwater are used to describe water that has already been used in plumbing fixtures. Blackwater includes water from all fixtures, while greywater excludes the water discharged from toilets.
Although greywater is polluted with cleaning agents and grease, it can be collected and reused for purposes such as flushing toilets or outdoor watering. Blackwater can also be recycled for some purposes, but it requires special treatment.
1) Reduced water bills: Less water is drawn from the municipal supply when the same water is used for various purposes.
2) Decongestion of public sewage.
1) May not be practical in existing properties where greywater is not separated from blackwater.
2) Blackwater recycling requires an expensive treatment system.
Greywater and blackwater separation is easier in new constructions where the plumbing system has not been installed. Water recycling is more challenging in existing buildings, where the water from all plumbing fixtures is combined, and only blackwater is available.
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 short payback period and a long service life. In addition, lighting savings are subtracted from your space cooling load, which leads to air conditioning savings. LED lamps also offer a much longer service life than incandescent, fluorescent and HID lamps, which means replacements are much less frequent.
1) Significant electricity savings: Over 30% less power consumption than fluorescent, over 50% less than HID, and over 80% less than incandescent.
2) Reduced cooling load for AC and refrigeration equipment.
3) Long service life and almost no maintenance is required.
1) High upfront cost.
2) Some people prefer the warm glow of incandescent or halogen lights, although this can be solved by using LEDs that mimic them.
Exotic Level: 3 / 5 Cost: $10,000 for five skylights in the upper floor Space Requirement: No additional space Energy Savings: $2600 per year Payback: 3-4 years
LEDs provide lighting for a low cost, but only light from the sun is free. Daylighting consists on maximizing the use of sunlight indoors, while preventing its two negative effects:
Glare, 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 positioning, and skylights can be used in single-story constructions or the upper levels of multi-story buildings.
1) Free lighting.
2) Windows and skylights have very simple maintenance requirements.
1) Potential for glare and unwanted solar heating.
2) Unavailable at night.
11. Occupancy-Sensing Lighting Controls
Exotic Level: 2 / 5 Cost: $4,500 for 30 sensors throughout the building ($150 each) Space Requirement: Minimal, same size as smoke detectors and wall switches Energy Savings: $5,250 per year Payback: Less than one year
LED lighting upgrades often have a rebound effect: since occupants are aware that lighting is more efficient, they may become careless and leave the lights on more frequently. Occupancy sensors can be used to solve this problem, making sure the lights are only on when needed.
1) Synergy with LED lighting, enhancing the savings achieved.
2) Occupants don’t have to worry about switching the 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 further 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 overall building cost, $3.62M for a 100,000 sq.ft. construction Space Requirement: Building size is not affected Energy Savings: $333,000 per year Payback: 10-15 years
The concept of Passive House construction originally comes from Germany (Passivhaus), but it applies for all types of buildings despite having the word “house” in its name. Passive house construction is based on maximizing natural ventilation and using high-performance insulation to reduce HVAC expenses significantly or eliminate them completely.
Passive house construction also optimizes the solar heating effect, preventing it during summer and maximizing it during winter. Any HVAC equipment used is combined with energy recovery measures, to further reduce operating costs.
1) Significant energy savings, may exceed 75% compared with a conventional building.
2) Exceeds energy code performance in both NY and NJ.
1) More expensive building by 5-10%.
2) Limited application in existing constructions, since the envelope has already been built.
13. Energy Recovery Ventilation
Exotic Level: 3 / 5 Cost: $150,000 ($1,500 per dwelling) Space Requirement: Minimal, installed on air ducts Energy Savings: $34,000 per year Payback: 4-5 years
Indoor air must be replenished constantly to maintain adequate conditions for occupancy. However, the exhaust air hides a waste of energy:
During summer, intake air is often warmer and moister than exhaust air.
The opposite happens during winter: intake air is cooler and drier.
Energy can be saved by exchanging heat and moisture between both airstreams, reducing the load on HVAC equipment. There are two types of energy recovery ventilation:
Heat-recovery ventilation (HRV) only exchanges heat.
Enthalpy-recovery ventilation (ERV) exchanges both heat and moisture.
1) Meeting the same heating and cooling loads with lower HVAC running costs.
2) Electricity and gas savings.
1) Only effective under certain weather conditions.
2) Maintenance becomes more complex.
14. Low-Flow Plumbing Fixtures
Exotic Level: 1 / 5 Cost: $90,000 Space Requirement: No additional space, they replace existing fixtures Energy Savings: $13,500 per year Payback: 7-10 years
Saving water not only reduces the water bill; you can also expect lower operating costs from the domestic hot water system. The US Environmental Protection Agency manages the WaterSense labeling program, which promotes the use of low-flow plumbing fixtures.
Upgrading conventional plumbing fixtures to their efficient versions provides a quick way to reduce water consumption. There is no need to modify the piping embedded in walls or floors.
1) Reducing water bills and heating expenses.
2) There are also pumping savings if the building relies on a booster pump.
1) If the existing fixtures and piping are very old, the replacement procedure may damage piping.
15. Micro Wind Turbine
Exotic Level: 5 / 5 Cost: $400,000 for a 100 kW turbine installed ($300,000 after incentives) Space Requirement: 3,000 - 4,000 sq. ft. of clearance around the turbine Energy Savings: $43,800 per year Payback: 7-10 years
Although solar power systems are easier to install and service, wind power can also be cost-effective if your site has the right conditions. Being a renewable energy source, wind power also benefits from incentives.
Most properties do not have enough space for a utility-scale wind turbine. However, it makes sense to use one large unit instead of multiple smaller units:
A single turbine results in a lower cost per kilowatt.
Electricity generation is enhanced with a taller tower, since airflow is more stable as height increases. Smaller turbines are closer to the ground and susceptible to the turbulence caused by trees and constructions.
1) Electricity savings, zero generation cost after the payback period.
2) May be eligible for incentives from the government or utility companies.
3) Wind power complements solar power, since it depends on a different energy input.
1) Demanding in terms of site conditions. Not all properties are suitable for wind power.
2) Neighbors may be concerned about noise or visual impact.
3) More complex maintenance than solar power.
16. HEPA Air Filtration
Exotic Level: 3 / 5 Cost: $45,000 Space Requirement: 30% larger filter boxes on any outside air intakes Energy Savings: Does not apply, since the purpose is improving air quality. Payback: Does not apply.
HEPA stands for high efficiency particulate arrestance or high efficiency particulate arrestance. HEPA filters are among the best available, capturing 99.97% of particles with a size of 0.3 microns or more. These filters remove many pollutants and allergens from the air, improving indoor air quality.
1) Simple to install and compatible with many types of HVAC equipment.
2) Contributes to occupant health by removing harmful particles.
1) Causes a slight increase in the fan power required, since the filter itself causes an air pressure drop.
17. Peak Electric Load Shifting
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 power bill is structured, you may be able to reduce consumption even if the total number of kilowatt-hour stays the same.
Some electricity tariffs have a higher kilowatt-hour price during peak demand hours. If this is your case, the power bill can be reduced by moving consumption from peak hours to off-peak hours.
Large consumers are normally charged for the highest demand measured in the billing period, regardless of when it occurs. In this case, demand must be constantly monitored to prevent peaks.
There are many ways to trim peak demand. Loads that are not time-sensitive can simply be turned off, and energy storage can be used to power loads that are necessary. Note that peaks in demand are not billed if they are covered with internal energy resources:
Batteries can be used to power electric loads.
Ice storage can be used for cooling loads, turning off refrigeration and AC equipment during peak demand hours.
1) Reducing electricity bills, even if total energy consumption stays the same.
2) Peak shaving systems can often be used as energy storage as well.
1) Only possible with certain tariffs. 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 normally designed based on two values: square footage and the number of occupants. This means that total airflow in cubic feet per minute (cfm) is based on cfm/sq.ft. and cfm/person. However, many ventilation systems keep the maximum design airflow even when the area is not at full occupancy, and this represents a waste of power.
Since the human metabolism produces carbon dioxide, occupancy can be correlated with the CO2 concentration in the air. Ventilation can be controlled with CO2 sensors, reducing airflow in proportion to occupancy to achieve energy savings.
1) Reducing electricity consumption from ventilation systems.
2) Indoor air quality is not affected, since the design airflow per person is maintained.
1) Higher upfront cost compared with a conventional ventilation system.
2) Control devices cause some distortion of the power supply (harmonics).
19. Economizer Mode for Air Conditioners
Exotic Level: 3 / 5 Cost: $50,000 Space Requirement: Doubles size of each air handler with ducting and controls Energy Savings: $19,500 per year Payback: 2-3 years
In certain climate zones, weather conditions are sometimes suitable for “free air conditioning”, where a constant supply of outdoor air is enough to meet the cooling load. In these cases, air conditioning compressors can be turned off to achieve significant energy savings. This operation mode is available when HVAC systems are equipped with an airside economizer. In NYC and many other jurisdictions, economizers are required per local energy code.
1) Achieves power bill savings by reducing AC compressor runtime.
2) Indoor air quality is not affected.
1) Additional expenses in upfront cost and maintenance.
2) Not suitable for all climate zones.
20. Variable Speed Drives on 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 speed drives are device that modify the voltage and frequency supplied to a motor, allowing it to operate below rated rpm. VSDs are very useful in motors that drive fans and pumps, since these devices are often subject to part-load conditions. They are also known as variable frequency drives (VFD).
When the full output of a pump or fan is not required, the most common control strategies are the following:
The water flow provided by a pump (gpm) is controlled with a series valve at the pump discharge.
The average airflow from a fan (cfm) is controlled through intermittent operation. For example, to achieve an average airflow of 800 cfm with a 1000 cfm fan, it only operates 80% of the time.
Using a VFD in a pump allows the valve to be fully opened, eliminating the power loss produced by the pressure drop. For fans, reducing speed saves much more energy than reducing the time of operation - a fan at 80% speed consumes much less electricity than a full-speed fan running 80% of the time.
1) Saving on ventilation and pumping.
2) Synergy with other energy efficiency measures such as CO2-based ventilation control.
1) Provides no benefit in motors that must operate at rated speed all the time.
2) Slight distortion of the power supply (harmonics).
At Nearby EngineersNew York EngineersMintropy, we search for simple, eloquent solutions to complex problems. We minimize construction costs by eliminating the extraneous and focusing on the overall efficiency for the most streamlined designs.