By Randy Niederer, LEED AP
As an initiative of the U.S. Department of Energy (DOE), the Better Buildings Alliance (BBA) is designed to improve the efficiency of commercial and industrial buildings in the United States by driving leadership in energy innovation. The commercial buildings sector consumes nearly 20% of all energy used in the U.S., and 15% of that total floor space is comprised of warehouses and distribution centers (see Figure 1). Much of this energy, both electricity and natural gas, is wasted because of inefficient or outdated technology. Energy efficient technologies, if installed, commissioned, and operated properly are a cost-effective way to save money and reduce pollution.
Member organizations of the BBA have been working with the DOE to develop and adopt innovative, cost-effective, energy-saving solutions measures to reduce energy consumption across all sectors of the commercial market.
Unit heaters, a traditional method of providing heat in large spaces, are found in commercial and industrial buildings throughout the U.S. These appear most prominently in warehouses, distribution centers, loading docks, etc. In addition to space heating, these same buildings require ventilation systems to meet minimum ventilation rates required by code. A challenge faced with unit heaters is that they are highly inefficient. Also, for most applications separate systems are used for space heating and outside air (as required by ASHRAE 90.1), adding project complexity and energy consumption.
Conversely, High Temperature Heating & Ventilation (HTHV), a classification of heating products created by the DOE with the goal of increasing energy efficiency in heating, have been documented as being 20% more efficient than unit heaters. HTHV products provide a discharge temperature equal to or greater than 150° F and an overall temperature rise equal to or greater than 140°F. This technology is used to provide both space heating and ventilation for large commercial and industrial spaces.
In 2013, a field study conducted by the DOE compared the natural gas usage between HTHV space heaters and unit heaters in a 42,000 square foot warehouse in Bridgeton, MO. In a side-by-side comparison of alternating months over the 2013-14 heating season, the HTHV direct-fired natural gas heaters consumed 20% less natural gas than the existing heaters on a normalized basis over the monitoring period (see Figure 2). This value exceeded the expected energy savings values of 11% from thermal efficiency of >90% vs. standard efficiency of 80% for gravity-vent units.
HTHV heaters operate with a powerful, high-pressure supply fan to deliver the heated air to the floor and create vertical circulation that can reduce temperature stratification between the floor and ceiling and can also be used to deliver outside air requirements for the building.
While this strategy reduces thermal energy consumption, the units carry higher fan electricity consumption, which offsets a portion of the thermal savings. Nevertheless, over an average heating season for the host site in Bridgeton, MO (3,705 average HDD [heating degree day]—60°F [16°C]), the new natural gas heaters would save approximately 15% on space heating utility costs at average utility rates for the site of $0.8/therm and $0.08/kWh.
The HTHV showed improved temperature control over the traditional equipment by reducing thermal stratification between the floor and ceiling. Figure 3 displays the difference in temperature near the floor (5′ above the floor) and at the ceiling (20′ above the floor) during the monitoring period.
For buildings with high ceilings, such as the warehouse in this demonstration, warm air naturally rises and can raise the average ceiling air temperature Δ10-20°F (Δ6-11°C) above the thermostat set point. Because of this temperature gradient, the heating system must run longer and consume more energy to meet the needs of the building’s occupants at or near floor level. As demonstrated by the temperature differential between floor and ceiling in Figure 3, the HTHV gas heaters eliminate much of the temperature stratification experienced with the existing unit heaters. Generally, the existing gas heaters exhibited vertical temperature differences of more than Δ5°F (Δ3°C) higher than exhibited by the high-efficiency gas heaters. HTHV direct-fired gas heaters and other destratification technologies increase air circulation and provide more uniform temperature distribution throughout the space.
Additionally, because the roof is typically the largest area for heat transfer in a warehouse, lowering the temperature of the interior ceiling decreases the heat loss through the roof.
The study concluded that “if deployed widely, high efficiency [HTHV] gas heaters would significantly decrease natural gas consumption related to space heating for semi-conditioned spaces such as warehouses, loading areas, distribution centers, etc. and manufacturing facilities.” In addition to the reduced natural gas consumption of direct-fired HTHV burners over standard unit heaters, natural gas savings can be achieved when HTHV is used in place of other heating solutions (e.g. boilers and gas furnaces).
Rebates And Tax Deductions For HTHV
An additional benefit facility managers can receive when purchasing and installing HTHV technology is a gas utility rebate. Both electric and natural gas utilities have offered rebates for energy efficient products that range from LED lighting to high efficiency direct gas fired HTHV equipment. For more than a decade, natural gas utilities across the country have been providing custom rebates for HTHV products through their commercial and industrial rebate programs.
Since the DOE has provided data via its study on HTHV equipment, a number of natural gas utilities are adding prescriptive rebates for HTHV products to their commercial and industrial programs. The prescriptive rebates amounts can vary by utility. Some utilities offer a set rebate amount for different Btu sizes available while others offer a $3.00 or $4.00 per thousand Btu rebate, which helps incentivize the purchase of even the largest heaters available. The latter rebates can provide as much as $12,800 in rebate funding for a 3.2 million Btu heater.
In addition, with the December 2015 extension of the EPAct, a law that provides 100% tax deductions for energy efficient products installed by owners of commercial buildings, a quicker equipment cost payback can be achieved. This tax extension applies retroactively to all energy efficient retrofits for 2015, as well as those installed through the end of 2016. These deductions and rebates, combined with the gas savings that a 92% efficiency that HTHV heater provides, can help drive down the return on investment that today’s facility owners and operators are seeking when purchasing capital equipment.
Young, J. 2014. Field Demonstration of High Efficiency Gas Heaters. Prepared for Better Buildings Alliance, Building Technologies Office, Office of Energy Efficiency, and Renewable Energy, U.S. Department of Energy.
Niederer is director of marketing for Cambridge Engineering, a manufacturer of industrial heating and ventilation systems. With 12 years of experience in the HVAC industry, part of his work involves working with utilities on next generation heating and ventilation technologies.
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