NOTE: www.kostic.niu.edu/ CHANGED TO www.niu.edu/kostic OR https://kostic.niu.edu
HVAC Energy and Utilities
Energy&Environment * EnergySTAR * Toyota PRIUS Myths, Facts, and Hype ... Additional Resources: Consumer’s Guide to Energy Efficiency * Alliance to Save Energy * American Council for an Energy-Efficient Economy * CEE* * Letter-hvac *HVAC-control**Johnson-Cs*tm9v*tc17*ecobee*Superheat-Subcool* eeba*EnergyCodes.gov * energy.gov...Energy-Saver (Heat-Pump Water-Heaters)
HVAC - Heating, Ventilation and Air Conditioning
An HVAC system, Heating (furnace), Ventilation (air ducts with filter and blower) and Air Conditioning (AC compressor with condenser and evaporator coil), to work efficiently and maintain desired comfort (temperature and humidity), first, it needs to be sized correctly. Second, the system needs to be installed and setup correctly. Finally, the system controls should be optimized to provide desired healthy comfort with maximum efficiency (fan speeds to be set or programed to deliver air flow about 350 for humid and 400 CFM/ton of cooling for dry climate, among others). The two-stage and modulated (variable multi-stage) HVAC systems with air fan's ECM (Electronically Commutated Motors) are more efficient (new ECM 80% over wide-range vs. old PSC 60% narrow-range) and adaptable to varying outdoor climate conditions (convenient programmatic control of speed/flow and torque/pressure/power, including feedback) to provide desired comfort and indoor air quality (temperature, humidity and air filtration) at high efficiencies.
For indoor humidity and comfort, it is better and more efficient to have a 'moderately undersized' than oversized Air Conditioning (AC) system.
Home Air Conditioning (AC) systems should maintain desirable and uniform, indoor temperature, and equally important, humidity comfort, about 75F temperature and 45% humidity. Ideally AC system should be working continuously without on/off interruptions to minimize humidity comfort oscillations and start-stop inefficiencies and equipment wear and tear. Since outdoor weather conditions are always changing to the extremes, then an AC system should provide accommodating, variable minimum-to-maximum cooling-power to minimize on-off oscillations of indoor air comfort. It also has to be powerful enough to provide indoor comfort for extreme weather conditions. It could be accomplished by variable speed and power of an AC compressor unit or rather frequent cycling-control of an AC one-stage compressor unit. The former, more complex system, may be prohibitively expensive and the latter with frequent start-stops is less efficient and with more equipment wear and tear, particularly if the AC system is oversized, as designers tend to do. If AC system is moderately undersized, it will provide better comfort most of the times, but during the rare, most extreme weather conditions, and it will be more efficient than an oversized AC system. During the most extreme weather conditions a moderately undersized AC system, while continuously working to achieve ideal comfort, it will provide more comforting, lower humidity with maximum possible outdoor-to-indoor temperature difference and pleasing comfort, even at moderately higher than desired indoor temperature. Therefore, moderately undersized AC system will provide better comfort at higher efficiency than an oversized system based on extreme whether conditions. A two-stage AC system (a low- and high-stage), if properly controlled to utilized low-power stage, is a good compromise between the more expensive, variable-speed (thus variable power) and less expensive basic, one-stage AC system. [Prof.MKostic.com]
Related: ECM in HVAC>Goof-Bad-Ugly*Glossary*Humidity&Fan speed*Ecobee multi-fan-speeds*LuxAire>AC&Furnace
Appliances: (see unit conversion below)
Typical furnace: 1 therm/h = 100,000 BTU/h = 29.3 kW(H) Heating power
Typical A/C unit: 3.5 tonR = 12.3 kW(C) Cooling power & minimum 13 SEER value (see below)
P[kW]=12Q[tonR]/SEER=12*3.5/13 = 3.2 kW(E) Electrical power
NOTE that in Chicago area climate a typical furnace heating-power is about 3 times bigger (about 30 kW) than A/C cooling-power (about 10 kW, corresponding to A/C compressor electrical power of about 3 kW depending on SEER value below, since the "relevant" outdoor-to-indoor temperature difference in winter (75-15) oF is about 3 times bigger than in summer (95-75) oF.
Energy Unit Conversion Calculator
1 therm = 100,000 BTU = 29.307 kWh
1 tonR = 12,000 BTU/h = 3.516 kW(C) Cooling (Refrigeration) power
1 SEER = (1 BTU)/Wh(E) = 1000 BTU/kWh [dimensional]= 0.293 kWh(C)/kWh(E)=0.293 [dimensionless], i.e., (cooling)/(electrical) energy-power ratio
What is EER and SEER? How does it apply to the energy efficiency of air conditioners?
Every air conditioning system has an efficiency rating known as its “Seasonal Energy Efficiency Ratio” (SEER). The SEER is defined as the total cooling (C) energy-output (in British-thermal-units or BTU) provided by an A/C system during its standardized annual usage period (for an average U.S. climate) divided by its total electrical (E) energy-input (in Watt-hours, Wh) during the same period. The actual “Energy Efficiency Ratio” (EER) is defined as the cooling (C) energy-output (in British thermal units or BTU) provided by an A/C system during its actual usage (for the specific outdoor air temperature of 95F and indoor temperature of 80F at 50% humidity) divided by its actual electrical (e) energy-input (in Watt-hours) during the same period. Actually dimensional EER is identical to dimensionless Coefficient-of-Performance (COP) of AC units used in Thermodynamics, i.e., 1 EER = (1 BTU)/Wh(E) = 0.294 kWh(C)/kWh(E)=0.294 COP dimensionless. The actual EER (or COP) varies with the outdoor-to-indoor temperature difference (season-averaged for SEER) and with specific design of the AC system (compressor size and its cycling efficiency, and size and efficiency of its condenser and evaporator heat-exchangers, i.e., super-heating and sub-cooling refrigerant temperatures, among others. The efficiency of an air conditioning systems is governed by U.S. law and regulated by the U.S. Department of Energy (DOE). The minimum SEER value was increased from 10 to 13 now, and EnergySTAR A/C systems have even higher values (SEER over 20). As compared to the seasonal-average AC efficiency, the actual efficiency for standard conditions (95F outdoor air and 80F indoor air at 50% humidity, i.e., 15F outdoor-to-indoor air temperature-difference) represents an actual Energy Efficiency Ration (1 EER=1BTU/W/h). Since standard 95F outdoor temperature is bigger than the typical seasonal-average outdoor air temperature, then the EER is smaller than SEER value for the same AC system, i.e., about 83% of SEER value. For example, a 13 SEER AC-system will have about 11 EER efficiency value (13*0.83).
What is a Ton of Refrigeration?
The cooling capacity of refrigeration units is traditionally indicated in "tons of refrigeration". One ton of refrigeration capacity rate (tonR) is equivalent to 12,000 BTU/h cooling rate. A ton of refrigeration (tonR) represents the thermal-heat energy transferred when a ton (2000 lb) of water at 32F freezes to ice during a 24-hour day. The refrigeration energy during the water freezing to ice is the latent heat of ice times the total weight. For example, a 3-ton(R) AC-unit will freeze 3 tons (6,000 lb) of chilled water to ice at 32 F in 24 hours.
Today, the cooling capacity of refrigeration units are often rated in BTU/h instead of ton(R). The BTU/h equivalent of one ton of refrigeration (tonR) is easy to calculate: multiply the weight of one ton of ice (2000 lb) by the latent heat of fusion (or melting) of ice (144 BTU/lb), and then divide by 24 hours to convert into BTU/h. Thus, one ton of refrigeration, 1 ton(R) = (2000X144)BTU/(24 h) = 12,000 BTU/h, or a 3-ton(R) AC-unit has 36,000 BTU/h cooling rate or thermal cooling-power.
Utilities [ComEd: www.ComEdCARE.com * www.ComEdservice.com (Electric Prices)]
NOTE: electricity cost in May '15, 2007?: $93.63/640 kWh=$0.15/kWh (Supply $51.67/640kWh=8.7 c/kWh); Sep.'14: $109.65/848kWh=$0.13/kWh; in August'08: $99.96/847kWh=$0.12/kWh); in Jan '07: $94.96/869kWh=$0.11/kWhr.
NiCorGas: www.nicorgas.com/gascost (Gas prices)
May '15 natural gas cost : $62.99/114.1=$0.55 c/therm; Jan '07 natural gas cost $96.53/116.7Therm=$0.827/Therm=$0.0282/kWhr (in the flier $0.67/Therm gas supply cost; see unit conversion below. NOTE, in August'08: $42.60/25.35Therms=$1.68/therm, about double Jan07-price per Therm);
NOTE, in Jan'07 the electricity was about 3.85 times more expensive than the gas energy above (in Aug'08 about 2 times), but considering the usual efficiencies the electrical heating cost would be about 3 times more (now about 50% more).