2724 Cost Reduction Strategies

M&V strategies can be cost reduced by lowering the requirements for M&V or by statistical sampling. Reducing requirements involves performing trade-offs with the risks and benefits of having reliable numbers to determine the savings and the costs for these measurements.

27.2.4.1 Constant Load ECMs

Lighting ECMs can save 30% of the pre-ECM energy and have a payback in the range of 3 to 6 years. Assuming that the lighting ECM was designed and implemented per the specifications and the savings were verified to be occurring, just verifying that the storeroom has the correct ballasts and lamps may constitute acceptable M&V on a yearly basis. This costs far less than performing a yearly set of measurements, analyzing them and then creating reports. In this case, other safeguards should be implemented to assure that the bulb and ballast replacement occurs and meets the

Figure 27.22: Cumulative Impact of Savings Loss.

Figure 27.21: Yearly Impact of Ongoing Losses.

Figure 27.22: Cumulative Impact of Savings Loss.

requirements specified.

High efficiency motor replacements provide another example of constant load ECMs. The key short term risks with motor replacements involve installing the right motor with all mechanical linkages and electrical components installed correctly. Once verified, the long term risks for maintaining savings occur when the motor fails. The replacement motor must be the correct motor or savings can be lost. A sampled inspection reduces this risk. Make sure to inspect all motors at least once every five (5) years.

27.2.4.2 Major Mechanical Systems

Boilers, chillers, air handler units, cooling towers comprise the category of manor mechanical equipment in buildings. They need to be considered separately as each carry their own set of short-term and long-term risks. In general, measurements provide necessary risk reduction. The question becomes: What measurements reduce the risk of savings loss by an acceptable amount?

First a risk assessment needs to be performed. The short-term risks for boilers involve installing the wrong size or installing the boiler improperly (not to specifications). Long-term savings sustainability risks tend to focus on the water side and the fire side. Water deposits (K+, Ca++, Mg+) will form on the inside of the tubes and add a thermal barrier to the heat flow. The fire side can add a layer of soot if the O2 level drops too low. Either of these reduce the efficiency of the boiler over the long haul. Generally this can take several years to impact the efficiency if regular tune-ups and water treatment occurs.

Boilers come in a wide variety of shapes and sizes. Boiler size can be used as a defining criterion for measurements. Assume that natural gas or other boiler fuels cost about $5.00 per MMBtu. Although fuel price constantly changes, it provides a reference point for this analysis. Thus a boiler with IMMBtu per hour output, an efficiency of 80% and operating at 50% load 3500 hours per year, consumes about $11,000 per year. If this boiler replaced a less efficient boiler, say at 65%, then the net savings amounts to about $2,500 per year, assuming the same load from the building. At 5% of the savings, $125 per year can be used for M&V. This does not allow much M&V. At 10% of the annual savings, $250 per year can be used. At this level of cost, a combustion efficiency measurement could be performed, either yearly or bi-yearly, depending on the local costs. In 2003 the ASME's Power Test Code 4.1 (PTC-4.1)185 was replaced with PTC4. Either of these codes allows two methods to measuring boiler efficiency. The first method uses the energy in equals energy out—using the first law of thermodynamics. This requires measuring the Btu input via the gas flow and the Btu output via the steam (or water) flow and temperatures. The second method measures the energy loss due to the content and temperature of the exhausted gases, radiated energy from the shell and piping and other loss terms (like blowdown). The energy loss method can be performed in less than a couple of hours. The technician performing these measurements must be skilled or significant errors will result in the calculated efficiency. The equation below shows the calculations required.

Efficiency = 100% - Losses + Credits

The losses term includes the temperature of the exhaust gas and a measure of the unburned hydrocarbons by measuring CO2 or O2 levels, the loss due to excess CO and a radiated term. Credits seldom occur but could arise from solar heating the makeup water or similar contributions. The Greek letter "n" usually denotes efficiency.

As with boilers, a risk assessment needs to be performed for chilers. The short term risks for chillers involve sizing or improper installation. Long term savings sustainability risks focus on the condenser water system, as circulation occurs in an open system. Water deposits (K+, Ca++, Mg+, organics) will form on the inside of the condenser tubes and add a barrier to the thermal flow. These reduce the efficiency of the chiller over the long haul. Generally this can take several years to impact the efficiency if proper water treatment occurs. Depending on the environmental conditions, the quality of the makeup water and the water treatment, condenser tube fouling should be checked every year or at least every other year.

Chillers consume electricity in the case of most centrifugal, screw, scroll and reciprocating compressors. Direct-fired absorbers and engine driven compressors use a petroleum based fuel. As with boilers, chiller size and application sets the basic energy consumption levels. Assume, for the purpose of this example, that electricity provides the chiller energy. Older chillers with water towers often operate at the 0.8 to 1.3 kW per ton level of efficiency. New chillers with water towers can operate in the 0.55 to 0.7 range of efficiency. Note that the efficiency of any chiller depends upon the specific operating conditions. Also assume the following: 500 Tons centrifugal chiller with the specifications shown in Table 27.20. Under these conditions the chiller produces 400 Tons of chilled water and requires an expenditure of $ 38,000 per year, considering both energy use and demand charges. Some utilities only charge demand charges on the transmission and delivery (T&D) parts of the rate structure. In that case, the cost at $0.06/kWh would be closer to $28,000. Using the 5% (10%) guideline for M&V costs as a percentage of savings leaves almost $1,100 ($2,200) per year to spend on M&V. This creates an allowable expenditure over a 20-year project of $22,000 ($44,000) for M&V. If the utility has a ratchet clause in the rate structure, the amount for M&V increases to $1,700 ($3,400) per year. At $1,100 per year, trade-offs will need to be made to stay within that "budget." The risks need to be weighed and decisions made as to what level of M&V costs will be allowed.

To determine the actual efficiency of a chiller requires accurate measurements of the chilled water flow, the difference between the chilled water supply and return temperatures and the electrical power provided to the chiller. Costs can be reduced using an EMCS if only temperature, flow and power sensors need to be installed.

Cooling tower replacement requires knowledge of the risks and costs involved. As with boilers and chillers, the primary risks involve the water treatment. Controls can be used to improve the efficiency of a chiller/tower combination by as much as 15% to 20%. As has been previously stated, control ECMs often get overridden and the savings disappear.

27.2.4.3 Control Systems

Control ECMs encompass a wide spectrum of capabilities and costs. Upgrading a pneumatic control system and installing EP (electronic to pneumatic) transducers involves the simple end. The complex side could span installing a complete EMCS with sophisticated controls, with various reset, pressurization and control strategies. Generally, EMCSs function as basic controls and do not get widely used in sophisticated applications.

Savings due to EMCS controls bear high sustainability risks. When an operator overrides a strategy and forgets to re-enable it, the savings disappear. A common EMCS ECM requires the installation of equipment and programs used to set back temperatures or turn off equipment. Short term risks involve setting up the controls so that performance enhances, or at least does not degrade, the comfort of the occupants. When discomfort occurs, either occupants set up "portable electric reheat units" or operators override the control program. For example, when the night set-back control does not get the space to comfort by occupancy, operators typically override instead of adjusting the parameters in the program. These actions tend to occur during peak loading times and then not get re-enabled during milder times. Long term risks cover the same area as short term risks. A new operator or a failure in remote equipment that does not get fixed will likely cause the loss of savings. Estimating the savings cost for various projects can be done when the specifics are known.

Table 27.21: Sampling Requirements.

Precision

20%

20%

10%

Confidence

80%

90%

90%

0 0

Post a comment