 I'm Ken Halivang, agricultural engineering specialist with the NDSU Extension Service and a professor in the agricultural and biosystems engineering department at North Dakota State University. The focus of this presentation is on a method of determining the energy efficiency of a grain dryer. Information that is needed to calculate the energy efficiency or consumption of a grain dryer includes the bushels of grain dried, the initial wet moisture content, the final dry moisture content, and the amount of fuel used. If a comparison is being made for the purchase of a new dryer, the purchase price of the new dryer or the cost to replace the existing dryer is needed and an estimate of the expected energy efficiency of the new dryer. Knowing about the existing system and typical performance of that type of system or dryer will help evaluate the accuracy of the calculated value. The dryer information may be on the internet, in the operator's manual, or you may need to obtain the information from the company. For example, the dryer in the picture is a NECO dryer and information can be found on their website. This shows the type of information normally included in the company brochure for the dryer. It lists the expected drying capacity and physical characteristics of the dryer. For example, the maximum burner output is listed as 4.5 million BTUs per hour. Typically, the operating heat requirement will be much less than the burner capacity. It also lists the total airflow for the blowers or fans. Note the many factors which affect the drying capacity, such as outside temperature and humidity, initial grain temperature, crop maturity and variety, cleanliness of the grain, test weight and operating temperature. These factors will also affect the energy consumption to dry the grain. The drying capacity of a dryer is normally expressed in bushels per hour of wet grain. The deference between wet bushels and dry bushels can be 10% or more depending on the grain moisture content. I will go through the steps of calculating the energy efficiency to demonstrate the calculations. Show it are the data needed to calculate the energy consumption for a drying season. Using an entire drying season reduces the potential for measurement errors. The bushels of corn dried was measured as the grain was delivered to market after drying, so is labeled as dry bushels. The initial moisture content was measured as corn was loaded into the wet holding bin or dryer from the field. The average should be the weighted mathematical average of the moisture contents measured. The final moisture content was calculated from the moisture contents measured as the corn was delivered to market. The fuel use was determined from the fuel delivery slips. Showing on this visual is the procedure for calculating the number of wet bushels if that value is desired. The base moisture content is the final dry moisture content and the actual moisture is the initial wet moisture content in this formula. In this example the 239,592 dry bushels is equivalent to 267,853 wet bushels. The term a bushel can be somewhat confusing since a bushel is defined as both a volume of 1.244 cubic feet and for corn is specified as 56 pounds at 15.5% moisture. The 267,857 wet bushels is confusing since it is the pounds of corn at 23.7 moisture divided by 56 pounds which is the standard bushel weight. The formula for calculating grain moisture shrink cannot be used to determine the pounds of water removed as the grain is dried. To calculate the pounds of water to be removed the weight at both the initial and final moisture content must be calculated based on a 56 pound bushel of corn. Applying the formula to this example with corn at an initial moisture content of 23.69% and a final moisture content of 14.72% yields a wet weight of 62.01 pounds per bushel and a dry weight of 55.49 pounds per bushel. The weight of water removed per bushel then is 6.52 pounds per bushel. As a rule of thumb approximation about 0.7 pounds of water are removed per bushel for each point of moisture corn is dried. Since the weight of water removed is based on a 56 pound bushel if the corn is lighter or heavier the weight of water removed will be affected. The adjustment is proportional to the test weight so multiplying the weight of water removed by the ratio of the test weights provides the adjusted weight of water. For corn with a test weight of 52 pounds per bushel the weight of water removed is 6.05 pounds per bushel rather than 6.52 pounds. Normally the amount of electricity used can be ignored when determining the amount of energy used in high temperature dryers since the amount is usually less than 5% of the energy used. This simplifies the calculations and typically if comparing two high temperature dryers the difference in electrical consumption will be small. The heat content values listed for propane will vary but a common value used for grain drying applications is 91,600 BTUs per gallon. Determining the amount of fuel used can sometimes be a challenge if the amount of fuel remaining in the tank can only be approximated. Use fuel delivery records to be as accurate as possible. Assure that the fuel was used for drying and not for other purposes. The bushels dried used in the energy calculation is the dry bushels because the amount of water removed is based on the standard 56 pound bushel. The gallons of propane used is divided by the number of bushels dried to determine the amount of propane used per bushel. That value is multiplied by the heat content of the propane to provide the energy used per bushel. Finally, that value is divided by the pounds of water removed per bushel to provide the energy consumption per pound of water removed. In this example, 2692 BTUs are required to remove a pound of water. Frequently, a dryer is used to dry more than one type of grain. The process of determining the energy efficiency is the same but the amount of water removed must be calculated for each type of grain and combined to determine the total pounds of water removed. In this example, the dryer was used primarily for corn but some soybeans were also dried. Note that the corn had a very low test weight so the amount of water removed will need to be adjusted for the low test weight. The amount of water removed per bushel of 56 pound corn is calculated to be 7.09 pounds per bushel. Since the corn has a test weight of 48 pounds, the amount of water is adjusted for test weight to be 6.08 pounds per bushel. The water removed from the soybeans is calculated to be 4.45 pounds per bushel. The total weight of water removed is the value calculated for corn added to the weight calculated for soybeans. The energy consumption is then calculated in the same manner as was done previously for one type of grain. The gallons of propane is divided by the pounds of water and multiplied by the heat content of the propane. The energy consumption in this example is 2,295 BTUs per pound of water removed. If a comparison is to be made between the existing dryer and a different dryer, it is necessary to gather information on the proposed dryer. Again, that information may be gathered from company literature which may be on the internet or available from a company representative. Frequently the company literature lists the physical specifications of the dryer and estimated drying capacity but generally will not include the energy efficiency of the dryer. This may be due to the many factors that affect the energy consumption including the factors that affect the drying capacity such as kernel size, chemical composition, variety, maturity, excessive fines, and weather conditions. In addition to dryer design and the factors listed, how the dryer is operated greatly influences energy efficiency. Therefore the drying efficiency value will vary from year to year and between locations. Most of the dryer companies can provide a computer simulation or estimated energy consumption for their dryers. This example is for a CMS 1000H model farm fans dryer used as a full heat dryer where the corn is discharged at 17% moisture. The final moisture removal will occur in a bin as part of the cooling. The input information for this simulation is an outdoor air temperature of 40 degrees and 65% relative humidity. The default values based on the standard for determining drying capacity will be 50 degrees and 50% relative humidity. You need to specify what values you want to be used based on typical outdoor conditions when the dryer will be used. This dryer has four plenum temperatures for the four sections of the dryer. The simulation is run with plenum temperatures of 230, 220, 200, and 170 degrees. The calculated capacity is 1,521 bushels per hour. It is not specified, but since the standard is for drying capacity to be expressed in wet bushels, this is likely wet bushels. The energy efficiency is estimated to be 1,964 BTUs per pound of water removed. The simulation also calculates the fuel used to be 190 gallons of propane per hour and lists the total airflow as 83,440 CFM. This example is a simulation for a TM-1015 model GSI grain dryer. This dryer lists the initial moisture content at 25% and the final moisture at 15%. The amount of energy required increases as the grain dries, so it is important to note the moisture contents used in the simulation. This example is simulated at the default values of 50 degrees and 50% relative humidity. The plenum temperature used is 240 degrees. The listed capacity is 1,202 bushels per hour and the efficiency is 1,497 BTUs per pound of water removed. This energy efficiency would be different at a colder air temperature and higher relative humidity. The grain discharge temperature is listed as 71 degrees. This dryer used suction cooling to capture heat energy from the corn and used it to preheat the air going into the burner and drying portion of the dryer. The dryer also operates at a higher plenum temperature, which improves the energy efficiency. Is the estimated value realistic? It is likely not realistic to expect the energy consumption to be less than about 1,800 BTUs per pound of water removed, even if the dryer incorporated energy efficiency features. There may be times when the value is less with warm outdoor conditions, for example, or for short periods. But generally the energy consumption will likely not be less than about 1,800 BTUs per pound of water removed. Examine the outdoor air temperature and relative humidity used in the simulation to determine if it is representative of the conditions that are typical during drying. Does the predicted energy consumption correspond to the incorporated energy efficiency dryer features or lack of them and the expected energy efficiency of the type of dryer, airflow rate, and drying plenum temperature? Not all dryer companies provide an expected energy efficiency. An estimate can be calculated if some information about the dryer is known. The calculations shown are for the farm fans dryer described before. The brochure states that the airflow is 83,440 CFM and the drying chamber holding capacity is 965 bushels. This is an airflow rate of 86 CFM per bushel, which is typical of farm fans dryers. If the airflow is not provided, tables such as the one in NDSU publication AE 701 grain drying provides the expected static pressure. The airflow can be obtained by knowing the fan specifications and obtaining the airflow from a fan chart provided by the company. Airflow delivered by a fan is affected by blade pitch and other features, so it is best to know the airflow delivery of the fan rather than try to approximate it based on the fan diameter and horsepower, for example. The heat requirement is estimated using the formula shown on the slide. The estimated heat requirement to heat the airflow is 16.5 million BTUs per hour. This calculates to a fuel usage of 180 gallons of LP or propane per hour, which is about 5% less than the company indicates. This value can be used to estimate the energy efficiency of the dryer if the company does not provide an estimate and provides a check on the value calculated by the company. The existing dryer has an energy consumption of 2,692 BTUs per pound and the farm fan's dryer has an energy consumption of 1,964 BTUs per pound. This is a 27% energy savings. For drying 300,000 bushels of corn, this will be a savings of 17,691 gallons of propane, which is a $30,959 savings, assuming a propane price of $1.75 per gallon. The simple payback period is the cost divided by the energy savings. In this example, the payback period is 3.9 years. Any additional costs such as wet holding bins or drain conveyors must be included in the calculation. Natural air or low temperature drying is normally a very efficient method of drying, but this example shows that is true only if the system is sized and operated appropriately. This table shows the bin diameter, corn height or depth, the capacity when filled level full, the horsepower and type of fan on the bin, the airflow rate and if there was a heater on the fan. The minimum desired airflow rate for drying corn at moisture contents up to 21% is 1 CFM per bushel. Two of the bins do not have the desired airflow for natural air drying. The system data is shown on this slide. The average initial and final moisture content of corn is 23.4% and 14% respectively. The amount of corn dried is 64,406 bushels. The average initial and final moisture content of the soybeans is 15.4% and 13% respectively. The amount of soybeans dried is 12,741 bushels. The energy consumption is very high. It exceeds that of a high temperature column dryer even though natural air and low temperature drying is expected to be energy efficient. The system was operated during cold temperatures when the moisture holding capacity of the air is small. Adding the supplemental heat permitted drying but increase the cost. Natural air and low temperature drying is normally inefficient at temperatures near or below freezing. A grain drying energy audit report will normally include the items listed on the slide. Existing system, existing energy use, proposed system, expected energy use, energy savings, simple payback and conclusions. Assure that the person conducting the audit is familiar with grain drying in addition to being competent in conducting an energy audit. More information is available on the web. My website can be found by doing an internet search for NDSU grain drying and storage.