One of the great pleasures of teaching is meeting so many really good people. I enjoy getting to know more about my students than just what their test scores tell me. With so many students starting a second career, we always have a variety of very talented people from all walks of life. One student used to work making custom $5,000 guitars by hand. Others worked as technicians in the telecom industry, and still others in fields such as computer networking. Among this collection of very interesting people, some individuals really stand out for their attitude and leadership. Kelvin Melton always has a smile, an insatiable thirst for knowledge, and a great overall attitude. He is a leader – taking time to help other students. But most of all, he is a consummate professional who truly loves the field of HVACR. Kelvin served his country well – doing two tours as an Army Ranger in Afghanistan. Nobody can outwork Kelvin. He comes to school in the morning after working all night and still is charged up about his studies and sits right up front in the class room. Although I am sure he has had his share of hardships, he never complains, but works diligently towards accomplishing his dream. It has truly been a pleasure to work with him these last two semesters. His enthusiasm inspires other students to up their game. Kelvin died unexpectedly at home two days ago at the age of 26, cutting his promising HVACR career short. I must admit that I am still trying to make sense of it myself. One thing I can truly say is that Kelvin was not waiting for someone else to fulfill his dreams – he was actively pursuing them with every fiber of his being. If you have something that you want to accomplish or a dream to work towards, don’t wait – start working today towards the fulfillment of your goals and dreams. When you get there you can thank Kelvin for showing you how its done.
Friday, February 24, 2012
Saturday, February 18, 2012
Heat Pump Temperature Rise
One of the best ways to check the refrigerant charge of a heat pump during the heating season is to measure the temperature rise across the indoor coil and compare it to data published for that unit. The two main issues with this charging method are getting the required data and measuring the system airflow. Not all manufacturers publish the temperature rise for their equipment. Another potential problem is system airflow. The amount of temperature rise achieved is directly related to the amount of air moving across the coil. If the ACTUAL airflow is different from the manufacturer's stated conditions, the temperature rise will also vary. Increased airflow will reduce the temperature rise and decreased airflow will increase the temperature rise. For the temperature rise method to work, the system must be operating with the correct airflow.
Heat pumps are rated by AHRI for heat output at two outdoor temperatures, 47°F and 17°F. The indoor return air temperature rating point is 70°F. Most heat pumps produce a heat output of close to their "tonnage rating" at the 47°F AHRI rating point and approximately half of their "tonnage rating" at 17°F. Most units operate correctly with an airflow somewhere in the range of 400 CFM per ton of capacity. Of course these are generalizations.
However, a general idea of temperature rise parameters can prove useful. Using these generalized assumptions, let's develop some generalized temperature rise performance parameters. The basic formula to use is BTU = 1.08 x CFM x TEMP RISE. This can be rewritten as TEMP RISE = BTU / (1.08 x CFM). At 47°F the capacity per ton will be 12,000 BTU. Plugging this into the formula we get TEMP RISE = 12,000 / (1.08 x 400). This yields a projected temperature rise of 28°F at a 47°F ambient. On the other end of things, the assumed capacity per ton at 17°F ambient temperature is 6000 BTU. Plugging this in we get TEMP RISE = 6000 / (1.08 x 400). This yields a projected temperature rise of 14°F. You can readily see that the result of a 50% reduction in capacity yields a 50% reduction in temperature rise. Now let's test our mathematical extrapolations against some REAL data taken from a manufacturer’s performance specifications.
Heat pumps are rated by AHRI for heat output at two outdoor temperatures, 47°F and 17°F. The indoor return air temperature rating point is 70°F. Most heat pumps produce a heat output of close to their "tonnage rating" at the 47°F AHRI rating point and approximately half of their "tonnage rating" at 17°F. Most units operate correctly with an airflow somewhere in the range of 400 CFM per ton of capacity. Of course these are generalizations.
However, a general idea of temperature rise parameters can prove useful. Using these generalized assumptions, let's develop some generalized temperature rise performance parameters. The basic formula to use is BTU = 1.08 x CFM x TEMP RISE. This can be rewritten as TEMP RISE = BTU / (1.08 x CFM). At 47°F the capacity per ton will be 12,000 BTU. Plugging this into the formula we get TEMP RISE = 12,000 / (1.08 x 400). This yields a projected temperature rise of 28°F at a 47°F ambient. On the other end of things, the assumed capacity per ton at 17°F ambient temperature is 6000 BTU. Plugging this in we get TEMP RISE = 6000 / (1.08 x 400). This yields a projected temperature rise of 14°F. You can readily see that the result of a 50% reduction in capacity yields a 50% reduction in temperature rise. Now let's test our mathematical extrapolations against some REAL data taken from a manufacturer’s performance specifications.
Model
|
ΔT @ 47°F
|
ΔT @ 17°F
|
BTUh @ 47°F
|
BTUh @ 17°F
|
CFM
|
ERHQ18
|
26°F
|
13°F
|
18,500
|
11,000
|
700
|
ERHQ24
|
25°F
|
12°F
|
24,400
|
12,500
|
800
|
ERHQ30
|
27°F
|
16°F
|
32,200
|
18,800
|
1055
|
ERHQ36
|
26°F
|
13°F
|
36,000
|
19,500
|
1310
|
The manufacturer states that a properly operating unit should be + or – 3°F of these typical values. You will note that our extrapolated values are all within the 3°F margin of error.
But what if the temperature is neither 47°F nor 17°F, what temperature rise do you look for then? Another assumption is in order here; we will assume that the capacity reduction due to ambient temperature drop is even. Since the temperature rise changed from 28°F to 14°F over a 30°F ambient change, this would represent approximately a 1°F change in temperature rise for every 2°F change in ambient temperature. In the above table, we see a temperature rise change of 13°F in 3 out of the 4 units listed. This gives similar results. In our assumed system, 28°F rise at 47°F ambient and a 14°F rise at 17°F ambient, a temperature rise of 23°F would be expected at 37°F ambient based on the relationship of 1°F rise per 2°F ambient temperature. Clearly, manufacturer's data for a specific unit is more accurate than extrapolated benchmarks; however, extrapolated temperature rise calculations are considerably more accurate than blocking the outdoor coil and pretending it's summer. Remember: the best method for charging any unit is the method recommended by the people who made it!
But what if the temperature is neither 47°F nor 17°F, what temperature rise do you look for then? Another assumption is in order here; we will assume that the capacity reduction due to ambient temperature drop is even. Since the temperature rise changed from 28°F to 14°F over a 30°F ambient change, this would represent approximately a 1°F change in temperature rise for every 2°F change in ambient temperature. In the above table, we see a temperature rise change of 13°F in 3 out of the 4 units listed. This gives similar results. In our assumed system, 28°F rise at 47°F ambient and a 14°F rise at 17°F ambient, a temperature rise of 23°F would be expected at 37°F ambient based on the relationship of 1°F rise per 2°F ambient temperature. Clearly, manufacturer's data for a specific unit is more accurate than extrapolated benchmarks; however, extrapolated temperature rise calculations are considerably more accurate than blocking the outdoor coil and pretending it's summer. Remember: the best method for charging any unit is the method recommended by the people who made it!
Saturday, February 11, 2012
What is an LMS?
A Learning Management System, or LMS, is a software approach to organizing and administering a course. Typically, learning management systems are used for online classes. An LMS is basically a web site construction kit that is targeted to education. The LMS allows teachers to manage rosters, design the flow of the course, deliver online content, administer assessments, and calculate grades. For most of us, trying to do just one of these on our own without would be a daunting task. The learning management system makes it possible for teachers to design and administer structured and effective online courses that would probably not be possible without the tools provided by a good learning LMS. Of course web content and technology can be used in traditional classrooms as well as online. The learning management system just makes this far easier. This is not to suggest that today you acquire LMS software and next week you are launching your own Cyber University. There is still quite a learning curve. Because these systems typically can do a lot of things, there is a lot to learn. Although there are many similarities in the different systems, each really has it’s own unique interface and set of tools that you must learn. Compared to the work in a traditional lecture course, I would say there is more work on the front end and less on the back end. This is especially true the first time you offer a course using an LMS. However, the beauty of technology is that once you have that course built, saving, maintaining, and reusing it is relatively easy.
There are many choices for LMS software includng the Open Source program Moodle, commercially hosted systems such as BlackBoard, or systems managed by publishers such as MyHVACLab. Moodle is free, but like all open source freeware, there is a cost, it is just not money. There is good documentation on how things work, but you pretty much have to figure it out for yourself because there is no paid support. There is an active community where you can often get questions answered, but there is no “tech support.” If you are a Linux fan and use Open Office for your general day to day office software, you would probably be very comfortable using Moodle.
BlackBoard is probably the largest and most well known commercially hosted LMS. Many publishers provide Blackboard course “cartridges” to accompany their texts. A cartridge is a collection of resource files, such as pictures, presentations, or test banks that can be loaded into Blackboard to make developing a course easier. Typically a school or school system pays Blackboard to host their courses, allowing teachers to develop courses using their system. Blackboard takes care of the hosting and provides technical support. A downside to this type of hosting is that you can lose all your courses if you decide to go with another system. Our Technical College System switched from Blackboard to Angel a few years back, and the change was abrupt and traumatic.
There are many choices for LMS software includng the Open Source program Moodle, commercially hosted systems such as BlackBoard, or systems managed by publishers such as MyHVACLab. Moodle is free, but like all open source freeware, there is a cost, it is just not money. There is good documentation on how things work, but you pretty much have to figure it out for yourself because there is no paid support. There is an active community where you can often get questions answered, but there is no “tech support.” If you are a Linux fan and use Open Office for your general day to day office software, you would probably be very comfortable using Moodle.
BlackBoard is probably the largest and most well known commercially hosted LMS. Many publishers provide Blackboard course “cartridges” to accompany their texts. A cartridge is a collection of resource files, such as pictures, presentations, or test banks that can be loaded into Blackboard to make developing a course easier. Typically a school or school system pays Blackboard to host their courses, allowing teachers to develop courses using their system. Blackboard takes care of the hosting and provides technical support. A downside to this type of hosting is that you can lose all your courses if you decide to go with another system. Our Technical College System switched from Blackboard to Angel a few years back, and the change was abrupt and traumatic.
A third option is an LMS hosted by a publisher such as Pearson. Pearson has been offering online courseware for many years. One of the most well-known is MyMathLab which is used by thousands of schools all over the country. Publisher managed learning management systems are usually designed to support a particular text, so integration with the text is very easy. A big advantage of the publisher systems is that they deliver a finished product, ready to use. Moodle and Blackboard deliver a platform on which to build, but you still need to build the courses. MyHVACLab accompanies Fundamentals of HVACR. It is a complete course including e-book, interactive activities, and assessments all organized around the structure of the book. You can still make the course your own by editing, rearranging, adding, or deleting; but you start out with a complete course right out of the box. Also, you don't have to worry about your school system's contract expiring and losing all your classes. MyHVACLab does not cost the school anything to use. Instead, students pay a modest access fee. When bundled with the book, the cost is usually only $!5 - $20 more than the cost of a book by itself.
This post is a little long, but we have just scratched the surface. There is no question that using an LMS requires a good deal of effort, but I believe if you make the effort you will find it very rewarding.
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