September 22, 2011
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I am back from a bit of a break and have been doing some solar monitoring projects using flow meters. The benefit of the flow meter is it allows you to do an energy calculation and determine just how much energy the solar panels are saving you. Up until now I have been working on measuring the glycol energy, and the glycol uses a constant flow rate. The water side of the system is different because the flow is based on the buildings hot water demand. Without a flow meter or an estimated flow rate all you are really doing is measuring temperatures. Flow meters work by sending an electric pulse every time a specific volume of fluid passes them. Most give one pulse per gallon or one pulse per 10 gallons. The Web Energy Logger (WEL) counts how many of these pulses you receive each minute. You can easily scale this value with the WEL’s programming to whatever engineering units you want. I prefer liters per second. Once you have the WEL measuring the flow properly you can move on to the energy calculations.
The formula for calculating the solar output is as follows:
Solar Heat Output = (volume flow rate)*(density of the fluid)*(specific heat of fluid)*(temperature differential created by the solar system)
You can also calculate the total heating required by the building by measuring the temperature differential between the cold water supply and the final hot water on the outlet of the furnace. You apply the same formula as the solar output but using the new temperature differential.
Total Heating = (volume flow rate)*(density of the fluid)*(specific heat of fluid)*(temperature differential created by the entire heating system)
The total heating value can be used to calculate the percentage of the total water heating load that the solar system is able to meet. This percentage is known as the solar fraction.
Solar Fraction = (solar heat output) / (total heating) * 100
If you are monitoring an active solar system (one that uses electricity to run) then you will need to subtract the electrical energy used by the pump and control system from the solar output to get a fair representation of how much you are indeed saving. In most cases the equipment will use a minimal amount of energy but it is important to factor it in because over the course of the year it does add up.
Once you have the WEL calculating these values you can start logging daily, monthly, and annual totals. This will provide great insight into the effectiveness of your solar thermal system. It is important to note that without measurement you can never be sure that the system is working even if it is brand new. The math formulas and calculations for monitoring solar systems might seem a little tedious at first but before long it will become old hat.
An example of this in action can be found here: http://www.welserver.com/WEL0512/
A flow meter with an electronic pulse head counter
The above flow meter installed on a domestic hot water system
June 25, 2011
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Friday was my final day with NSCC Applied Research working full time. When I left Friday the monitoring system was not live. There are still some challenges to overcome with this very large project. When we replaced the wire with CAT5 network wire the system worked for a little while but then we started getting shorted bus errors. Because of the number of connections the resistance on the wire was too high. We will need to solder the connections instead of using quick connect clips in order to improve the signal. The WEL sends 5V over the 1-wire bus and because of the amount of quick connects we used for sensors runs we were getting too much resistance and noise on the line. We reduced the system to include only one of the evacuated tube collectors and the signal returned to normal. Once the soldering is done we can include the others again.
Our network connection is browning out as well. We are able to get a wireless signal on the roof with the equipment we have but we can’t keep it connected. This meant we couldn’t go live with the system. We will need to replace the antenna with something stronger. We have an access point on the roof for the solar photovoltaic monitoring and we may need to try connecting through that as well. That would require significant changes to the way the photovoltaic monitoring system communicates though so we would consider that a last resort.
I leave the project in the very capable hands of Dr. Alain Joseph and they rest of the crew. They will continue to move the project forward and I expect to see the system live this summer. I prepared a manual for them documenting the process of solar hot water monitoring using the WEL. I’m sure that will provide them with the knowledge transfer required for someone else to step in and continue the project. I have also agreed to offer them support on a part time basis as needed.
The experience of working on a large project like this one has been very valuable to me. We’ve worked through a number of different problems, and learned to anticipate things to go wrong. I know now that I shouldn’t expect anything to work right the first time. I also learned the importance of documenting your work properly, so that others can pick up where you left off.
June 24, 2011
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Getting a pyranometer to work with the Web Energy Logger (WEL) was a long process for us in the lab. A pyranometer is a device that measures the solar intensity in watts per meter squared. We used a 0-5V pyranometer from Apogee (http://www.apogeeinstruments.com/pyranometer/). This was a challenge because the WEL does not have a 0-5V input. We needed to convert the signal to 4-20 mA so that it could be read by the WEL. There is a benefit to 4-20mA though since it is a current signal and not voltage it doesn’t drop off when you use a long wire run. Originally we had an electronics student design us a signal converting circuit board because we had the tools to design and mill circuit boards here at the college. We found a company that manufactures boards like this (http://controlsignalconverter.com/) and it is much more practical to purchase them then make them in most cases.
When testing the pyranometer we noticed that the 4-20 mA signal would drop off around the 12 or 13 mA mark and saturate. The WEL would never receive the full 20 mA. We ran numerous tests with our equipment and determined that the problem was within the WEL itself. We spoke to the manufacturer of the WEL and he explained the problem and how to fix it. It requires some cutting to fix it. There are two zener diodes inside the WEL that need to be snipped off. To do this you need to remove the rabbit board network chip by wiggling it and lifting it at the same time. It is fairly snug so you will need to work at it to get it off. Once it is off you will have access to the zener diodes and you can snip them out with some wire cutters. You will see them next to the green 4-20 mA plug on the WEL sandwiched between two resistors. I took a picture of our board with them removed below and have identified where they used to be with a red circle. Once we removed the zener diodes it worked perfectly.
You need to scale the numbers in order to get the proper engineering units. We used the formula f(x)=78.125x-312.5 to convert the 4-20 mA signal into watts per meter squared. This was specific to the equipment we used so if you use a different pyranometer you will need to do the math yourself.
Pyranometers are important for research because they allow you to see how solar panel output changes with solar intensity. We are particularly interested in how solar performs in the winter time in our climate. It is cold but often the sun is shining. With a pyranometer in our system we will be able to draw more meaningful conclusions from our data.
June 23, 2011
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Today I travelled to Bridgewater, NS to help an industry partner repair a Web Energy Logger (WEL) installation. The solar system uses 30 evacuated tube collectors to supply heat to an in-floor heating loop and dumps the heat in the summer time. Since I did not take part in the original monitoring system installation this presented challenges that were new to me. I had to look over the monitoring system to understand what it was doing before I started work. I needed to not just be able to understand how it was working, but also make sure that it was working. I located the sensors that were installed and tested their readings against readings on my temperature gun. I found one sensor that was not reading properly and replaced it with a new one. I also installed a current sensing switch on the glycol pump to detect when it is running. Since the in-floor heat loop has a constant flow rate we don’t need to install a flow meter to determine the heat provided by the system. I programmed the WEL with some thermodynamics calculations related to mass flow and it now calculates the energy output in kWh.
The repair job took just over an hour and I gained valuable experience in interpreting the work of others. Its easy to jump in and repair a system you set up yourself but when you are trying to follow the work of others it can be a challenge. Pictured below is the box containing the WEL and router (LEFT) and the building with evacuated tube solar collectors on the roof (RIGHT).
June 20, 2011
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The solar thermal monitoring project is moving along despite a couple of setbacks. We received the wireless equipment in the mail and were able to set up the wireless bridge to the schools wireless network. We used a directional antenna to improve the reception because the school’s wireless signal on the roof is weak.
We put a 12V deep cycle battery on the roof and we did a test run. It was able to power both the router and the Web Energy Logger (WEL). The battery is rated at 90 amp hours and the load for both the WEL and router is 0.4 amps combined. This means we are able to get over 3 months of power off the battery before we will need to swap it out for charging. This is good news because the battery is very heavy!
Testing with the pyranometer hit a bit of a wall initially. As I mentioned in my previous post the pyranometer measures the solar intensity in watts per meter squared. Since we are converting the 0-5V signal on the pyranometer to a 4-20 mA (milliamp) signal for the WEL we needed to scale the results. We did the math calculation and did a test run. We weren’t getting to the proper numbers in the upper ranges. Once we were confident the math was correct we tried numerous 4-20 mA devices with the WEL and had the same result. It really pays to have an electrical engineering student around when you are trying to troubleshoot electrical problems. Travis Keeping is our electrical expert at the lab and he a bunch of tests for us. In the end a call to Phil Malone from OurCoolHouse.com who designed the WEL was all it took to discover our problem. Turns out that the WEL has a defect and there are two zener diodes that we will need to snip out of the circuit and it should work fine after that. Phil also told us that new versions of the WEL will have a voltage port so we won’t need to convert the signal in the future. We have another WEL on order and it will have the voltage connection on it.
The wire we chose for the sensor wire run was cheap wire and it started giving us grief. We used a 75m run and it had too much resistance because it wasn’t twisted pair wire. Twisted pair wire helps to reduce the electrical noise on the signal. We started getting “shorted bus” errors on the WEL. I took the wire run down and we will be replacing it with CAT 5 wire, which is what is used for computer network cables. Once the new wire is installed we should be able to go live.
June 6, 2011
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We are working on an electronic monitoring system for the solar thermal gear on the roof of the NSCC Waterfront Campus. The roof has 2 arrays of Thermodynamics flat plate collectors as well as 2 arrays of Thermomax evacuated tube collectors. We will be monitoring the glycol temperatures, outside air temperature, and solar radiation. The data logging will be done using the Web Energy Logger (WEL) over the Wel Server. I have installed the temperature sensors and programmed the logic for the calculations inside the WEL. We are interested in adding flow meters to this project if we can find ones within our price range and get permission from facilities management to install them.
The challenge with working on the roof is that there isn’t power or wired network access. The campus has a very weak wireless signal on the roof and I will be connecting the WEL to the internet that way by using a wireless bridging router. The router runs off 12V and the WEL can also run off of 12V. For now I will power the entire setup off of a large deep cycle battery and it will need to be changed and charged from time to time. NSCC Applied Research may add a photovoltaic panel to the roof to power the equipment and charge the battery at a later time.
This project is unique from the residential and commercial installs I have done in the past because it will be used primarily for research. An electronics student at the college was able to design us a voltage to milliamp converting circuit board that will allow us to connect a pyranometer with a voltage output to the 4-20 mA input on the WEL. By using a pyranometer and air temperature sensor I will be able to match the energy output to the solar radiation and determine the energy efficiency of the gear. I will also be able to do statistical analysis over time. The lab will be very interested in the variance of the different readings and how they relate to each other. By comparing sunny days in the winter to days with the same amount of solar radiation in the summer we will be able to determine the effect of outside air temperature on the output of the different types of collectors. This is of particular interest because our winters are cold but the sun is usually shining.
I will be posting more information as this project progresses.
The Thermomax evacuated tube collectors are the dark blue tubes on the left of the roof. The Thermodynamics flat plat collectors are the small grey rectangular panels with the black border.
May 31, 2011
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Today I installed a web energy logger on a solar thermal system in Halifax. The system is in a large multi-floor residential building. The entire process took about 3 hours, which is a new record for me. The solar data logging system installed has 5 temperature sensors and a current switch to detect if the pump is on. With this setup we are able to calculate the amount of energy that the solar panels are able to extract from the sun and supply to the glycol. The data logger will provide real time data once each minute as well as log the data to a .csv file for analysis at a later time. It connects to the WEL Server (www.welserver.com) to transmit the data over the internet.
The limitation of this data logging system configuration is that it is unable to calculate how much of that energy is actually transferred to the water. Since the solar system was already installed prior to the decision to add a data logger, it does not have electronic pulse flow meters. Flow meters connected to the data logger would allow for accurate calculations of the energy supplied to residents and the savings on the buildings power bill associated with that energy. The decision to go back and install pulse flow meters will rest with the building owner.
May 10, 2011
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The WEL is a low cost but effective data logger that can be used to monitor energy use or generation. It contains a one wire bus that allows digital sensors to be strung along like christmas tree lights. It also contains 6 pulse inputs, 8 run inputs, and 2 4-20 mA analog inputs. Pulse sensors return an electronic pulse signal and applications may include paddlewheel flow meters for water flow. The digital pulses can be counted and converted into a volume flow rate. Run sensors tell you if the device connected is on or not. Current switches can be installed over power cables to current and return an on/off signal. 4-20 mA sensors send a mA current signal that can be scaled into engineering units.
Inside the WEL you are allowed 150 variables. These can be sensor inputs, constants, or simple expressions of other variables. The WEL has limited internal memory so it is limited to simple 2 variable expressions and is not capable of doing exponents or square roots. That being said most energy calculations can still be performed inside the WEL. It also has support built in to maintain running totals for the day, month, or year of any variable.
The WEL uses a rabbit board network chip to connect to the internet and transmit the data. It can be set to log data at any frequency, entered in minutes. By default it connects to the WELserver (http://www.welserver.com). This webpage contains a map of the world with all the other WEL’s shown on it. It is a great tool because it allows you to not only monitor your system, but see how others are doing as well. With some ingenuity you can connect the WEL to your own server to record and present the data there. The WEL posts data that can be received by a simple CGI or PHP script.
Typical WEL applications include monitoring of geothermal, solar thermal, solar photovoltaic, and energy use. The WEL is diverse enough to be used in other applications as well. A device called the WattNode (http://www.ccontrolsys.com/w/Advanced_Pulse_WattNode) must be added if you want to measure alternating current.