A Design Analysis of Solar Thermal Systems for Cardinal Newman Hall

By: Randall Lessard

Spring 2014ET 494-01

Instructor: Dr. Cris KoutsegourasAdvisors: Dr. Rana Mitra

Mr. Byron Patterson

Abstract:

Cardinal Newman Hall, on Southeastern’s campus, is a residential building for students and an office building for some professors. This building is the upcoming site for one of the

Sustainability Center’s solar thermal projects. For this project, I will be advised by Dr. Rana Mitra and the Director of the Physical Plant, Mr. Byron Patterson. The initial idea of this project

was to design and install two independent solar thermal systems that would be integrated into already existing water heating systems for the building, providing heated water to the boilers and building via solar energy. However, due to circumstances beyond my control, the installation has

been prolonged. The current objective is to complete the design process for the solar thermal systems. The results will be used to provide a design analysis and a study on thermal

performance with varying weather conditions. The applications of solar thermal systems for Cardinal Newman Hall are anticipated to deliver a beneficial, cost-effective energy solution for

Southeastern in the future.

Solar Thermal System / Process:

Generally speaking, a solar thermal system consists of these main components:

Solar thermal collectors Tubing Heat-transport fluid Pumping station Heat exchanger Controller Expansion tank Various valves

The process begins by absorbing solar radiation through a solar thermal collector. A collector is a device consisting of a highly-selective absorber plate attached to a meandered copper tubing underlay. The face of a collector is covered in a transparent, solar safety glass to maximize light absorption.

Within the copper piping flows a heat-transport fluid. This fluid is preferably propylene glycol because of its high thermal conductivity and non-toxic emission properties. The fluid is pumped through an array of collectors via the supply line at a slow speed absorbing thermal energy created by the collectors. At the end of an array, there is a pressure relief valve and also an air vent attached to the outer tubing to maintain a safe pressure. Ball valves are also placed along the outer tubing to control the flow of the heat-transport

Figure 2 (Commercial Solar Flat Plate Collectors)

Figure 3 (Pumping Station

fluid. The heat-transport fluid then flows through the return line to a pumping station. A pumping station consists of a pump, a controller, safety valves, and a connection for an expansion tank.

The controller is an electronic device that provides a digital monitoring display. It can measure many parameters of the solar thermal system and is used to adjust settings for the solar system such as flow rate and desired heat. Some typical data that can be measured by the controller is the temperature of the heat-transport fluid and water in the system, amount of solar energy being absorbed by the collectors, and warnings if there are errors in the system. An expansion tank is a sort of safety measure that is used to protect the system from excessive pressure that builds during thermal expansion of water.

From the pumping station, return and supply lines pass through a heat exchanger. A heat exchanger consists of a collection of slightly separated metal plates pressed together to pass heat from one medium to another. These exchangers are made of a highly thermal conductive metal such as copper which has a thermal conductivity of 231 Btu/(hr-ft-F). The return line (filled with propylene glycol) from the collectors and the supply line to a boiler (filled with water) wind through the heat exchanger. The heat from the return line is transferred to the supply line, heating the water.

The heated water is then pumped to a boiler or water tank by a circulating pump. However, before flowing into the boiler, the heated water will pass a sensor that determines if it is needed in the boiler to maintain the desired temperature within. If so, the heated water will flow into the boiler. Once the desired temperature in the boiler is reached from the added hot water, it will shut off. If not, it will bypass the boiler and return to circulation. This process effectively reduces the operation time and energy consumption of the boiler.

Project Description:

The solar thermal systems in this project will utilize solar energy to generate thermal energy to ultimately assist in the heating of water for both the domestic hot water and heating water systems of Cardinal Newman Hall. The existing water systems are located a short distance

Figure 4 (Solar Brazed Plate Heat Exchanger)

away in the boiler room due southwest of Cardinal Newman Hall. By using a renewable resource to heat water for the building, this project will cut energy costs down and be an effective eco-friendly energy solution. Currently, the installation has been prolonged and will not be completed this semester.

The project objectives have been altered by this and now consist of these main steps:

A. Design the size of the systems to match the boiler heating water system and the domestic hot water system.

B. Determine size of all pumps and heat exchangers to match head pressure and maximize efficiency.

C. Design and determine the most efficient placement of the solar thermal system components.

D. Analyze changes in performance of solar thermal systems for varying weather scenarios.

Study:

During the first month of the project I met with Mr. Byron Patterson, Director of the Physical Plant, to get an actual look at how solar thermal systems work. I was shown the solar thermal applications on campus at the Kinesiology building and Biology building to become familiar with solar thermal systems. I was also introduced to the boiler room for Cardinal Newman Hall at this time. Mr. Patterson explained to me how the heating water systems and domestic water systems work for the building.

It was at this time that I decided it would be most efficient to install the solar collectors on top of the boiler room. This will decrease the amount of piping needed which in turn decreases heat loss throughout the system. There are two I-beam supports spanning across the top of the boiler room that would be ideal to support the installation of solar collectors. The collectors will face the true south direction with at least an angle of 15° and no more than 70° for

best performance. In addition, spots were chosen in the boiler room to place the pumping stations for the solar thermal systems.

.

As for solar collectors, I have conducted research on Schuco collectors and Lochinvar collectors due to their overall performance. They both offer very efficient collectors that would be suitable for this project. Specifically, the Schuco CTE 520 CH would be a great collector choice. They have a rated thermal output of 2.0 kW, and use a unique thermal conduction technology. The absorber has a surface area of 27.13 ft² and a heat transfer fluid capacity of 0.46 gallons. (Schuco Collector) Lochinvar’s SLV solar collector is another viable option. The SLV collectors have a performance rating of 28,400 BTU/day, but have a slightly smaller absorber. However, they are able to carry 0.55 gallons of heat transfer fluid.(SLV/SVH Collectors) Both collectors are about the same size and would be able to stand in arrays of 4 on the roof of the boiler room.

It was later concluded that Lochinvar SCH090 collectors would be the best option. The SCHO090 collector is actually an array of 4 collectors that is 6’7” x 13’2”. This collector has a thermal performance rating of 84,500 Btu/day with an absorber surface area of 79.76 ft². It is capable of holding 1.9 gallons of heat-transfer fluid and has a recommended flow rate of .872 gpm. Additionally, the Lochinvar system installed on the Kinesiology building on campus proves to be more efficient for a solar thermal application compared to the Schuco collector system installed on the Biology building. (Lochinvar/TiSUN)

In later meetings, I was taken back to Cardinal Newman Hall to take measurements of the existing water systems, components, and the size of the building. I will use this information to calculate flow rates for the inlets and outlets of the pumps for each system.

Measurements:

PUMPS Heating Water Pump Domestic Hot Water Pump (Taco 2400-45)

Inlet Pipe Size (in) 1 ¾ 2Outlet Pipe Size (in) 1 1 ½

BOILERS Boiler (Thermo Pak GW-1050)

Domestic Boiler (Copperglas 40-CGA)

Input (btu/hr) 1,050,000 400,000Working Pressure (psi) 75 125

Capacity (gal) 120 250Fuel Natural Gas Natural Gas

BOILER ROOM SIZE (ft)(L x W x H) 19 x 17 x 12

To connect the solar thermal systems to the existing water systems copper tubing will be used. Copper is the most logical material to be used in solar thermal systems because it is has the best thermal conductivity of all engineering metals, it is highly resistant to both atmospheric and aqueous corrosion, and it is easy to fabricate and to join by soldering or brazing. The thermal advantages of copper means thinner tubing can be used to absorb the same amount or more heat than aluminum or steel tubes of larger sizes. Copper is also more cost-effective and reliable in this application. Specifically, type L copper tubing is preferred in hot water systems and solar applications. (Copper Development Association Inc.)

Methodology:

Since the project has become an analysis rather than a build, an array of reasonable specifications or conditions was created for most calculations in this project to compare and contrast different outcomes to determine the most efficient combinations.

I. Calculate flow rates and head loss of existing systems.

My first objective was to calculate the amount of water being pumped through the existing water systems. After talking with Dr. Mitra and going over possible ways to find a solution, I referred to the textbook Applied Fluid Mechanics: Sixth Edition to obtain the needed equations. First, the volume flow rate equation is:

Q=Av (1)

Where Q is the volume flow rate (ft³/s), A is the cross sectional area of a pipe (in²), and v is the velocity of the fluid flow (ft/s). (Mott, 2000)

Upon finding the flow rates I will be able to determine head pressure drop in each system by using the Darcy–Weisbach equation:

h f=f D∙ LD

∙ V 2

2 g(2)

Where h f is the head loss due to friction (ft), f D is the Darcy friction factor, L is the length of the pipe (ft), D is the internal diameter of a pipe (in), V is the velocity of the fluid flow (ft/s), and g is the acceleration due to gravity (ft/s²). (Mott, 2000)

Using copper tube data provided by The Copper Tube Handbook, I calculated flow rates and head loss for each existing system using possible fluid velocities to determine the most efficient pumping station to be integrated into both systems. (Appendix A)

II. Selection of pumping stations and heat exchangers.

The next step was to find suitable pumping stations for the collector arrays. Being that Lochinvar collectors were chosen for their efficiency and size, I leaned more towards a Lochinvar pumping station to begin with. After comparing 5 commercial pumping stations suitable for these applications, I chose the Lochinvar SPS0250 pumping station. It includes a Grundfos UPS 25-58U circulating pump that is capable of handling flow rates of .26-3.17gpm and is rated to handle up to 250 ft2

of collector area. The station includes a LCD solar control unit with an integrated energy balance function, as well as a flow sensor, pressure gauge, and thermometer. (Solar Pump Station )

As for heat exchangers, I stayed with Lochinvar, specifically the HEX20025 Solar Brazed Plate Heat Exchanger. The plates are made of 316L Stainless Steel and brazed with copper. This model can handle up to 450psi at 350°F. (Heat Exchanger)

To determine how effective the heat exchanger is, a working model will be created in COMSOL. It will demonstrate how much heat can be transferred from the solar array line to the existing system water line.

III. Placement of components.

The most efficient locations to install the collector arrays and pumping stations for each system have already been established. The collector arrays should be installed into the I-beam supports on the roof, facing true south at a 30° angle for maximum efficiency. The spots chosen for the pumping stations will provide an easy route for supply lines to go directly up through the roof and to the arrays. This will also ensure an accurate reading of the fluid temperature at the inlet of the arrays and allow the user to fine tune the flow rate of fluid right before passing through the arrays.

Figure 6 Lochinvar SPS0250

Figure 7 Heat Exchanger Model

The heat exchangers, however, will be placed on the wall, along the return lines at half the distance from the array lines to the existing system supply lines to reach a conservative median between the two systems and still offer efficient heat transfer.

IV. Calculate thermal efficiency of collectors.

Once all components were selected, I then analyzed the thermal performance of the collectors and, ultimately, the efficiency of the system. To do this, a set of heat flow equations are needed as well as certain specifications of the Lochinvar SCH090 collectors which are found on the SRCC OG-100 certification and rating sheet.(Certified Solar Collector)

To measure thermal performance, it is necessary to define step-by-step heat flow equations to find the final equations of the collector system. This method of calculating thermal efficiency of collectors is credited to Fabio Struckmann of the Department of Energy Sciences at Lund University, Sweden. See Appendix B for nomenclature.(Struckmann, 2008)

The amount of solar radiation received by the collector is:

Qi=IA (3)

However, a part of this radiation is reflected back to the sky. Basically, the conversion factor indicates the percentage of the solar rays penetrating the cover of the collector and the percentage of radiation being absorbed. Therefore, it is the product of the rate of transmission of the collector cover and the absorption rate of the absorber, expressed as:

Qi=I (τα ) A(4)

As the collector absorbs heat, the surface becomes higher than the surrounding and some thermal energy is transmitted back to the atmosphere. The rate of heat loss is expressed as:

Qo=U L A (T c−Ta)(5)

Thus, the rate of useful energy extracted by the collector is expressed as a rate of extraction under steady state conditions, proportional to the rate of useful energy absorbed by the collector, minus the amount lost to the surrounding atmosphere. This is expressed as:

Qu=Qi−Qo=IταA−UL A (T c−Ta)(6)

However, this equation proves to be somewhat inappropriate because of the difficulty to define an average collector temperature. A more definite collector heat removal factor can be defined as:

FR=m Cp(T o−T i)

A [I τα−UL (T i−T a )](7)

When the whole collector is at the inlet fluid temperature, the maximum possible useful energy gain in a solar collector is achieved. According to the Hottel-Whillier-Blisseuation equation, the actual useful energy gain is:

Qu=A c ∆t F R[I T ( τα )n−U L (T i−T a )](8)

The measure of a flat plate collector performance is defined as the ratio of useful energy gain to the incident solar energy over a period of time:

η=∫Qu dt

A∫ Idt(9)

So the instantaneous thermal efficiency of the collector is:

η=FR τα−F RU L (T i−T a

I )(10)

Assuming thatFR,τ , α ,U L are constants for a given collector and flow rate, then the collector efficiency is a linear function of the three parameters, Solar irradiance (I), fluid inlet temperature (T i), and ambient air temperature (T a). These three parameters can be approximated using experimental data. By plotting the collector efficiency, η , against (T i−T a)/I , this will give a single line where the slope represents the rate of heat loss, −FR U L, from the collector. (Struckmann, 2008)

Analysis/Results:

Referring to the technical information on the specification sheet for the collectors, the efficiency equation obtained by SRCC concludes a y-intercept (FR τα ¿ of 0.714 and a slope (−FR U L) of -0.698 Btu/hr.ft2.°F. Using these values of maximum efficiency and a set of 3 likely transmission coefficient of glazing () and absorption coefficient of plate () values determined by the recommended flow rate of solar fluid through the collectors, 3 possible collector heat removal factors (FR) and collector overall heat loss coefficients (U L) were calculated.

To obtain collector efficiency, the minimum, average, and maximum intensity of solar radiation during the months of July (summer) and January (winter) for the latitude of 30° N (Hammond, LA) was researched through various resources. (U.S. Solar Radiation Resource

Maps)This was taken a step further by including the intensity of solar radiation for clear, mildly cloudy, and cloudy weather conditions for each month as provided by the SRCC. (Certified Solar Collector)

Since collectors for water heating systems are designed to operate through the colder winter months and at higher temperatures in the wide range of 25 – 125 °F above ambient, depending on season and location, the experimental temperature gradient (T i−T a) used ranges from 30°F - 120°F.

The experimental data was then input into the efficiency equation and represented by a line curve to demonstrate the efficiency of the Lochinvar SCH090 collectors given certain parameters. An example of collector efficiency for the month of July using minimum, average, and maximum intensity of solar radiation received as well as clear, mildly cloudy, and cloudy conditions is shown below using the 1st set of calculated parameters:

FR τ α U L I(min) I(avg) I(max) I(clear) I(mild) I(cloudy)

1.36

0.70 0.75 0.513 Btu/hr.ft2.°F

1267 Btu/hr.ft2.°F

1426 Btu/hr.ft2.°F

1584 Btu/hr.ft2.°F

1115 Btu/hr.ft2.°F

769 Btu/hr.ft2.°F

426 Btu/hr.ft2.°F

SUMMERmin avg max0.697 0.699 0.7010.692 0.694 0.6960.686 0.690 0.6920.681 0.685 0.6880.675 0.680 0.6830.670 0.675 0.6790.664 0.670 0.6740.659 0.665 0.6700.653 0.660 0.6660.648 0.655 0.661

SUMMERclear mild cloudy0.695 0.687 0.6650.689 0.678 0.6480.683 0.669 0.6320.676 0.660 0.6160.670 0.650 0.5990.664 0.641 0.5830.658 0.632 0.5670.651 0.623 0.5500.645 0.614 0.5340.639 0.605 0.517

(Ti-Ta)30405060708090

100110120

These graphs show how the efficiency of collectors drops significantly during cloudy conditions, especially in colder weather when the temperature gradient is larger. It can also be determined that the rate at which efficiency drops is linear. According to the line graphs, the efficiency of these collectors during winter months is only slightly lower than during summer months. The difference is only great during winter months with cloudy conditions, the thermal efficiency drops rapidly with an increased temperature gradient. All parameters,experimental data, and graphs are included in Appendix B-E.

The objective of this project was to determine 2 efficient solar thermal system to provide heat to the supply lines of the existing boiler systems. If one were to install the aforementioned components described in this report, the collectors would prove to be 67.7% efficient during warmer months and 66.2% efficient during colder months.

Previous Issues:

Due to the lack of financial support this semester, the original concept of the project was cut short. With this setback, the deliverables were changed accordingly to suit the current situation.

References:

Mott, R. L. (2000). Applied Fluid Mechanics (6th ed.). Upper Saddle River, N.J.: Prentice Hall.

30 40 50 60 70 80 90 100 110 1200.6200.6300.6400.6500.6600.6700.6800.6900.7000.710

Summer

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Efficie

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(%)

30 40 50 60 70 80 90 100 110 1200.400

0.450

0.500

0.550

0.600

0.650

0.700

0.750

Summer

clearmildcloudy

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(%)

Schuco Collector CTE 520 CH and CTE 520 CH1. (n.d.). Schuco. Retrieved December 2, 2013, from http://www.schueco.com/web/uk/partner/solarstrom_und_waerme/products/solar_thermal_transfer/solar_thermal_collectors/schueco_kollektor_cte_520_ch_und_cte_520_ch_1_der_premium-linie

Installation & Operation Manual: SLV/SVH Collectors. (n.d.). Lochinvar Commercial Solar Systems. Retrieved December 2, 2013, from http://www.lochinvar.com/_linefiles/SL-I-O Rev B.pdf

Lochinvar/TiSUN. (n.d.). Typical Specification: SCH-SPEC-01. Retrieved February 25, 2014.

Copper Development Association Inc. (2010). The Copper Tube Handbook. New York, NY: Copper Development Association Inc. Retrieved March 7, 2014, from http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf

Solar Hot Water & Heating Manufacturer. (n.d.). Design Resources: Choosing the Right System Type. Retrieved March 7, 2014, from http://www.sunmaxxsolar.com/choosing-the-system-type.php

Solar Brazed Plate Heat Exchanger. (n.d.). Lochinvar Products. Retrieved March 7, 2014, from http://www.lochinvar.com/products/default.aspx?type=productline&lineid=176

Commercial Solar Flat Plate Collectors. (n.d.). Lochinvar Products. Retrieved March 7, 2014, from http://www.lochinvar.com/products/Default.aspx?lineid=153&type=productline

Certified Solar Collector. (September 2010). Lochinvar/TiSun Glazed Flat-Plate. Retrieved April 20, 2014, from http://www.lochinvar.com/_linefiles/SCH090.pdf

Solar Brazed Plate Heat Exchanger. (n.d.). Lochinvar/TiSun Commercial Solar Thermal Systems. Retrieved April 21, 2014, from http://www.lochinvar.com/_linefiles/SBP-02.pdf

U.S. Solar Radiation Resource Maps. (n.d.). U.S. Solar Radiation Resource Maps. Retrieved April 22, 2014, from http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/

Installation & Operation Manual: Solar Pump Station. (n.d.). Lochinvar Commercial Solar Systems. Retrieved December 2, 2013, from http://www.lochinvar.com/_linefiles/SL-PS-I-O-Rev%20B.pdf

Struckmann, Fabio. (2008). Analysis of a Flat-Plate Solar Collector. Retrieved April 22, 2014. From http://www.ht.energy.lth.se/fileadmin/ht/Kurser/MVK160/Project_08/Fabio.pdf

Appendix A

Qi – collector heat input, Btu/hr

Qo – heat loss, Btu/hr

Qu – useful energy gain, Btu/hr

I – intensity of solar radiation, Btu/hr.ft2.°F

A – collector area, ft2

FR– collector heat removal factor

Tc – collector average temperature, °F

Ti – inlet fluid temperature, °F

Ta – ambient temperature, °F

U L– collector overall heat loss coefficient, Btu/hr.ft2.°F

m – mass flow rate of fluid through the collector, lb/s

- transmission coefficient of glazing

- absorption coefficient of plate

η – collector efficiency

Appendix B

Collector heat removal factor (FR) Transmission coeffi cient of glazing (tau) tau alpha Absorption coeffi cient of plate (alpha) Collector overall heat loss coefficient (UsubL)1.36 0.700 0.525 0.75 0.5131.09 0.8 0.656 0.82 0.640.88 0.9 0.81 0.9 0.79

min avg maxSummer(July) 1267 1426 1584Winter (Jan) 792 1014 1584

clear mild cloudySummer(July) 1115 769 426Winter (Jan) 718 406 113.5

(Ti-Ta)30405060708090

100110120

Appendix C

SUMMER WINTER SUMMER WINTERmin avg max min avg max clear mild cloudy clear mild cloudy0.697 0.699 0.701 0.688 0.693 0.701 0.695 0.687 0.665 0.685 0.662 0.5300.692 0.694 0.696 0.679 0.686 0.696 0.689 0.678 0.648 0.675 0.645 0.4680.686 0.690 0.692 0.670 0.680 0.692 0.683 0.669 0.632 0.665 0.628 0.4070.681 0.685 0.688 0.661 0.673 0.688 0.676 0.660 0.616 0.656 0.611 0.3450.675 0.680 0.683 0.652 0.666 0.683 0.670 0.650 0.599 0.646 0.594 0.2840.670 0.675 0.679 0.644 0.659 0.679 0.664 0.641 0.583 0.636 0.577 0.2220.664 0.670 0.674 0.635 0.652 0.674 0.658 0.632 0.567 0.627 0.559 0.1610.659 0.665 0.670 0.626 0.645 0.670 0.651 0.623 0.550 0.617 0.542 0.0990.653 0.660 0.666 0.617 0.638 0.666 0.645 0.614 0.534 0.607 0.525 0.0380.648 0.655 0.661 0.608 0.631 0.661 0.639 0.605 0.517 0.597 0.508 -0.024

1st tier conditions

Appendix D

SUMMER WINTER SUMMER WINTERmin avg max min avg max clear mild cloudy clear mild cloudy0.699 0.700 0.702 0.689 0.694 0.702 0.696 0.688 0.666 0.686 0.663 0.5310.693 0.695 0.697 0.680 0.688 0.697 0.690 0.679 0.650 0.676 0.646 0.4690.688 0.691 0.693 0.671 0.681 0.693 0.684 0.670 0.633 0.666 0.629 0.4080.682 0.686 0.689 0.662 0.674 0.689 0.678 0.661 0.617 0.657 0.612 0.3460.676 0.681 0.684 0.653 0.667 0.684 0.671 0.652 0.600 0.647 0.595 0.2850.671 0.676 0.680 0.645 0.660 0.680 0.665 0.642 0.584 0.637 0.578 0.2230.665 0.671 0.675 0.636 0.653 0.675 0.659 0.633 0.568 0.628 0.560 0.1620.660 0.666 0.671 0.627 0.646 0.671 0.652 0.624 0.551 0.618 0.543 0.1000.654 0.661 0.667 0.618 0.639 0.667 0.646 0.615 0.535 0.608 0.526 0.0390.649 0.656 0.662 0.609 0.632 0.662 0.640 0.606 0.519 0.598 0.509 -0.023

2nd tier conditions

Appendix E

SUMMER WINTER SUMMER WINTERmin avg max min avg max clear mild cloudy clear mild cloudy

0.696 0.698 0.700 0.686 0.692 0.700 0.694 0.686 0.664 0.684 0.661 0.5290.691 0.693 0.695 0.678 0.685 0.695 0.688 0.677 0.648 0.674 0.644 0.4680.685 0.688 0.691 0.669 0.679 0.691 0.682 0.668 0.631 0.664 0.627 0.4070.680 0.684 0.686 0.660 0.672 0.686 0.675 0.659 0.615 0.655 0.610 0.3450.674 0.679 0.682 0.651 0.665 0.682 0.669 0.650 0.599 0.645 0.593 0.2840.669 0.674 0.678 0.643 0.658 0.678 0.663 0.640 0.582 0.635 0.576 0.2230.663 0.669 0.673 0.634 0.651 0.673 0.657 0.631 0.566 0.626 0.559 0.1620.658 0.664 0.669 0.625 0.644 0.669 0.650 0.622 0.550 0.616 0.542 0.1000.652 0.659 0.665 0.616 0.637 0.665 0.644 0.613 0.533 0.606 0.524 0.0390.647 0.654 0.660 0.607 0.631 0.660 0.638 0.604 0.517 0.597 0.507 -0.022

3rd tier conditions

30 40 50 60 70 80 90100

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0.5500.6000.6500.7000.750

Winter

minavgmax

Ti-Ta (°F)

Efficie

ncy