Solar hot water sizing

Introduction

Visible light (insolation) is the major power resource accumulated by systems that administer area heat, water heat, and also power for dwellings. Because of the Earth�s axial tilt, the amount of solar insolation event at any one spot on the Earth�s surconfront varies throughout the year. On a everyday and also a seasonal basis, the amount of light power incident on a surconfront varies from sunclimb to suncollection. The atmospheric problems and elevation at the site are additionally components that affect the amount of light getting to the Earth�s surface.

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For sites above and also below the equator, seasonal variations are frequently marked by the spring and fall equinoxes and also the summer and winter solstices. The equinoxes are characterized as the moment of year when the sunlight crosses the equator (March and also September 21/22). At this time there are an equal variety of hours of daylight and nighttime. The summer and also winter solstices are identified as the moment as soon as the sun reaches its highest/lowest latitude. In the north latitudes, the summer solstice in June 21/22 and the winter solstice is December 21/22. The summer solstice is the date when the variety of daylight hrs is the longest and also the winter solstice has the shortest number of daylight hrs. In the southern hemispbelow, the solstices are simply the opposite.

Before installing a solar water-furnace, you should first take into consideration the site"s solar reresource, given that the performance and style of a solar water-heater depend on just how a lot of the sun"s energy reaches the structure website. You�ll likewise have to properly size the system to encertain that it meets the hot-water demands of the house. In this leschild, you will learn just how to site and dimension a solar water-heater.


Energy Calculations and also Units

We need to be able to measure and compare energy and various other quantities to be able to estimate the dimension of solar water-heating and also solar electrical devices. We, therefore, have to acquire an understanding of the power calculations and also power devices we use to make these approximates.

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Convariation Table

Definitions:

Heat: British Thermal Unit (Btu): the amount of energy to raise 1 pound of water 1 degree Fahrenheit

Therm: 100,000 Btu

DekaTherm (DKT): 1,000,000 Btu Natural gas contains about 1 DKT of energy in 1000 cubic feet of gas.


Electric Power and Energy 1 Watt = 1 Volt*1 Amp in pudepend resistant circuits

1000 Watts = 1 Kilowatt (KW) (this is Power)

1 KW* 1 Hour = 1 Kilowatt-Hour (this is energy)

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Siting a Solar Water-heating System

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Geographic orientation and collector tilt have the right to influence the amount of solar radiation the device receives.

Solar water-heating systems use both direct and diffusage solar radiation. Regardless of being a chillier, northern climate, Pennsylvania still provides an enough solar resource. Generally, if the installation site is un-shaded from 9 a.m. to 3 p.m. and encounters southern, it"s an excellent candidate for a solar water-heating system.

PVWatts (www.pvwatts.org) is a beneficial on-line calculator that helps to understand the solar resource at a provided place. The table listed below shows average summer, winter, and also annual solar radiation for Wilkes-Barre, Pennsylvania. PVWatts have the right to assist you recognize the solar resource easily accessible at your specific site, and additionally assist you estimate the dimension of solar mechanism needed to provide the important solar power for either solar water-heating or solar electrical units. (Tip: To transform from Kilowatt-hrs to Btu, multiply by 3413. To convert square meters to square feet, multiply by 10.76).

Average Daily Solar Radiation for the months of January and July and also yearly for assorted tilts and also azimuth angles in Wilkes Barre, PA (kWh/m2/day) Source: PV Watts Webwebsite www.pvwatts.org

Tilt Angle Azimuth Angle January July Yearly
25 180 2.50 5.58 4.19
25 210 2.40 5.81 4.12
25 270 1.72 5.52 3.59
40 180 2.81 5.47 4.19
40 210 2.66 5.45 4.09
40 270 1.69 5.08 3.37
55 180 2.89 4.82 3.98
55 210 2.79 4.85 3.88
55 270 1.62 4.55 3.09

Collector Orientation Collector orientation is instrumental in achieving maximum performance from a solar energy system. In general, the optimum orientation for a solar collector in the north hemisphere is true southern (azimuth of 1800). However, recent researches have actually displayed that, relying on the place and also collector tilt, the collector deserve to confront up to 90� east or west of true south without significantly decreasing its performance.

Local climatic problems have the right to play a significant function in whether to orient the collectors eastern or west of true south, as well as in determining the proper tilt angle for the collectors. The building�s roof orientation and slope, shading components, regarded aesthetics, and local covenants also play considerable duties in the installation of the solar system�s collection hardware.

You must also consider factors such as roof orientation (if you plan to mount the collector on the roof), regional landscape features that shade the collector everyday or seasonally, and neighborhood weather conditions (foggy mornings or cloudy afternoons, for example), as these factors likewise can impact the collector"s optimal orientation.


Collector Tilt Most residential solar collectors are level panels that deserve to be installed on a roof or on the ground. Called flat-plate collectors, these are typically addressed in a tilted position associated to the latitude of the area. This enables the collector to ideal capture the sun. These collectors have the right to usage both the direct rays from the sunlight and reflected light that comes through a cloud or off the ground. Due to the fact that they usage all obtainable sunlight, flat-plate collectors are the ideal alternative for many northern states.

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Optimal tilt angle for solar collector is an angle equal to the latitude.

Although the optimal tilt angle for the collector is an angle equal to the latitude, mounting the collector level on an angled roof will certainly not bring about a big decrease in system performance and is often preferable for aesthetic reasons. You will, yet, desire to take roof angle into account when sizing the system.


Shading As aforementioned, solar collectors must be mounted at a site that is un-shaded from 9 a.m. to 3 p.m. and also encounters southern. Shading from hills, trees, structures, and also various other geographical features can substantially mitigate the collectors� performance. Before installing a solar power mechanism, you need to first complete a sun route diagram to estimate the affect of shading on yearly system performance.

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Sizing a Solar Water-Heating System

To appropriately dimension a solar water-heating system, you�ll have to identify the total collector location and the storage volume essential to meet 90 to 100 percent of the household"s warm water demands in the time of the summer. One software program tool that is available to calculate solar water furnace sizing is RetDisplay (www.retdisplay screen.net/ang/home.php). If you plan on making a variety of solar water heaters, you deserve to pick to downpack the Solar Hot Water software application from www.retscreen.net/ang/t_software application.php. This software program deserve to be used to dimension solar water-furnaces, and we will certainly use it to verify our �Rule of Thumb� calculation example listed below.

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Sizing Collector Area A great ascendancy of thumb for sizing collector area in north climates such as Pennsylvania is to permit 20 square feet (2 square meters) of collector area for each of the first two family members, and also 12 to 14 square feet for each additional person.


Sizing Storage Volume A tiny (50- to 60-gallon) storage tank is typically sufficient for one to two civilization. A tool (80-gallon) storage tank works well for 3 to 4 people. A huge tank (120-gallon) is correct for four to 6 civilization.

For energetic solar water-furnaces, the size of the solar storage tank increases via the dimension of the collector�commonly 1.5 gallons per square foot of collector. This helps proccasion the system from overheating when the demand for hot water is low.

The Solar Rating and also Certification Corporation webwebsite has thermal performance outcomes for tested solar collectors at www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htm. The website has performance data within the temperature variety that is correct for picking a collector for heating the hot water demand. The following is a page from this website. Bear in mind that these collectors are certified based upon Florida problems. A trial and also error procedure is vital to acquire to the ideal collector sizing for Pennsylvania.


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Collector Certification (A)

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Collector Certification (A)


Collector

Glazing

Absorber

Gross Area

Thermal Performance Intermediate Temperature Rating

Manufacturer

Model

FSEC #

No.

Type

Material

Coating

Sq. Ft

Btu/Day

Btu/ft²

ACR Solar International Corp

Skyline 20-01

00030

1

Clear rigid plastic

Copper tubes and also fins

Selective

20.07

14800

736

ACR Solar Internationwide Corp

Skyline 10-01

00212C

1

Clear rigid plastic

Copper tubes and also fins

Selective

10.00

7500

747

AMK-Collectra AG

OPC 10 MK-III

00083

1

Evacuated glass tube

Copper tubes and aluminum fins

Selective

15.67

12500

800

Alfa Casting Corp

*AC-419

83128

1

Glass

Copper tubes and aluminum fins

Nonselective

18.41

14200

770

Alfa Casting Corp

*ACC-419

83129

1

Glass

Copper tubes and also fins

Nonselective

18.41

16400

893

Alternative Energy Technologies, LLC

AE-21

00081N

1

Glass

Copper tubes and fins

Selective

20.77

17600

849

Alternate Energy Technologies, LLC

AE-26

00088N

1

Glass

Copper tubes and fins

Selective

25.35

21700

856

Alternative Energy Technologies, LLC

AE-32

00089N

1

Glass

Copper tubes and fins

Selective

31.91

27500

862

Alternate Energy Technologies, LLC

AE-40

00090N

1

Glass

Copper tubes and also fins

Selective

39.79

34400

866

Alternate Energy Technologies, LLC

AE-32-E

00036C

1

Glass

Copper tubes and fins

Moderately selective

31.85

22300

701

Alternative Energy Technologies, LLC

AE-40-E

00037C

1

Glass

Copper tubes and fins

Moderately selective

39.71

27900

704

Alternative Energy Technologies, LLC

ST-32E

00119C

1

Glass

Copper tubes and fins

Moderately selective

30.91

22900

742

Alternating Energy Technologies, LLC

ST-40E

00120C

1

Glass

Copper tubes and also fins

Moderately selective

38.62

28400

735

Alternate Energy Technologies, LLC

MSC-21

00213N

1

Glass

Copper tubes and also fins

Selective

21.50

17400

810

Alternating Energy Technologies, LLC

MSC-32

00214N

1

Glass

Copper tubes and fins

Selective

32.67

27200

833

Alternative Energy Technologies, LLC

MSC-40

00215N

1

Glass

Copper tubes and fins

Selective

42.15

35100

833

Amerihave the right to Solar Netjob-related, Ltd.

ASN30A

89011

1

Clear rigid plastic

UV Stabilized EPDM

None

31.17

21100

676

American Solar Netjob-related, Ltd.

ASN45A

89018C

1

Clear rigid plastic

UV Stabilized EPDM

None

46.50

31600

680

Amerideserve to Solar Netoccupational, Ltd.

ASN60A

91025C

1

Clear rigid plastic

UV Stabilized EPDM

None

61.83

41600

673

Apricus Solar Co., Ltd.

AP-10

00202N

1

Evacuated glass tube

Glass cylinder

Selective

14.45

8500

589

Apricus Solar Co., Ltd.

AP-20

00106N

1

Evacuated glass tube

Glass cylinder

Selective

29.16

17300

594

Apricus Solar Co., Ltd.

AP-22

00203N

1

Evacuated glass tube

Glass cylinder

Selective

32.11

19100

594

Apricus Solar Co., Ltd.

AP-30

00204N

1

Evacuated glass tube

Glass cylinder

Selective

43.63

27600

636

Aqua Sol Contents Ltd.

6536

00068

1

Glass

Copper tubes and aluminum fins

Nonselective

36.46

Thermosiphon System Net Energy Delivered: 27,300 Btu Heat Loss Coefficient: 3.7 Btu/hr°F

*The flow price through a solar collector affects its performance, yet may or may not influence the performance of the device in which it is mounted. Several of the collectors provided right here have been tested at flow prices other than those stated by trial and error standards. These collector models are determined via an astethreat (*) instantly preceding the version number.


Comparing the day-to-day hot water warm demand also through the tested collector thermal performance numbers, we desire to select solar collectors that will produce the 45,081 Btu/day. Looking in the Btu/day column, we see that we will certainly require 2 collectors to match our load, each collector being able to administer about 22,541 Btu/day. An Alternating Energy Technologies AE-32 collector is rated at 27,500 Btu/day. These collectors each have actually a room of cshed to 32 square feet. This instance compares favorably via the general guidelines presented previously for the number of solar collectors to install � 20 square feet of collector area for the initially two human being and also 12 square feet for each added occupant.

For Pennsylvania, the water storage tank to couple to 64 square feet of solar collector have to be at least 80 gallons, yet a tank via a capacity of 90+ gallons would certainly be much better.

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Questions

Using the data for Wilkes Barre in the table above, what is the percent distinction in the yat an early stage average daily solar insolation event on a surchallenge facing true southern (azimuth angle 1800) via a tilt of 25 degrees versus that with a 55 level tilt? For a 25-level tilt versus a 40-level tilted surface? What is the percent difference between the yearly average value for a surface tilted at 25 degrees facing true southern versus the exact same surconfront, very same tilt yet via an azimuth angle of 210 degrees? What is the percent difference in between the yearly average value for a surconfront tilted at 25 degrees dealing with true south versus the exact same surconfront, same tilt via an azimuth angle of 270 degrees? For surencounters with 40 and also 55 level tilts? Given the percent differences displayed in question 3, which tilt angle is more reasonable to accept if you had actually no choice but to install a solar device via an azimuth angle of 270 degrees? Please define your answer. If you stayed in Wilkes Barre and also wanted to maximize the collection of solar insolation in the winter, what tilt and azimuth angles would certainly you mount the solar collectors? Conversely, if you wanted to maximize the summer solar arsenal, what tilt and also azimuth angles would certainly you mount the solar collectors? In the solar mechanism sizing instance, the total everyday heat energy demand also for 80 gallons of warm water was calculated at 45,081 Btus. What would certainly the total warmth power demand be for 80 gallons through the warm water temperature set at 1400F with the same cold water temperature? What would certainly the auxiliary energy demand also be for 80 gallons of warm water via the warm water temperature collection at 1200F and a solar water heater offering 1000F water to the cold water inlet of the typical domestic hot water heater? Assume the warm losses for the 120 degree set temperature from the standard heater as soon as making the calculation.

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