this page is not complete. it is a pooling place for research at the moment. much of this information has been copied verbatim and may be copyrighted. it will not remain in its current form for long

Abstract

This project examines two hot water heating systems that are commonly used on residential buildings; Solar Thermal Collectors and Air source Heat Pumps. A spreadsheet comparing factors such as system cost, efficiency, operating costs, maintenance and pollution has been created. Values in the spreadsheet can be changed to produce a comparison answer that is more closely based on any user’s needs. Pre selected options in the spreadsheet are based on stated assumptions and are the baseline for comparison. The conclusion of this project has determined that the optimum hot water heating system varies depending on water use needs. For low water consumption, heat pumps are more cost effective. For higher water consumption, solar thermal panels are the more economical choice. Both systems are effective at reducing the consumer’s carbon footprint.

Group members: Adam Channal, Devan Hemmings, Ryan Kriken, Robert Duncan

Background

A homeowner in coastal Humboldt County, CA has an aging domestic hot water system, and would like to replace it with a more environmentally responsible system. Basing his decision on a set of criteria, the homeowner will choose to install either a solar thermal water heating system or an air-source heat pump. Adam Channel, Robert Duncan, Devan Hemmings and Ryan Kriken have been hired as consultants to research different hot water systems and provide a comparison of these two technologies. The client has expressed a desire to know the prices of different systems, their efficiency, lifespan, buyback time, maintenance needs, and energy costs for using the system. To simplify the client’s decision, a spreadsheet allowing for changes to various inputs has been created. This spreadsheet allows for changes to variables such as system manufacturer, climate data, household water use, and several other variables to tailor the system to the client’s needs.


What is a Heat Pump?

A heat pump is any device which moves heat from one location to another. Heat pumps operate much like a refrigerator, only in reverse. A refrigerator pumps a refrigerant through a compressor and transfers heat from inside the cooled space to the outside ambient air thus cooling the inside of the fridge. A heat pump on the other hand takes heat from the outside and uses it to heat the inside air or takes inside or outside air to heat water.

There are two types of heat pumps: ground source heat pumps, and air source heat pumps. Either of these types can be used to heat a home or to heat water or both. We chose to do our analysis on air source heat pumps.

Ground source heat pumps basically work by circulating refridgerant through underground pipes and back through a compressor where it is vaporized, and condensed causing it heat up and then the heat is transferred to a coil where it can be utilized for home heating or water heating purposes. The reason the pipes are run underground is to utilize the consistent 58 degree Fahrenheit ground temperature which in cold climates may be higher than the average air temperature. Also, many air source heat pumps become very inefficient below 40-50 degrees F and in very cold climates will stop working. Ground source heat pumps can also be used as air conditioners in the summer months and are more cost effective when used to heat and cool a home. An attachment to this type of system, called a desuperheater, can be attached to also provide the home with hot water. We did not do an analysis of the desuperheater due to the very high installation costs of groundsource heat pumps.

Air source heat pumps can be used either to heat the air or water. For home heating uses there is generally an outside unit with a fan and condenser drawing heat from the outside air, and inside unit with a fan, condenser, compressor, and heat expansion valve, and pipes running in to circulate the heat to and from the inside environment.

For air source heat pump water heaters, the heat from the ambient air is pulled with a fan into the condenser and heat is transferred into the water tank and heats the water through a coiled heat exchanger. Because heat is being moved instead of generated, a heat pump water heater can be up to about 60% more efficient than traditional electric water heaters.

Air source heat pump water heaters come as either a prepackaged unit which includes a tank, and an electric component heating unit, or as a stand alone unit that can be hooked into a preexisting water heater tank. For our project we chose the GE hybrid heat pump water heater because it had the highest energy factor efficiency rating and the installation and unit cost was fairly low compared to  units that don't come as a package.

Because a heat pump is taking heat from the air around it, Heat pump water heaters require installation in locations that remain in the 40º–90ºF (4.4º–32.2ºC) range year-round. Garages, cellars, laundry rooms, or basements are ideal locations for installation. It is not recommended, however for a unit to be installed in a heated room because they tend to cool the air around them. It is also best not to have a unit installed outside due to problems with weather corrosion, and temperatures below 40 F. It is recommended that at least 1,000 cubic feet (28.3 cubic meters) of air space is in the room around the water heater.

What is Solar Thermal?

Solar-thermal water heating.gif

Solar thermal water systems use energy gathered from sunlight to heat water. Sunlight falls on collector panels which is then moved to a hot water tank similar to conventional tanks. Many types of solar thermal systems exist some of which are more adapted to small scale and therefore residential use. The systems examined below can be adapted to fit either small scale or large scale water needs. Other systems such as parabolic solar collectors tend to be used for large scale collection and are not examined in this project.


Almost all residential Solar Thermal systems fall in to one of the following two types of systems:

Open Loop systems take water from local water pipes, pass it through the solar thermal panels to then be used directly for hot water. A schematic of such a system can be found to the right.

Closed Loop systems circulate a coolant/water through the solar thermal panels and transfer the heat using a heat exchanger to your hot water tank. In this system, the water from the tap stays in your water heater while it is being heated and does not travel through the solar thermal panels. A schematic of this system can be found to the right.


The two collector panel technologies examined in this project are:


Solar thermal panel.png

Evacuated Tubes are layered glass cylinders that absorb sunlight and heat water in the center tube which is in a vacuum. The lack of pressure inside to tubes allows the boiling of water at a much lower temperature. Heat from the boiling water in the tubes is transferred to another liquid. This heated liquid travels through a house to a heat exchanger near/in the water tank. The heat exchanger again moves the heat out of the liquid and in to the water in the tank.


Flat-plate-solar-thermal-collector-119172.jpg

Flat Plate Collectors are sealed rectangular boxes with heat absorbing metal sheets next to small tubes of water or coolant. This liquid is moved through the house to the heat exchanger near/in the water tank. A schematic of this system can be found here.


How is a Solar Thermal System set up?

1.Size a system for house (depends on number of people and hot water needs) Generally, 80 gall tanks are sufficient for households with 3-4 people. Areas with less sunlight will need greater collector size. Sizing varies based on climate and hot water needs but a general rule of thumb according to Vermonts'  Renewable Energy Resource Center is about 0.7ft2 and 0.85 ft2 of collector area per gallon of storage. Vermont RERC

2.Determine type of solar thermal system (flat plate vs. solar thermal...or another system!)

3. Determine whether you want an open loop system or a closed loop system. Open loop system have the benefit of less heat lost in transfering. Open loop systems can only use water as the liquid passing through the panels is the water coming out of your hot tap. Closed loop systems are not subject to mineral deposits from municipal water sources. Closed loop systems can use water or coolant.

3. Determine if you want to keep current water heater and purchase external heat exchanger or replace with tank that has an internal heat exchanger. If you are replacing your tank, it is often cheaper to by the internal heat exchanger (tank and exchanger are one unit) instead of purchasing two seperate units that then have to be connected.

4. Choose to either install the system yourself or hire a contractor. Unless you have plumbing experience and are able to build these systems in accordance with local building codes, it would be advisable to hire a contractor to continue the job from here. The rest of these instructions will help you be an educated consumer...

5. Determine the optimum placement for the panels. This can be on your roof (ususally the best spot) or any other convenient location. In the northerrn hemisphere, south facing panels maximize sunlight exposure even during winter months when the sun is low in the sky. Be sure to maximize your solar window (the angular range of direct sunlight the panels receive during the day) and angle the panels equal to your latitude (40 degrees latitude-- 40 degrees angle towards south). Panels can be mounted on angled rooftops or on mounting racks for flat rooftops.Several appropedia pages such as Solar Radiation Maps and Solar Water Heating further discuss methods of determining the amount of light available for collection. 

6. Select and purchase a hot water tank/heat exchanger system.

    a. If you are keeping your old hot water tank you must purchase an external heat exchanger. The Piggyback system used in the spreadsheet is an external heat exchanger.

    b. If you are purchasing a new hot water tank you can decide to have an internal or external heat exchanger. Internal heat exchangers come as a part of the water tank ( a single unit) external heat exchangers are sold seperately from hot water tanks(exchanger and tank two seperate units). Depending on your needs, you may choose one system over the other.

7.Determine if you require a freeze protection system such as a drainback tank. If temperatures in a clients region drop below 40 degrees F, there is a potential for water to freeze in the system; This can cause extreme damage to a solar thermal system and create maintenance nightmares. To prevent water from freezing in the panels drainback systems such as the one desrcibed below must be installed.

     During night time when the solar panels are not receiving any light (and therefore heat), the water from the panels drains down in to a small tank inside the protection of the house. This prevents water from freezing in the pipes on your roof and potentially bursting any connections or cylinders. If you live in a climate that experiences any had frosts, a drainback system is required. Several options for powering the drainback system are avaialable. A simple low flow water pump can be plugged in to the socket that turns off at night using a simple timer; or a small photovoltaic panel can power a pump(this system is nifty because during the nighttime when there is no sun hitting pv or thermal panel, pump shuts off and let water fall back in to drainback tank-fully contained!!!).

8.Set up the piping. Try to find the shortest and easiest route through your house. A longer distance means more heat lost in transit and higher material costs.

9. Determine the heat transfering liquid.

   a. If an open loop system has been selected, the heat transfer liquid must be municipal water.

   b.If a closed loop system has been selected, the heat transfer liquid can be water or coolant. Coolant costs more than water but will not leave any mineral deposits in the system. Distilled water can actually leech minerals from the system and is not prefered.

10.Connect the pieces and let'er rip! The panels should start working when they first receive light.

Problem statement

The final goal is to compare these two technologies for their ability to heat water for residential needs. The main questions we hoped to answer are;

-Can these systems supply all hot water needs? If not what percentage can they supply? Embedded in this question is, how much energy will a consumer save by installing these systems?

-Which system will cost the consumer less upfront and over time?

-Which system will last longer?

-Most importantly, what are the variables that make each of these systems an economical and environmentally friendly choice for consumers?


This spreadsheet will compare variable types of solar thermal collectors (flat plate and evacuated tubes) to air source heat pumps for heating domestic water needs. The client will enter in the following information:


   •  Latitude of Clients location, # of sunny days, # of partly cloudy days, # of cloudy days

   • Household data

     o Number of people per house

      o Appliances; dishwasher and laundry machine use frequency
      o Showering/Bathing time
      o Desired temperature for water tank
      o Current hot water tank; cost, efficiency, life cycle, energy factor (for comparison to new systems)
   • A solar heat pump model to compare
      o Solar collector model/manufacturer
      o Heat Transfer/water tank model/manufacturer
   • A Heat Pump model to compare
   • Desired Life cycle analysis length in years

Upon entering these specific variables for the client, information regarding each system, assumed water use, climate data and system components will appear in the spreadsheet. The assumptions and conversions used can be found to the right of the spreadsheet on the main page. Several tables with the data exist on subsequent sheets and can be used to add more options to the spreadsheet.
Based on data we found in our research and the user entered data the spreadsheet will return results comparing the following points:


The Bottom Line output

Annual energy costs to consumer after installing a solar thermal system or a heat pump system

Amount of money saved per year compared to using a conventional waterheating system

Payback time in years for a solar thermal system or a heat pump system

CO2 emissions in tons per year for water heating needs with a new system installed

Mercury emissions in grams per year for water heating needs with a new system installed

Life cycle cost over a yearly length


Additional outputs will show up on the spreadsheet. All variable outputs have been embedded in to the Bottom Line Output.




Instructions

If your excel sheet has thorough instructions, the instructions in the writeup can be brief and refer to the excel (and use a screenshot or two), otherwise, be very specific (and use screenshots). Make sure to link to your spreadsheet here.

These are the instructions for using the spreadsheet. **it may be helpful to print these instructions to view next to the spreadsheet.**

1.Select the latitude of clients location.(-90 to 90)

2.SEnter the number of clear days per year, Enter the number of partially cloudy days per year, and enter the number of cloudy days per year. These three numbers should total 365 days. A note beneath the boxes will note when the total is 365.

3. Select the number of people in the household.(1-10)
4. Select yes/no for a dishwasher.
5. Select yes/no for a laundry machine. If yes, go to 6, If no go to 7.
6. Enter number of laundry loads per person per week.
7. Select yes/no for taking baths.
8. Select yes/no for taking showers shorter than 5 minutes. If yes, skip to 8, if no go to 7.
9. Enter average time of shower.
10. Enter the average water temperature(F) coming out of municipal water pipes.
11. Enter preferred temperature(F) for water heater.
12. Select the desired type of new water heater.**
13. Select a type of solar thermal system to compare.
14. Select a model of solar thermal system to compare.
15. Select yes/no for purchasing a new water heater tank.
16. Select a life cycle length to analyze the systems.
17. Compare the annual price per system, annual emissions, and payback time for a solar thermal system or an air source heat pump!

    • The trendsetter contender is a heat exchanger and water tank combo. It is an automatic yes to be purchasing a new water tank. The cost of heat exchanger is in cost of tsetter contend., we need to make sure it isn’t counted twice.

Justification of assumptions

This section is a reference, thorough justification of your assumptions and values. Use references you gained during your literature review to back these up. Using automatic references [1] in this section is best.

Assumptions
Values

Source

Average milligrams of Hg/kWh
0.012
Energy star pdf CFL's and mercury table 1Energy Star
Average lbs of CO2/ kWh(coal)
2.117
Dept. of Energy 1999 CO2 emissions by energy type EIA CO2 report
Average lbs of CO2/ kWh(petroleum)
1.915
Dept. of Energy 1999 CO2 emissions by energy type EIA CO2 Report
Average lbs of CO2/ kWh(natural gas)
1.314
Dept. of Energy 1999 CO2 emissions by energy type EIA CO2 Report
U.S. dollars/ kWh
0.12
U.S Energy Information Administation
U.S. dollars/therm
0.98
adams pge bill…u.s.?
Maximum solar Thermal efficiency??
70%

natural gas water heater efficiency??
58%
where is this from, go
gallons used per faucet minute
3
common faucet maximum flow rate
gallons used per dishwasher load
8
Average for old dishwashers pre1994,non-energy star Energy Star Q&A
gallons used for bath
40
volume of 1/2 full short length bath or 1/4 of full length bath (L*W**H*7.5= ft3 to volume in gallons)
gallons used per shower minute
2.5
Most shower heads max at this flow rate, pre-1992 heads were greater Energystar Q&A
gallons used per laundry load

40

Low efficiency:40 high efficiency:28 EPA Water Challenge





asdf

Results

Describe overall concrete results based upon assumptions. Use graphs throughout the results section.


Graphical representation of each metric



A subsection/title for each metric

Describe the results for each metric based on specific assumptions. Use graphs throughout the metric result subsections.

Conclusion

The answer to our question, Which type of system should we suggest to a client? Our favorite answer: It depends! Certain conclusion can be found below; These are based on Humboldt County sunlight values and all of our assumptions. Please see the assumptions table earlier in this page and the assumptions table in the excel spreadsheet.

If you use less than 25 gallons of hot water per day, it is cheaper over a 30 year period to use air source heat pumps. This means you will need to replace the heat pump once (lifespan off 15 years so 30 years needs two heat pumps).
If you use more than 25 gallons of hot water per day, it is cheaper over a 30 year period to purchase and install a solar thermal system. The lifespan of this system is about 30 years but costs about twice as much upfront.

This is a very broad based conclusion but through our data it seems like air source water heaters would be more applicable in the settings of a single apartment with limited space and smaller water use. The solar thermal system would be more applicable in a four or more person house that uses more water and has more space for the system. It seems that for households in-between these two extremes it would be best to fill out the excel spread sheet we created so that the needs of the client can be better quantified.

Broad conclusion: For low water use households such as single person dwellings or water conscious users, heat pumps appear to be a very smart decision. However, high occupancy homes and high water use needs would be most positively impacted by solar thermal systems.

Discussion

What assumptions change the results the most? What are you surprised by? Whereas conclusions are concrete and quantitative, discussion is more qualitative.

Heat Pump

GE Air Source Heat Pump

The GE air source heat pump was chosen for this project because it had a high energy factor and for its easy installation. The installation of the GE air source heat pump is exactly like a regular water heater and costs about $400 dollars for professional installation. The GE unit switches automatically from four different settings. For most of the time it will be in eheat setting which means that only the air source heat pump is working. When a the water usage goes above the peak demand of 63 gallons it goes into hybrid mode which is the air source heat pump and the standard hot water heating component working as one to keep up with demand. There is a standard electric mode in which it works like a regular electric hot water heater and a high demand mode for households with higher than average water use. In this mode the electric hot water heater is working very hard.

We decided to stay away from air source hot water heater add on units. These units add on to existing electric water heaters. We decided to stay away from the add on units after a talk with Maples Plumbing in Eureka. According to Maples Plumbing it doesn’t make sense to buy these units because although upfront they are about half the price of the combined air source hot water heater unit, they have a high cost in installation. These attachable air source heat pumps also have a lifespan of 20 years, and the tanks on the electric water heaters have a life span of about 10 to 15 years. So the limiting factor is the electric hot water heater tank. Unless a person just installed a new electric hot water heater this technology wouldn’t be practical according to Maples Plumbing.

It is important to note in the final cost of the air source heat pump we did inlude a tax rebate from the Federal government. this rebate comes back to the buyer when they fill out ther federal a tax form. Under the current tax rebate a person can obtain 30% of the cost of the unit and instalation up to $1500 dollars.

'Benifits of 'Air Source Water Heater
'Downsides to 'Air Source Water Heater
Lifespan as long as regular water heater (15 yrs)
Air temp must be above 40 degrees F for the heat pump unit to work
Instalation is like regular electric hot water heater
Less efficent under high constant demand for water
Little maintnance (filters changed once a month)
Needs to be in an inclosed area (cant be outside)
Federal tax rebate of 30% of cost of unit and instalation up to $1500
The room must be at least 10' x 10' x 7' or larger (because it draws in surounding air)
Reduces carbon footprint




Solar Thermal

Solar thermal panels work extremely well in very sunny climates and less so in cloudy climates. Systems capturing lots of light can supply most if not all of your hot water needs. Continuous cloudy days will cause your back up heater to be working more. There is a point where the solar thermal system doesn't get enough sunlight every day to heat very much of your water. This means that the cost of heating your water (using electric, gas or other source) will be inversely proportionate to the amount of sunlight you get. More sunlight= back up system working less, less sunlight=back up system working more. In the fog belt region of Humboldt County, CA, solar thermal panels have a long buyback time (years it takes for water heating savings to accumulate to pay off entire cost of system). For other areas in humboldt county such as the more sunny mountainous regions (especially during summer months, winter months not so much) solar thermal system could play a larger role in water heating needs. Solar Thermal systems are ideal for heavy hot water loads. Multiple person houses would do well to choose solar thermal systems over air source heat pumps. Federal tax rebates are currently available for solar thermal systems. There are several qualifications that must be met in order to get the rebate. The requirements are as follows; at least half of all energy used in the dwelling must come from solar, the system installed must be SRCC certified and only costs on the solar thermal system are eligible for rebates. If your residence meets these requirements, 30% of the entire cost of the system can be refunded on your next federal tax bill. If the 30% rebate is greater than what you pay in federal taxes in the year of installation, 100% of your federal taxes are refunded to the purchaser.



Benefits of Solar Thermal System Downsides to Solar Thermal System
Long lifespan of system-30years Exspensive start up costs-approx.$4000-$5500
Easily expandable-more panels are easy to place in series Long buyback time in cloudier climates- about 20 years
Efficient for high water use Difficult to install without prior experience
No maintenance-system is self-sufficient (assuming no damage)
Much more complicated system than conventional water heaters
Energy self-reliance- reduces costs of heating
Doesn't provide 100% of water needs at high demand volumes or low sunlight










-why we chose a single unit air source heat pump water heater -what climates this system is best for -what hot water usage this is best for -the eheat setting compared to hybrid compared to other settings -different types of solar thermal systems -which ones make the most sense for humboldt -what would adam choose to put on his house -what we might do differently -other options besides solar or heat pump -combining systems

(adam) the amount of therms generated/year for the collectors needs to be fixed right now it is based off of kBTU/day values from the SRCC for differnt weather conditions and the climate data for the city selected. A better way to do it would be to find data for average amount of optimal sunlight hours/year for any given area and calculate with that but I couldn't find that data so I had to go off of the number of sunny/cloudy/mildly cloudy days per year from the National weather service. If I had more time I would find a better gauge of how much energy a collector generates/day in a given area. My guess is that the energy collected/year by the different collectors is lower in the spread sheet than it actually is and it throws off the comparison.

Steps to Improve Spreadsheet

Describe things to change and ways to expand the model.


-The values for sunlight per latitude do not take in to account the seasonal changes. In areas that get very little sunlight during winter months (winter in northern hemisphere) the back up system will be working the majority of the time. During summer months in high latitude areas, continuous sunlight for many hours every day will heat water needs well above what the household will use. The total amount of sunlight hitting the panels does not directly equate to how much water heating costs will be taking in to account seasonal variation.There needs to be a way to equate the seasonal differences. In extremely cold climates, these sytems become innappropriate due to low collection rates and excessive costs using a back up system. There is a threshold around 60 degrees latitude where the winter months have too little sunlight for thermal systems to provide any input of heat. Any system not being used for portions of the year might not be the most economical solution.

-Pollution from system manufacture: We did not examine the materials and production externalities from thesee two systems. The heat pump requires replacement every 15 years where as solar thermal replaced every 30 years. Dont know pollution externalities, recycling potential of materials

-Ground source heat pumps were not examined in this project. They are another type of heat pump that is commonly used for hot water heating. High installation costs with this system

 -Climate variation could be a little more concrete- it was difficult to find consistent sunlight values for regions, we just used NOAA national weather service values, they seemed most consistent

-Other types of hot water heaters could be included: On-Demand water heaters could be coupled with either of the examined systems

-Cost outputs could incorporate federal and state tax rebates. This was just mentioned in the conclusion


 


References

our google docs pages http://docs.google.com/Doc?docid=0ATx1YA1QWCofZGcybWZucmZfOWc1cDlyZGR4&hl=en http://docs.google.com/Doc?docid=0ATx1YA1QWCofZGcybWZucmZfOGR4NHg3OWQz&hl=en

excel sheet http://spreadsheets.google.com/ccc?key=tmMC1WYTdRugHMIJhhTvosw

state incentives for solar http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=CA145F&State=federal&currentpageid=1&ee=1&re=1 http://www.dsireusa.org/incentives/index.cfm?re=1&ee=1&spv=0&st=0&srp=1&state=CA

sizing for a solar system http://www.fsec.ucf.edu/en/consumer/solar_hot_water/pools/sizing.htm

some solar resoure? http://practicalaction.org/docs/technical_information_service/solar_thermal_energy.pdf

california renewables portfolio http://www.cpuc.ca.gov/PUC/energy/Renewables/index.htm

eia energy outlook for 2009 http://www.eia.doe.gov/oiaf/ieo/world.html

Solar thermal energy applications http://www.appropedia.org/Solar_thermal_energy_%28original%29

Heat-Transfer Fluids for Solar Water Heating Systems http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12940

Solar Water Heaters http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850 Sizing a Solar Water Heating Systes http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12880

Solar Water Heater Energy Efficiency http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12900

Evaluating Your Site's Solar Resource for Solar Water Heating http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12870

Siting Your Solar Water Heating System's Collector http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12890

Notes from class presentation on solar thermal heating http://www.appropedia.org/Solar_Thermal_Panels

Solar Water Heating System Freeze Protection http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12960

southface.org

Heat pumps: Michael Winkler, here at RCEA: 7 >>zero << 7-269-1>>seven<<00 Solar thermal: Ben Scurfield, Scurfield Solar: 4>>four<<3-07>>five<<9 http://www.scurfieldsolar.com/ Alchemy Construction: http://www.alchemyinc.com/ Solar H2OT: http://www.solarhotwaterplus.com/index.htm Newsflash: we’re hosting a workshop tomorrow night by Solar H2OT on solar hot water systems, where you can get an introduction to one approach by a local installer. Here’s a link to the announcement: http://www.redwoodenergy.org/EventsDetail.asp?EventDate=10/14/2009&EventID=222&Rec=1&DateID=294 Dana Boudreau Operations Manager Redwood Coast Energy Authority 707.2>>six<<9.17>>zero<<0 www.redwoodenergy.org


Solar Radiation

The nature and availability of solar radiation

http://www.appropedia.org/Solar_thermal_energy_%28original%29

Solar radiation arrives on the surface of the earth at a maximum power density of approximately 1 kilowatt per metre squared (kWm-2). The actual usable radiation component varies depending on geographical location, cloud cover, hours of sunlight each day, etc. In reality, the solar flux density (same as power density) varies between 250 and 2500 kilowatt hours per metre squared per year (kWhm-2 per year). As might be expected the total solar radiation is highest at the equator, especially in sunny, desert areas. Solar radiation arrives at the earth’s outer atmosphere in the form of a direct beam. This light is then partially scattered by cloud, smog, dust or other atmospheric phenomenon (see Figure 1 below). We therefore receive solar radiation either as direct radiation or scattered or diffuse radiation, the ratio depending on the atmospheric conditions. Both direct and diffuse components of radiation are useful, the only distinction between the two being that diffuse radiation cannot be concentrated for use.


Solar Radiation Basics http://www.energysavers.gov/renewable_energy/solar/index.cfm/mytopic=50012

Solar radiation is a general term for the electromagnetic radiation emitted by the sun. We can capture and convert solar radiation into useful forms of energy, such as heat and electricity, using a variety of technologies. The technical feasibility and economical operation of these technologies at a specific location depends on the available solar radiation or solar resource. Basic Principles

Every location on Earth receives sunlight at least part of the year. The amount of solar radiation that reaches any one "spot" on the Earth's surface varies according to these factors:

  • Geographic location
    * Time of day
    * Season
    * Local landscape
    * Local weather.

Because the Earth is round, the sun strikes the surface at different angles ranging from 0º (just above the horizon) to 90º (directly overhead). When the sun's rays are vertical, the Earth's surface gets all the energy possible. The more slanted the sun's rays are, the longer they travel through the atmosphere, becoming more scattered and diffuse. Because the Earth is round, the frigid polar regions never get a high sun, and because of the tilted axis of rotation, these areas receive no sun at all during part of the year.

The Earth revolves around the sun in an elliptical orbit and is closer to the sun during part of the year. When the sun is nearer the Earth, the Earth's surface receives a little more solar energy. The Earth is nearer the sun when it's summer in the southern hemisphere and winter in the northern hemisphere. However the presence of vast oceans moderates the hotter summers and colder winters one would expect to see in the southern hemisphere as a result of this difference.

The 23.5º tilt in the Earth's axis of rotation is a more significant factor in determining the amount of sunlight striking the Earth at a particular location. Tilting results in longer days in the northern hemisphere from the spring (vernal) equinox to the fall (autumnal) equinox and longer days in the southern hemisphere during the other six months. Days and nights are both exactly 12 hours long on the equinoxes, which occur each year on or around March 23 and September 22.

Countries like the United States, which lie in the middle latitudes, receive more solar energy in the summer not only because days are longer, but also because the sun is nearly overhead. The sun's rays are far more slanted during the shorter days of the winter months. Cities like Denver, Colorado, (near 40º latitude) receive nearly three times more solar energy in June than they do in December.

The rotation of the Earth is responsible for hourly variations in sunlight. In the early morning and late afternoon, the sun is low in the sky. Its rays travel further through the atmosphere than at noon when the sun is at its highest point. On a clear day, the greatest amount of solar energy reaches a solar collector around solar noon. Diffuse and Direct Solar Radiation

As sunlight passes through the atmosphere, some of it is absorbed, scattered, and reflected by the following:

  • Air molecules
    * Water vapor
    * Clouds
    * Dust
    * Pollutants
    * Forest fires
    * Volcanoes.

This is called diffuse solar radiation. The solar radiation that reaches the Earth's surface without being diffused is called direct beam solar radiation. The sum of the diffuse and direct solar radiation is called global solar radiation. Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days. Measurement

Scientists measure the amount of sunlight falling on specific locations at different times of the year. They then estimate the amount of sunlight falling on regions at the same latitude with similar climates. Measurements of solar energy are typically expressed as total radiation on a horizontal surface, or as total radiation on a surface tracking the sun.

Radiation data for solar electric (photovoltaic) systems are often represented as kilowatt-hours per square meter (kWh/m2). Direct estimates of solar energy may also be expressed as watts per square meter (W/m2).

Radiation data for solar water heating and space heating systems are usually represented in British thermal units per square foot (Btu/ft2).


Solar Thermal

1.5 Pressure and Temperature Control Relief Valve

When a closed loop system is specified, the recommended pressure is 2 Bar, using a boiler filling check valve hose as the access point for passing water or a water/glycol mix into the circuit. Within the circuit, a pressure relief valve must be installed whereby any hot water release, due to over pressure, is safely evacuated. (tssp manual)

1.7 Freeze Protection

As an established solar thermal system design and supply business, we discourage the use of glycol as a freeze protection additive to the water in temperate climates. TrendSetter encourages systems in drainback configuration, as the drainback design is the most inherently freeze-resistant form of solar water heating. Where other configurations rely on propylene glycol or other compounds to resist freezing, the drainback configuration allows the collectors to drain automatically under gravity, with water being removed from outside weather conditions and remain protected within a superinsulated tank. TrendSetter does not guarantee its solar collectors against freeze related damage.

1.8 Collector Gross Weight (filled)

ST – 10 = 42.6 kg / 94 pounds ST – 22 = 88.2 kg / 194 pounds ST – 30 = 103.8 kg / 228 pounds

1.9 Wind Stress and Snow Loads


Please respect the relevant building codes and regulations with regards to the local climatic conditions and constraints concerning wind stress on attachment points and snow loads. The number of anchors and the supporting rack must be dimensioned in accordance with the collector type, the roof pitch, building height, maximum wind velocity and the standard snow load of the site. Standard frame kits are designed to withstand winds of up to 80 mph/128kp/h. It is the responsibility of the installation supervisor to check that the frame mounting is suitable. If the installation is within a proven high wind exposure area, please contact the supplier.

1.10 Hail Resistance

The high quality glass evacuated borosilicate tubes are able to handle significant impact stresses once installed. Substantial independent testing of these Borosilicate glass tubes produced in 1.8mm thickness has been carried out by well established testing institutions such as SPF (Switzerland) Fruehauf Institute in Freiburg, SRCC/Bodycoat in USA/Canada and testing facilities in Australia. In general the majority of installations in northern climates have an angle of 35-60 degrees, so are less susceptible to any damage from hail stones in sizes of 25mm (1 inch). When installed at lower angles, hail stones of 20mm (3/4 inch) are not a problem. In the unlikely event of a tube being broken, it can be easily replaced whilst respecting current building safety regulations. A damaged tube has little short term incidence on the overall heat performance of the collector. Tubes that have lost their vacuum turn white.

2.10.2 Evacuated Tubes

Be careful when handling the evacuated glass tubes, as they will break if knocked heavily or dropped. Wear gloves and safety glasses when handling broken glass. To dispose of a tube which shows the vacuum has been lost, remove all of the internal components (heat pipe and fins etc.) and fully enclose it within one of the boxes in which it was supplied. Use a hammer to break the tube from one end (within the box) into small pieces. Place this in a receptacle (not plastic bag) where it can be collected and disposed of safely by the refuse company. Try where possible to recover the aluminium transfer fins in good condition to re-assemble inside the two spare tubes, as heat fins are included in these tubes which are packed in the 12 tube/heat pipe boxes.


3. Maintenance Maintenance of the system is very easy and includes the following tasks 3.1 Cleaning Regular weekly or monthly rainfall has proven to keep the tubes clean, but if particularly dirty they may be washed with soapy warm water and dried with a soft cloth or a glass cleaning solution. If the tubes are not easily and safely accessible, high pressure water spray is also effective. If located in a climate of monthly hot and dry sunny weather, the dust collected on the tubes will diffuse sunlight and reduce overheating in summer months and is therefore not of concern.

3.3 Broken Tubes

If a tube is accidentally broken it should be replaced as soon as possible to maximise collector performance. The system will still operate normally even with a tube broken. Any broken glass should be cleared away to prevent injury. To replace a tube: a) Unclip the two part cup; reduce the pressure between the tube and the manifold casing by screwing down the adjuster inside this innovative TrendSetter designed cup holder. Wear gloves for protection in case of accidental glass breakage and lift the bottom of the tube from within the lower part of the cup. Then slowly pull the tube downwards from the casing ports until free. The heat pipe can be left in place while safely withdrawing the tube from the collector. b) Remove the heat fins from the glass tube and keep the fins straight and safe ready to be re-fitted. Dispose of the tube safely and then gently remove the heat pipe from its port socket in the manifold. Do not bend it. At the same time check that the sealing ring in the manifold casing is located in its correct position. c) Use one of the spare tubes left with the customer to re-install the tube, heat pipe and fins etc as per instructions given in this manual.


Sizing b) As a general rule the solar collector will have been sized to provide close to 100% of your summer hot water needs, which, depending on the location and hot water usage patterns, may result in between 45%-90% of your annual hot water energy needs. During winter, increased cloud cover and reduced solar radiation levels may result in solar contribution as low as 20%. This is normal.

10 year warrantee

Collectors may be installed in banks of up to10collectors in series (300 tubes maximum) and unlimited parallel-connected banks. Collectors can be used for both domestic and commercial applications.

home into the pocket. Function two, unlike the majority of tube heat pipe collectors sold across the world, where the heat pipe is sealed with a silicone plug, this design allows any build up of heat to escape, when ever there is a power, pump or controller failure during a very sunny blue sky

circulated through the solar collector on the roof. The water in the storage tank will gradually rise in temperature. The water will rise 15°F-20°F in temperature between the time the water enters the solar collector and the time it leaves the solar collector.

the water temperature entering the water heater. For example, if the cold water entering the water heater is 60°F, the water heater will require fuel to raise the incoming water from 60°F - 120°F (8,617 BTU per 100 gallons). If the entering water temperature were raised to 100°F the fuel consumption would be reduced by 2/3rds. The same 100 gallons of hot water would consume only 2,878 BTU’s

2.1. The Trendsetter water heating system is a drainback freeze protected system. In a drainback system, the water drains out of the collectors each time the solar pump turns off, leaving no water in the system to freeze. A solar hot water system needs to be installed correctly to insure high efficiency and most importantly, safe and reliable operation. The system can be modified to operate as a closed loop system filled with special non-toxic polypropylene glycol. This will require an additional heat exchanger in the bottom of the TrendSetter tank as well as a separate expansion tank to be mounted between the closed-loop heat exchanger and the collectors.

If the pump stops on a sunny day after reaching the high temperature limit or in the event of a power failure during a hot day, the system will drain down. This will create stagnation conditions meaning the header will reach temperatures in excess of 300ºF. This will not damage the system, as it is designed to withstand occasional stagnation. Once the pump restarts, water will flow into the collector header pipe pushing the air out and back into the tank. You may notice an initial rumbling as the slug of superheated water will flash into steam as it contacts the hot manifold. If you have not used elastomeric pipe insulation the insulation is likely to melt

5.1. Trendsetter suggests using a minimum of 1/2”id pipe for up to 60 tubes. The flow rate for a (2) 30 tube array is approximately 1.6 gallons per minute. This would result in 1 ft of head loss per 10 feet of pipe. If the pipe run is greater than 100 feet use larger diameter pipe. The pipe or tubing must be installed without “traps” that prevent complete draining of the tubing when the pump shuts off. For easy installation we recommend the ROARK flexible stainless steel tubing with a special thumping tool purchased or loaned from Trendsetter. The threaded brass compression fittings are designed to make the installation easier. Elastomeric insulation can be slid over the tubing before the ends are swaged onto the tubing.

5.2. If the solar is a closed loop with polypropylene glycol under pressure (>29 psi), pressure release valves, expansion tank and/or other pressure control devices must be installed. The solar loop must not be exposed to pressure exceeding 85 psi.


Solar Thermal

flat-panel collectors - consider either a drain-back or double-pump system.

evacuated tube technology,

- which apparently can better capture energy in a cloudy climate.
- For example, evacuated tube is likely a poor choice for non-tinkering folks who tend to travel, or for families where occupancy is about to change significantly (kids off to college etc).

Cost

First, we will examine the question of why one might choose solar energy over other forms to heat water. Solar energy is accessible almost anywhere. It is easily used for heating up water in a shower system. The cost of a solar shower system verses a gas heated or electrically heated system is far less. Looking at the Energy Star website provided by the EPA, one observes that water heating is typically the third largest energy expense in your home (after space heating and cooling). Water heating typically accounts for about 14% of your utility bill. One way to reduce water-heating costs would be to replace your old water heater with an alternative form of water heating such as solar energy. http://www.appropedia.org/CCAT_solar_shower


Building Codes, Covenants, and Regulations for Solar Water Heating Systems

To find out what's needed for local compliance, contact the following:

  • Your local jurisdiction's zoning and building enforcement divisions
    o Briefly describe your intended construction, asking for other relevant ordinances/codes that might be in effect. o Find out if there are any additional local amendments or modifications to the regulations in effect.
    oAsk how to determine whether you are located in a historic district, flood-plain area, or any other special category regulated by a government body.
    o Ask where you may find pertinent ordinances/codes (local library, government office, etc.).
    o Read pertinent sections of the regulations, making photocopies of information you wish to file for future review and design/installation analysis.
    * Homeowner's, subdivision, neighborhood, and/or community association(s)
    o Ask if they have any ordinances, provisions, or covenants that may affect the design and installation of the system. o Copy and file pertinent sections for reference.


class presentation
Heat Pump


Other

Reduce Hot Water Use for Energy Savings http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13050

You can lower your water heating costs by using and wasting less hot water in your home. To conserve hot water, you can fix leaks, install low-flow fixtures, and purchase an energy-efficient dishwasher and clothes washer. Fix Leaks

You can significantly reduce hot water use by simply repairing leaks in fixtures—faucets and showerheads—or pipes. A leak of one drip per second can cost $1 per month.

If your water heater's tank leaks, you need a new water heater. Install Low-Flow Fixtures

Federal regulations mandate that new showerhead flow rates can't exceed more than 2.5 gallons per minute (gpm) at a water pressure of 80 pounds per square inch (psi). New faucet flow rates can't exceed 2.5 gpm at 80 psi or 2.2 gpm at 60 psi. You can purchase some quality, low-flow fixtures for around $10 to $20 a piece and achieve water savings of 25%–60%. Showerheads

For maximum water efficiency, select a shower head with a flow rate of less than 2.5 gpm. There are two basic types of low-flow showerheads: aerating and laminar-flow. Aerating showerheads mix air with water, forming a misty spray. Laminar-flow showerheads form individual streams of water. If you live in a humid climate, you might want to use a laminar-flow showerhead because it won't create as much steam and moisture as an aerating one.

Before 1992, some showerheads had flow rates of 5.5 gpm. Therefore, if you have fixtures that pre-date 1992, you might want to replace them if you're not sure of their flow rates. Here's a quick test to determine whether you should replace a showerhead:

1. Place a bucket—marked in gallon increments—under your shower head.
2. Turn on the shower at the normal water pressure you use.
3. Time how many seconds it takes to fill the bucket to the 1-gallon (3.8 liter) mark.

If it takes less than 20 seconds to reach the 1-gallon mark, you could benefit from a low-flow shower head. Faucets

The aerator—the screw-on tip of the faucet—ultimately determines the maximum flow rate of a faucet. Typically, new kitchen faucets come equipped with aerators that restrict flow rates to 2.2 gpm, while new bathroom faucets have ones that restrict flow rates from 1.5 to 0.5 gpm.

Aerators are inexpensive to replace and they can be one of the most cost-effective water conservation measures. For maximum water efficiency, purchase aerators that have flow rates of no more than 1.0 gpm. Some aerators even come with shut-off valves that allow you to stop the flow of water without affecting the temperature. When replacing an aerator, bring the one you're replacing to the store with you to ensure a proper fit. Purchase Energy-Efficient Dishwashers and Clothes Washers

The biggest cost of washing dishes and clothes comes from the energy required to heat the water. You'll significantly reduce your energy costs if you purchase and use an energy-efficient dishwasher and clothes washer. Dishwashers

It's commonly assumed that washing dishes by hand saves hot water. However, washing dishes by hand several time a day can be more expensive than operating an energy-efficient dishwasher. You can consume less energy with an energy-efficient dishwasher when properly used and when only operating it with full loads.

When purchasing a new dishwasher, check the EnergyGuide label to see how much energy it uses. Dishwashers fall into one of two categories: compact capacity and standard capacity. Although compact-capacity dishwashers may appear to be more energy efficient on the EnergyGuide Label, they hold fewer dishes, which may force you to use it more frequently. In this case, your energy costs could be higher than with a standard-capacity dishwasher.

One feature that makes a dishwasher more energy efficient is a booster heater. A booster heater increases the temperature of the water entering the dishwasher to the 140ºF recommended for cleaning. Some dishwashers have built-in boosters, while others require manual selection before the wash cycle begins. Some also only activate the booster during the heavy-duty cycle. Dishwashers with booster heaters typically cost more, but they pay for themselves with energy savings in about 1 year if you also lower the water temperature on your water heater.

Another dishwasher feature that reduces hot water use is the availability of cycle selections. Shorter cycles require less water, thereby reducing energy cost.

If you want to ensure that your new dishwasher is energy efficient, purchase one with an ENERGY STAR® label. Clothes Washers

Unlike dishwashers, clothes washers don't require a minimum temperature for optimum cleaning. Therefore, to reduce energy costs, you can use either cold or warm water for most laundry loads. Cold water is always sufficient for rinsing.

Inefficient clothes washers can cost three times as much to operate than energy-efficient ones. Select a new machine that allows you to adjust the water temperature and levels for different loads. Efficient clothes washers spin-dry your clothes more effectively too, saving energy when drying as well. Also, front-loading machines use less water and, consequently, less energy than top loaders.

Small-capacity clothes washers often have better EnergyGuide label ratings. However, a reduced capacity might increase the number of loads you need to run, which could increase your energy costs.

If you want to ensure that your new clothes washer is energy efficient, purchase one with an ENERGY STAR label. Related Information

  1. Appropedia uses a reference tool that is described here. You can also click edit on this page to see the code.
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