Green/Eco Remodeling and Construction, Custom Homes - St Louis Missouri

The average annual operating cost for a standard hot water heater is $500 or higher.  This is for a 50 gallon water heater with a life expectancy of 8 to 12 years.  A solar hot water heater, on the other hand requires an annual operating cost of only $50, has a capacity of 80-120 gallons and has a life expectancy of 15 to 30 years (SolarDirect.com). 

The payback for a solar hot water system is approximately 7 years.  This is due in part to the tax credit that is available from the government.  This tax credit is for 30% of the system cost and eligibility has been extended to the year 2016.  The system cost in a new home or existing is approximately the same.  The cost for an 80 gallon tank using 1 to 2 solar panels is approximately $5400 and the cost for a 120 gallon tank using 2 to 3 panels is approximately $7000(MissouriSolarLiving.com).  

Another payback from solar hot water heat is the environmental benefit.  The use of solar power reduces the use of fossil fuels for heating purposes.  Carbon dioxide emissions can be reduced by approximately 2000 lbs per year for each solar hot water heater.  Nitrous oxide emissions can be reduced by approximately 1 lb per year for each solar hot water heater. 

Theory of Solar Heating and Terms

Solar Constant - The rate of solar energy hitting the earth’s atmosphere assuming no loss is 429.2 BTU’s per hour per square foot.  This energy if collected for three hours without any inefficiency could power the entire earth for one year. 

Insolation - Since the earth’s atmosphere filters out much of the sun’s energy, the most efficient we can be inside the atmosphere is about 70% or 320 BTU’s per hour per square foot. 

Wavelength Conversion - Solar radiation is a stream of short wavelengths that becomes thermal energy when it is absorbed.  The thermal energy is composed of a new stream that is wavelengths that are 10 times longer. 

Greenhouse Effect - Many materials like the atmosphere will allow the passage of the shorter wavelengths of light but will not allow the returning longer wavelengths of heat to exit.  This “Greenhouse effect” is used in many solar collectors to maximize thermal energy.  

Black Body - Materials that are good at absorbing radiant energy and re-radiating that energy are called black bodies.  The most efficient black bodies can re-radiate up to 96% of the energy that arrives. 

Absorber - An absorber is that portion of the solar collector that contains the black body.  It is usually a flat black surface with a high absorbance rate.  It is responsible for converting the radiant energy into heat. 

Flat Plate Collector - This is the most efficient type of collector in areas where the temperature can get below freezing.  It is made of an absorber, heat exchanger and also includes insulation, glazing, plumbing and the casing to enclose the entire assembly.  These collectors are usually set up facing to the South and tilted at an angle to catch the most amount of radiant energy.  The other advantage to Flat Plate Collectors is that they can absorb diffuse radiation that is produced on cloudy days. 

Convection - This is the basic form of heat transfer that occurs in a solar collector.  A cool liquid or gas is heated in the collector and then moves away to be replaced by more cool material.  This simple process allows for the continual heating of water during times when radiant energy is available (SolarExpert.com/Heat-theory). 

Basic System Operation

The solar hot water system can be either a one-tank or two-tank system.   

A One-tank system has one tank that is heated from the solar system as well as the conventional heating system. 

Two-tank systems have one tank that only heats water using the solar heat system.  This water is then transferred into a second tank that can be heated using a conventional heater if needed.

In an existing home scenario, there is a cost saving option that is available.  In certain circumstances, the existing water heater can be integrated into the solar hot water system.  The cost savings in utilizing the existing hot water heater can be as high as $800.  There are a few basic requirements that are necessary:

Existing electric hot water heaters can be utilized in a one tank system to work with a solar hot water system if thery are less than 5 years old and are at least 80 gallons.  The reason not to use electric hot water heaters older than 5 years is because they will have deposits in the bottom of them that can cause problems in the functioning of the solar hot water system.  If they are smaller than 80 gallons, they do not have enough capacity to be retrofitted to include the solar system.  With the electric hot water heater, the tank will be retrofitted to act as the storage tank and the back up heat source in one. 

Existing gas hot water heaters can be used as the back up in a two-tank solar hot water system.  A separate solar storage tank is installed and then feeds in to the cold water supply of the gas back up heater.  The back up heater will only ignite if the heated water from the solar tank cannot keep up with demand.  The problem with the two-tank system is that it requires additional space that some people may not have in their basements.  The gas hot water heater can be an older heater and can be as little as 50 gallons since it is only being used as the backup.

In warm climates, the cold water is transferred to the roof using a pump and lines to the solar collectors on the roof.  The water is heated and then is returned to the storage tank.  The water from this solar tank is now the supply water that goes into the conventional water heater portion of the system.   

In colder climates, a non-freezing transfer fluid is pumped to the roof and passes through the solar collectors.  It returns to the water heater and then gives off heat through a heat exchanger inside the water heater (EnergySavers.gov).   

The conventional portion of both systems will only ignite if the solar portion cannot keep up with the demand for hot water.  Most solar systems will provide 70% of the required hot water.  The burner element in the conventional portion of the heater will take care of heating the other 30% of the water (SolarExpert.com). 

Conclusion

Heating and Cooling are two of the highest energy use processes in a home.  53% of the energy use in the home is for heating and cooling (Energy Kids).  There are many ways to reduce that energy cost.  These can include better insulation, more efficient windows, thermostat temperature settings, home design and higher efficiency equipment.   The discussion for this article is going to focus on one of the most efficient ways to heat and cool your home.  This involves Geo-Thermal Ground Source heat pumps.

 There is one large advantage with Geo-Thermal Ground Source Heating Pumps.  The source for heating and cooling is derived from the ground temperature rather than the air.  The temperature of the ground varies by location but in the Midwest, it stays around 50 to 55 degrees (GreenCast).  Air source Heat Pumps must use Air temperature for their heating and cooling.  As you are well aware, air temperature varies widely during the year.  In the summer it may reach above 100 degree temperatures and the winter it may dip below 0 degrees.

The main question is why is the ground temperature more efficient for the cooling and heating of your home?  The best place to start with this answer is to explain how a heat pump works. 

A heat pump has the ability to switch directions by opening and closing valves.  This allows it to cool in the summer and heat in the winter.  A heat pump actually removes heat from the air.  In the heating cycle, it is doing the reverse of air conditioning.  It extracts heat from the outside air and sends it to the inside.  In the cooling cycle, it takes the heat from the air inside the home and sends it to the outside.  To perform this function, it uses a refrigerant that is constantly expanding and contracting. 

In the heat cycle, the cycle starts with the refrigerant in the heat pump passing through the heat exchanger and absorbs heat from the outside air.  The refrigerant evaporates as it is heated into a gas.  The gas refrigerant is put through a compressor and is pressurized until its temperature is over 180 degrees.  The hot gas passes through a refrigerant to air heat exchanger where the heat is extracted and sent through the heat ducts.  The refrigerant changes to a liquid as it loses heat and then cools as it passes through an expansion valve to start over. (Ground Loop). 

In the cooling cycle, the process is reversed.  The refrigerant is leaving the house as a warm gas.  It is compressed and gives off more heat outside the house.  The fan in the pump cools the heat coming off of the compressor as it compresses the refrigerant into a cool liquid and sends it into the house.  It passes through an expansion device and cools rapidly before entering the condenser.  The hot air from the house is blown across it.  The air cools as it passes over the condenser.  The heat is drawn from the inside air and begins to heat the refrigerant as it exits the house as a gas.  The cycle begins again.

Now that we understand how the heat pump works, let's discuss the in-efficiencies of the Air Source system.  In the winter, the heat pump is extracting heat from the outside air to aid in heating the refrigerant and changing it into a gas.  The colder that the outside air is, the less heat is available to aid with this process.  In the summer, the heat pump is trying to release heat from the compressor and cool the refrigerant to condense it into a liquid.  In the summer, however, the outside air temperature can be extremely high which forces the heat pump to work much harder to extract the heat from the system.  Even though a heat pump is a more efficient system than a standard split system, it still has several efficiency hurdles to overcome as it does its job.

This brings us to the Ground Source Heat Pump solution to the problem.  The ground source system circulates a liquid through the ground so that it takes on the temperature of the soil. This temperature is a fairly constant 50 to 55 degrees for the Midwest.  This liquid is used to perform the same work as the air in the Air Source system.  In the winter the heat pump is extracting heat from 55 degree liquid instead of battling with much colder air.  This warmer liquid will be much more effective in changing the refrigerant into a gas in the winter and producing the heat cycle.  In the summer the liquid from the Ground Source is much more effective in cooling the refrigerant in the system than the hot outside air. 

Now that we understand the efficiency of the Ground Source liquid cooling, let's discuss how it gets to the heat pump.

There are 3 basic types of closed loop systems.  They are as follows:

• Horizontal Loop systems are used in areas where land is plentiful and soil may be shallow.  The system of pipes is placed in trenches that are 4 to 6 feet deep.  1 to 6 pipes may be placed in each trench.  Trenches can be 100 to 400 feet system ton.  The trenches are placed 6 to 10 feet apart.  The overall land area required can range from 750 to 1500 square feet per system ton.
• Vertical Loop system is used when land area is scarce.  Drilling equipment is used to bore small diameter vertical wells.  The pipes are lowered into each well to produce a U-shape at the bottom and form a continuous flow down and up.  Hole depth can vary from 100 to 300 feet per system ton.  The holes are separated 10 to 15 feet.  The land area required per ton is only 100 to 200 square feet.
• Lake Loop systems are very economical when bodies of water are readily available.   The coils of pipe are laid on the bottom of the lake and in most cases, ¼ to ½ acre of water surface at a depth of 8 to 10 feet will accommodate a typical residence.

Installation of the loop system is one of the most expensive parts of the Ground Source system. In either the Horizontal or Vertical loop system, excavation or drilling equipment is needed. Each well in the vertical system can cost as much as $2500.  One well is installed for each ton of cooling.  This expense plus the increased cost of the Ground Source equipment can cause the cost of a Geo-Thermal system to be 30% to 100% times the cost of a high efficiency system.  A great source for cost comparisons is a website called (HVAC- Op Cost).  This site allows you to input the efficiency of the system that you are contemplating and to see the cost return on the system.  You may need someone familiar with the mechanical systems to help you with all of the numbers to input.

If the cost of a Geo-Thermal system is that expensive, will it pay to install?  The payback is largely dependent on the climate and the demands of heating and cooling.  The payback can be as quick as 5 years and can extend to 7 or 8 years (EcoHome). 

So Geo-Thermal is not for the faint of heart.  It takes a commitment for the long haul.  If you are willing to make the investment, you will have a system that runs quietly and efficiently for many years and will certainly increase its value as energy costs continue to rise.

Much of the information for this article was supplied by my local Heating and Cooling subcontractor.  (Vogel Heating & Cooling) has been installing quality mechanical systems in the St. Louis area for over 60 years.  They are a (Carrier) dealer and have always provided me with quality equipment at a fair price.