Example of the Revised Directory of Solar Hot Water Systems

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Revised May 2005

The solar water heating systems listed were evaluated by the Florida Solar Energy Center (FSEC) in accordance with the Florida System Standards Program for Solar Thermal Systems and were found to meet the minimum standards established by FSEC. This listing also provides FSEC-developed system ratings.

Ratings have been developed by FSEC to provide the solar industry and consumers a reasonable method of comparing solar water heating systems. The ratings provided are intended for comparing solar systems and will not accurately predict the performance of a system installed at a specific site. System ratings are an estimate only and are not a guarantee. They are based on specific collector or system test results, typical operating conditions, and typical Florida climatic conditions. When multiple options are specified for a particular component, the ratings are based on the components that result in the lowest rating. The actual solar contribution can vary and is dependent on the weather, the user, and proper system installation and maintenance.

FSEC provides three annual ratings for certified solar systems. These are:

Energy Factor
Energy Output
Solar Fraction

Ratings are based on the estimated annual performance of the system as modeled using the TRNSYS system simulation program and typical meteorological year weather data (TMY2). The ratings are based on TMY2 weather data for the three regions defined by the Florida Building Code. These are North (Jacksonville), Central (Tampa), and South (Miami).

In these ratings, the quantity of hot water drawn from each solar system is equal to that of a conventional (electric or gas) water heater. The conventional water heater is defined as a 52-gallon electric water heater with an Energy Factor (EF) of 0.9, or a gas water heater with an EF of 0.6.

The performance ratings are based on the following conditions:

Table 1. Assumptions Used in Performance Calculations

Condition	Value
Hot water load	64.3 gallons (243 liters) per day drawn throughout the day with the maximum loads occurring at 8 a.m. and 8 p.m.1
Water mains temperature	Varied monthly using values for each city.2
Collector orientation	Facing south at a tilt of 24 degrees3
Distance from collector to tank	25 feet (7.6 meters) pipe length (each way), 16 feet (4.9 meters) vertical rise. Total calculation is based on 50 feet.
Backup heater set points	120ºF (48.9ºC)4
Weather conditions	TMY2 data for each city5
Air temperature around indoor tanks	Tair + [(72-Tair)/3], this estimates the temperature in a garage
1 This profile from ANSI/ASHRAE Standard 90.2-2001, "Energy Efficient Design of Low-Rise Residential Buildings", Section 8.9.4, Hourly Domestic Hot Water Fractions" and Table 8-4, "Daily Domestic Hot Water Load Profile." 2 Based on TMY2 data and the equation provided in "Building America Performance Analysis Procedures: Revision #1, Building Technologies Program, National Renewable Laboratory, NREL/TP-550-35567, Golden, CO, June 2004. pp 15-16." 3 Christensen, Craig B. (National Renewable Energy Laboratory) and Barker, Greg M., (Mountain Energy Partnership) Effects of Tilt and Azimuth on Annual Incident Solar Radiation for United States Locations, Proceedings of Solar Forum 2001: Solar Energy: The Power to Choose, April 21-25, 2001, Washington, D.C. 4 This set point was chosen to follow the International Plumbing Code 2000, International Code Council, Inc. 120ºF (48.9ºC) maximum allowable in showers and tubs. 5 TMY2 = Typical Meteorological Years, National Renewable Energy Laboratory, June 1995.

Detailed calculation methods and equations used to develop the rating methods are outlined in FSEC Standard 103-05, “Operation of the Solar Thermal Systems Certification Program.”

Energy Factors

This Directory of Certified Solar Water heating Systems provides annual Energy Factors (EF) required for use in the Florida Building Code, Chapter 13. This provides interested parties the ability to integrate solar domestic hot water heating systems into current construction or retrofit projects that require Florida Building Code, Chapter 13 compliance.

EF represents the ratio of the solar hot water energy made available by the solar system divided by the electrical energy used by the system. The annual EF is used to determine hot water credit multipliers for residential solar water heating systems in Chapter 13 of the Florida Building Code. The EF can also be used to compare the efficiency of solar water heating systems with other types of water heating systems that also use EFs as their performance rating (e.g., electric, gas, and heat pump).

The residential building performance compliance method in the Florida Building Code provides hot water credit multipliers (HWCM) for solar water heating systems based on solar system EF. The Energy Code also divides the state into three climatic zones – North, Central, and South Florida. The EF is specific for each Florida climate zone.

Just as with air conditioning and heating systems, each installation has site-specific characteristics that can affect the rated performance of the system. Recommended installation procedures must always be followed since they are equally important in determining a system's overall efficiency.

To receive Florida Building Code credits, the Energy Code requires that the solar collector(s) in a certified solar water heating system be installed as follows:

Tilted at an angle between 10 and 40 degrees of horizontal; and
Oriented to face a direction within 45 degrees of south.

These installation requirements permit a Florida solar collector to be mounted parallel to a southeast-facing to southwest-facing roof that has a pitch ranging from slightly more than 2 in 12 to a pitch as steep as 10 in 12. For installations that require that the solar collector be installed outside these practical limits, the Energy Code will not provide any water heating credit.

Energy Output Rating

The Energy Output (EO) rating is the estimated annual amount of energy (in kilowatt-hours) produced by the solar portion of the system. This represents the amount of energy that did not have to be produced by electricity of gas.

Solar Fraction Rating

The Solar Fraction (SF) rating is the percentage of the hot water load produced solely by the solar system. In simple terms, this means that if a system has a .70 solar fraction, 70% of the hot water is produced by the solar system, while the other 30% is produced by the auxiliary system.

Table 2. Example of Revised Certified Solar Thermal System Listing

System Config*	Collector		Tank		North:			Central:			South:
System Config*	Mfg	Size (ft2)	Gals	Cert Date	EF	EO (kWh)	SF	EF	EO (kWh)	SF	EF	EO (kWh)	SF
Drainback Sidearm HX	Solar Systems	40	80	July 2004	1.7	1489	0.50	2.1	1644	0.59	2.3	1555	0.62
Drainback Tank Wrap HX	Solar Systems	40	80	July 2004	2.0	1680	0.56	2.4	1761	0.64	2.5	1632	0.65
Drainback Tank Wrap HX	Solar Systems	48	80	July 2004	2.3	1845	0.62	2.8	1920	0.69	2.9	1765	0.71
Drainback Tank Wrap HX	Solar Systems	64	80	July 2004	2.6	1983	0.66	3.3	2023	0.73	3.5	1876	0.75
Indirect Tank Wrap Glycol	Solar Systems	40	80	July 2004	2.6	1979	0.66	3.4	2063	0.75	3.9	1941	0.78
Direct Diff	Solar Systems	32	52	July 2004	2.3	1830	0.61	2.9	1938	0.70	3.4	1867	0.75
Direct Diff	Solar Systems	40	80	July 2004	2.9	2102	0.70	4.2	2184	0.79	4.7	2040	0.82
Direct Diff	Solar Systems	40	80	July 2004	3.2	2169	0.73	4.9	2265	0.82	6.4	2160	0.86
Direct PV	Solar Systems	32	80	July 2004	3.4	2219	0.74	5.3	2304	0.84	6.9	2187	0.88
Direct PV	Solar Systems	40	80	July 2004	4.4	2390	0.80	8.4	2471	0.90	13.2	2335	0.93
Direct PV	Solar Systems	40	80	July 2004	4.5	2404	0.81	8.6	2408	0.90	13.8	2342	0.94
Single ICS	Solar Systems	32	40	July 2004	1.9	1584	0.53	2.2	1664	0.60	2.4	1610	0.64
Single ICS	Solar Systems	25	42	July 2004	1.7	1458	0.49	1.9	1528	0.55	2.1	1480	0.59
Double ICS	Solar Systems	64	80	July 2004	2.9	2074	0.69	3.8	2327	0.77	4.6	2030	0.81
Double ICS	Solar Systems	50	84	July 2004	2.4	1906	0.64	3.1	1979	0.72	3.6	1907	0.76

*The official listing will include system manufacturer, system model, and a detailed system type identification for consumers. The current System Configuration is being used in the rules revision process information phase as a basic identifier of the listed system types.