Issue: DCA10-DEC-034.  C.W. “Ben” Bentley of the LeverEdge company, Pasco County, Petitioner, is requesting clarification regarding Section M2301.2.3 of the Florida Building Code, Residential.

 

Petition asks the question, “Is it the intent of 2007 Florida Building Code [Residential] to allow installation of a PRV [pressure relief valve] valve in the “solar loop” portion of an active direct solar water heating system?”

 

Background:

 

1.      Petitioner is a manufacturer and distributor of approved FSEC solar water heating systems, #1175, model #0-80-40. Petitioner provides complete packaged systems to multiple dealers for installation in Pinellas County.

2.      In the case specified, a dealer returns the system PRV valve and asks for P&T valve replacement which, when replaced, causes premature system failure resulting in a bad reputation for the entire solar industry. Petitioner has sold complete fabricated solar domestic residential water heating systems to certified solar contractors since 1979, including the proper pressure and temperature relief valves. The system includes a P&T valve, to be installed on the water heater/solar storage tank combination, and a pressure relief valve to be installed on the isolatable side of the “solar loop”.

3.      Florida Building Code, Residential

M1302.1 Listed and labeled. Appliances regulated by this code shall be listed and labeled for the application in which they are installed and used, unless otherwise approved in accordance with Section 104.11 of the Florida Building Code, Building.

M1307.1 General. Installation of appliances shall conform to the conditions of their listing and label and the manufacturer's installation instructions. The manufacturer's operating and installation instructions shall remain attached to the appliance.

M2301.2.3 Pressure and temperature relief.  System components containing fluids shall be protected with pressure- and temperature-relief valves. Relief devices shall be installed in sections of the system so that a section cannot be valved off or isolated from a relief device.

4.      Florida Building Code, Mechanical:

Section 202.  PRESSURE RELIEF VALVE. A pressure-actuated valve held closed by a spring or other means and designed to relieve pressure automatically in excess of the device’s setting.

Section 1402.5.1 Pressure and temperature. Solar energy system components containing pressurized fluids shall be protected against pressures and temperatures exceeding design limitations with a pressure and temperature relief valve. Each section of the system in which excessive pressures are capable of developing shall have a relief device located so that a section cannot be valved off or otherwise isolated from a relief device. Relief valves shall comply with the requirements of Section 1006.4 and discharge in accordance with Section 1006.6.

5.      Petitioner states: Installing a P&T valve on the isolation side of the loop causes premature system failure which decreases petitioner’s potential for future sales. It is a fact and the petitioner’s contention that solar collector temperature can not be regulated by a valve when the collector is isolated. Since the collector temperature, under a stagnant and isolated condition, far exceeds the temperature setting on any hydronic T&P valve, the thermal gel inside the temperature probe is compromised, allowing even tepid water to discharge from the system, rendering the system inoperable. On the other hand, a pressure relief valve, when the loop is isolated and the pressure producing fixture (the collector) heats up, thermal expansion creates pressure, opens the PRV and spills a cup or so of water onto the roof, closes and repeats as necessary to provide safety from over pressurization but not temperature since the collector temperature will continue to increase until it reaches it’s maximum potential for that particular sun condition. Therefore, a pressure relief valve is the valve of choice for manufactures and installing contractors for “solar loop” protection since the PRV provides safety protection and is relatively service free. See attached FSEC “Solar Thermal Manual” support sheets and FSEC system approval sheet, system #1175 for system model #0- 80-40 with isometric drawing showing PRV valve installation location.

6.      The Florida Building Code 2004 Commentary, Vol. I, Residential, describes Section M2301.2.3 [unchanged since the 2004 code] as follows:  “Pressure and temperature relief valves are important to prevent pipes bursting because of high collector temperatures. Flat plate collectors used for domestic water systems are designed with glass coverings and an insulated housing to increase the efficiency of the collection system. The collection surface, or absorber plate, can easily heat up to 200oF (93oC) on a freezing winter day and up to 400oF (204oC) on a summer day when the water is stagnant and not circulated through the collector. These valves are often installed as part of the collector system. These valves must also be installed on the storage tank and back-up water heater.”

7.      It is the petitioner’s contention that M2301.2.3 says that more than one type of relief device can be installed. Otherwise, instead of saying what it says above, “System components containing fluids shall be protected with pressure- and temperature-relief valves. Relief devices shall be installed in sections of the system so that a section cannot be valved off or isolated from a relief device”, it would have said, “System components containing fluids shall be protected with a pressure and temperature relief valve. A P&T valve shall be installed in sections of the system so that a section cannot be valved off or isolated from the P&T valve”.

8.      The International Mechanical Code Commentary, 2003, clarifies Section 1402.5.1 as follows:  “Any heated, closed system is capable of developing pressures that exceed its design working pressure. Closed liquid-filled systems can develop high hydrostatic pressures with even slight temperature increases. Because solar energy varies in intensity, the collector system is subject to greater temperature and pressure variations than other heating systems having precisely controlled energy inputs. Additionally, the solar energy input cannot be turned off by limit controls as can other energy sources. Therefore, a solar energy system is more likely to be subjected to extreme temperatures and pressures that could cause system failures and the associated hazards. Pressure and temperature relief valves are necessary to prevent injury and property damage that could result from the failure of pressurized vessels and piping. Typical liquid solar energy system involve large complex piping circuits with valve arrangements that greatly increase the likelihood of portions of the piping system being isolated from the overpressure or over temperature safety devices . Any portion of a system isolated from the relief valve or valves is unprotected from the danger of excessive pressures and temperatures. To ensure complete protection to all portions of a system, multiple relief valves at different locations in the system may be necessary.

9.      Florida Building Code, Building:

102.1 General. Where, in any specific case, different sections of this code specify different materials, methods of construction or other requirements, the most restrictive shall govern. Where there is a conflict between a general requirement and a specific requirement, the specific requirement shall be applicable.

 

Staff analysis: 

·         The solar system in question holds an FSEC certification “#1175, model #0-80-40 and as part of the certification, a “Solar Thermal Manual” and isometric drawing showing valves installation location are provided.  According to FSEC staff, a certified residential solar system will normally have two valves:  One valve “pressure and temperature “P&T” relief valve” to be installed on the water tank and the second valve “pressure relief valve” to be installed on the isolatable side of the ‘solar loop’.  Further, according to FSEC staff and from experience, it has been noted that installation of a P&T valve on the isolation side of the loop will cause the valve to open frequently, causing the valve to malfunction due to the frequent use.    

·         Section M2301.2.3 requires that system components containing fluids must be protected with pressure – and temperature relief valves.  This section is general and does not provide specific details for location, installation and distribution of the relief devices within a specific residential solar system.

·         Section M1307.1 requires that installation of appliances must conform to the conditions of their listing and label and the manufacturer’s installation instruction.

·         According to Section 102.1, it is the staff opinion that the provisions of Section M1307.1 are more specific with regard to placement and distribution of relief valves for the system in question than that of Section M2301.2.3.  Therefore, the use of a P&T or PRV must be as per the system’s listing and the manufacturer’s installation instruction.

 

Recommendation:  Based on the background information described above, staff makes the following recommendation:

 

To the question “Is it the intent of 2007 Florida Building Code [Residential] to allow installation of a PRV [pressure relief] valve in the “solar loop” portion of an active direct solar water heating system?”, the answer is YES, as long as the installation is in accordance with the system’s listing/certification and the manufacturer’s installation instruction.