Healthcare Facility Plumbing Design, Part 2
By Ron George, CPD
President, Plumb-Tech Design & Consulting Services LLC
Plumbing commissioning
Plumbing systems should be integrated into the commissioning plan. The plumbing commissioning plan should include commissioning procedures for the following systems and equipment:
1. Pressure test procedures for all pipe systems
2. Shower or bathroom basin leakage tests
3. Plumbing fixture carrier installation
4. Plumbing fixture flow rate adjustment
5. System chlorination and flush.
6. Booster pump package start-up procedures and pressure settings. Verify the installation is installed in accordance with the manufacturer’s instructions.
7. Domestic hot water systems temperature requirements verify HW temperature in water heater is at a temperature above 135 F and HWR balancing valves are set for a 10 degree temperature difference.
8. Domestic hot water heater temperature settings. Verify the installation is installed in accordance with the manufacturer’s instructions and the outlet temperature is in accordance with the system design.
9. Domestic hot water circulating pumps and balance valve settings to maintain HW temperature at design conditions.
10. Verify that the maximum temperature limit-stop on the shower valves is set to the temperature specified to prevent scalding.
11. Thermostatic mixing valve temperature settings under flow. Verify the installation is installed in accordance with the manufacturer’s instructions and verify that the outlet temperature is in accordance with the system design.
12. Vacuum system, test of alternation of pumps and test of all alarms, set vacuum switch settings. Verify the installation is in accordance with the manufacturer’s instructions.
13. Medical air system, test of alternation of compressors and test of all alarms, set pressure switch settings. Verify the installation is in accordance with the manufacturer’s instructions.
14. Laboratory air system, test of alternation of compressors if duplex units and test of all alarms, set pressure switch settings. Verify the installation is in accordance with the manufacturer’s instructions.
15. Compressed gas manifold systems, test the changeover valve for each system and test all alarms on the gas system. Verify the installation is in accordance with the manufacturer’s instructions.
16. Oral evacuation system, test of alternation of pumps if duplex units and test of all alarms, set vacuum switch settings. Verify the installation is in accordance with the manufacturer’s instructions.
17. Dental compressed air system, test of alternation of compressors if duplex units and test of all alarms, set pressure switch settings. Verify the installation is in accordance with the manufacturer’s instructions.
18. Natural gas and fuel system, verify gas pressures at static and under load conditions to assure proper gas pressure for proper flame at the burner.
19. Pure water systems, verify system flushing and test the water quality to determine if the water quality is within specifications. Verify the installation is in accordance with the manufacturer’s instructions.
20. Perchloric acid hood automatic wash down system, Verify the hood exhaust fan is performing per the specifications, verify water and drain connections allow proper washdown per the manufacturers instructions.
21. Kitchen hood automatic wash down system, Verify the hood exhaust fan is performing per the specifications, verify water and drain connections allow proper washdown per the manufacturers instructions. Verify drain is routed to the grease waste system.
Water distribution systems
Size the piping for the hot and cold water systems not to exceed the maximum velocity allowed by the Copper development association for copper piping. For cold water piping the maximum velocity should be 8 feet per second and for hot water piping systems the maximum velocity should be five feet per second.
Minimum pressure
Maintain a minimum pressure of 35 psi at the highest plumbing fixtures. In minimum pressure calculations, use residual pressure at design flow. Monitor for diurnal pressure fluctuations experienced by the building water supply and modify starting pressures accordingly. Provide a pressure gauge on the top floor branch adjacent to the riser.
Water hammer arrestors
Provide necessary water hammer arrestors that are certified to meet the requirements of the American Society of Sanitary Engineers Standard 1010, Water Hammer Arrestors. The sizing and location of the water hammer arrestors should be per the Plumbing and Drainage Institute (PDI) Standard PDI-WH 201, Water Hammer Arrestors, latest edition, requirements. Show quantity and type of water hammer arrestors on plans and riser diagrams. Water hammer arrestors should be located near any quick closing valve and installed with inlet isolation valves to allow for removal and servicing.
Trap primers
All floor drains and floor sinks should have a single or manifold electronic trap primer supply. The trap primer control box should be recessed. Traps located 50 ft from the control box should be piped to that control box unless shown otherwise on the construction documents.
Wall hydrants
Provide wall hydrants a maximum of 200 ft apart at loading docks and at building entrances, with a minimum of one wall hydrant on each exterior wall.
Backflow preventers
All lab sinks with hose connections should have vacuum breakers. All hose valve connections should have hose type vacuum breakers. All laboratory and process water systems should have a reduced pressure backflow prevention device installed on the branch serving those systems. There should be a reduced pressure backflow prevention device on the water supply to all pure water systems, reverse osmosis, hemodialysis, and reagent water distribution systems.
Minimize the use of pressure-reducing valves – pressure zones
Minimize the use of pressure-reducing valves by providing separate pressure zone with separate pumps for each pressure zone and separate domestic hot water heating systems for each pressure zone.
Hot water branch lines
Provide a means to “heat and flush” the domestic hot water branch lines by providing a 1/2-inch drain and shut off valve extended to a floor sink.
Domestic water booster pumping system
Designers should consider at least a three-pump booster system for a hospital and they should use a four-pump booster system to allow for smaller pump sizes and greater energy savings.
Three-pump systems can be sized with one pump at approximately one-third or 34 percent of the total water demand the other two pumps at two-thirds or 66 percent of the demand. With this sizing, any one of the pumps can be out of service and the system can still meet 100 percent of the demand. Another option for a three-pump system is for each pump to be equally sized at 50 percent of the load. Again any one pump can be out of service and the system can still meet the demand.
Four-pump systems can be sized with two pumps at approximately one-quarter or 25 percent of the total water demand the other two pumps at one-half or 50 percent of the demand. With this sizing, any one of the pumps can be out of service and the system can still meet 100 percent of the demand. Another option for a four-pump system is for each pump to be equally sized at 34 percent of the load. Again any one pump can be out of service and the system can still meet the demand. The four-pump system allows a smaller pump to run for the majority of time when there is little demand. This equates to less horsepower consumption and energy savings.
For pump sequencing of the multiple pump systems, each of the smaller pumps should alternate and operate until water demand exceeds the smaller or lead pump‘s capacity, at which point that pump should stop and one of the other larger pumps should start.
When the demand exceeds the capacity of the larger pump, the smaller pump should restart and both pumps should operate together. When the demand exceeds both the large and small pumps’ capacities, both of the larger pumps should come on. The other large pump should be a standby and alternate with the first large pump. The system should be capable of operating at full capacity with one pump out of operation.
The plumbing designer should provide a hydro-pneumatic tank connected to the cold water system downstream of the booster pump to allow the booster pump to shut down during periods of low or no flow for energy savings. The designer should coordinate with the electrical engineer to make sure the booster pump is connected to the emergency power supply system. The discharge pressure can be controlled by a pressure reducing valve or it can be controlled using variable frequency drives through the packaged booster pump controller. The booster pump package should be specified with spring-loaded swing check valves to reduce water hammer when the pumps shut down.
Domestic hot water systems
Patients in healthcare buildings often have suppressed or weakened immune systems. A healthy adult exposed to a moderate amount of Legionella bacteria might experience a few slight flu symptoms while the body’s immune system fights off the invading Legionella bacteria. The problem comes when the immune system is weakened and cannot put up a good fight against Legionella bacteria. Legionella bacteria is transmitted to people when they breathe in water vapor or ingest water with Legionella and choke or inhale water with a the bacteria. Shower heads, indoor fountains, cooling towers and any source of water mist provides a path for the bacteria to ride a microscopic water droplet into someone’s lungs. Once the Legionella bacteria makes it to the warm moist lungs, the lungs provide a perfect breeding ground at an ideal temperature for incubating the bacteria. This is why designing plumbing systems and specifically domestic hot water systems to minimize Legionella bacteria growth is so important.
Hot water system temperature controls
No building, especially a hospital, should rely of the thermostat on a water heater for controlling the hot water temperature delivered from the fixtures in a building. The model plumbing codes specifically prohibit the water heater thermostat from being the final temperature control for hot water delivered from the fixtures. This is because the thermostat on most water heaters is located near the bottom or inlet connection of the water heater and the water heater thermostat is designed to anticipate cold water coming into the heater in order to turn “on” or “off” the heating element. The water heater thermostat is generally not designed to accurately control the outlet temperature of the water heater. It is common for most water heaters to experience temperature swings of variations. Some temperature swings can be as much as 30 degrees Fahrenheit at the outlet of a water heater. A master thermostatic mixing valve conforming to ASSE 1017 should be used near the outlet of a water heater to mix hot water with cold water and deliver a relatively constant temperature of hot water to the hot water distribution system. Other hot water system temperature controls can be used to control the hot water distribution temperatures to the maximum recommended temperature for the application or at the fixture by using local mixing valves or temperature limiting valves conforming to ASSE 1070, and/or Point-of-use mixing valves conforming to ASSE 1016. These devices should be used to reduce the hot water distribution temperatures to the maximum recommended temperature for the application. The maximum delivery temperature for showering, bathing and hand washing fixtures should be 120 degrees Fahrenheit or the temperature required by the local codes. Sitz baths, bidets, hydrotherapy baths and whirlpool baths typically require maximum temperatures less than 110 degrees Fahrenheit. Check the local health department and the local code for the maximum temperature for these fixtures.
Water heaters
Generally, water heaters in a hospital are storage type or semi instantaneous type water heaters with storage temperatures kept above 135 to 145 degrees Fahrenheit to minimize Legionella bacteria growth. When storage temperatures are high enough to kill Legionella bacteria, a mixing valve should be used to reduce the hot water to a safe temperature.
Water heaters can be storage type, instantaneous type or a combination of a small storage tank with an instantaneous heater, generally referred to a semi-instantaneous type. Fuel sources for water heaters can be steam, heating hot water, electric, fuel gas, fuel oil or a combination of fuels in duel fuel burners.
Instantaneous type heaters are sometimes used but generally do not perform as well as semi-instantaneous or storage type heaters when there are large variations in flows. Instantaneous water heaters generally are not designed to raise the system temperature high enough for disinfection temperatures. Instantaneous heaters generally only raise the hot water temperature to the usage temperature and not disinfection temperatures. Many instantaneous heater designs are also prone to temperature swings due to the location of the temperature sensor in relationship to the steam or heating hot water control valve and the inherent delay associated with the thermostatic element and the valve actuation process reaction times. Many instantaneous heaters also have significant pressure drops and can experience high velocity erosion and temperature drops during peak flow rates.
Water heaters are generally centrally located in one or more equipment rooms at or below grade. In high rise buildings the water heater should be in the same pressure zone as the cold water piping so as not to cause recirculation pressure problems or pressure relief valve problems. Pressure reducing valves and re-pressurization pumps should be avoided in domestic hot water systems. Pressure reducing valves and re-pressurization pumps generally are a sign of a poor system design and they increase the energy costs and maintenance costs of the building because they do not to last very long in hot water environments. This usually leads to pressure and circulation problems that in some cases have led to scald incidents.
The designer should determine whether the domestic hot water heat source will be steam, fuel oil, electric or natural gas. The designer should also determine if there will be any solar or heat recovery, heat exchangers used for pre-heating domestic hot water. This information will aid in selecting the appropriate water heating equipment.
Hospitals generally have a requirement for steam for building heating, humidification, kitchen equipment or for sterilizers. When steam is available, consider providing duplex, double wall steam to hot water shell and tube water heaters with a moderate storage capacity to serve as a buffer tank for temperature fluctuations. The heaters should have the capacity to generate the peak flow demand at 160 degrees Fahrenheit for sanitation temperatures with each water heater sized to supply 100% of the demand. The heater storage temperature should be set at about 135 to 145 degrees Fahrenheit. A high temperature alarm should be installed on the hot water main leaving the Master Thermostatic mixing valve and the alarm should be wired to the building management system.
Shower valves
Shower valves should meet the requirements of: ASSE 1016 Performance Requirements for Automatic Compensating Valves for Individual Showers and Tub/Shower Combinations. These valves have a maximum temperature limit stops that must be field adjusted when the hot water system is operational to limit the supply of hot water to a maximum of 105 degrees Fahrenheit at the shower head. The shower valves should be of the combination temperature and pressure (TP) compensating type shower valves. The domestic hot water system should have a re-circulating system to maintain hot water at remote areas of the building. Flow balancing valves, check valves and isolation valves should be at the end of every hot water main with the balancing valve adjusted to provide a temperature drop in accordance with the sizing guidelines in the domestic hot water systems chapter of the American Society of Plumbing Engineers, “Plumbing Engineering Design Handbook” or as described in the “Service Water Heating Systems” chapter of the “2011 ASHRAE Applications Handbook.”