Emergency Shower Instantaneous Heaters

[richanton]

Based on the new 20gpm at 80 deg F requirement for emergency eyewashes, our mechanical guys have specified an instantaneous heater for each emergency eye wash. We have about 6 of them. The size of this heater is 108kw, 480 Volts. Are there any special allowances for these heaters or do I have to run a minimum 130 amp rated cable from a 150 amp breaker for each shower.

 

[mc5w]

You need to run 150 amp cable and a 150 amp circuit breaker for each heater. National Electrical Code considers any water heater that has a tank capacity of 120 gallons or less to be a continuous load. You also need enough spare feeder capacity or load shedding relays to accomodate the heaters.

Your electrical utility may also prohibit instantaneous electric heaters or limit the size to far less than what you have.

20 gallons per minute seems to be quite excessive. I have to wash my eyes every day because when my eyelashes shed they fall into my eyes. I only use 1 gallon per minute of cold water and I do not see a need to warm up the water. The wind this time of year tends to blow outdoor debris into peoples' eyes.

An much cheaper alternative would be to install 30 gallon 120 volt 1500 watt electric heaters. You can install a tempering valve to limit water temperature to 85 degrees Fahrenheit. You can also add extra insulation to reduce heat loss woithout voiding the U.L. listing but I would only do so after rewiring the heater using 180 degree Celsius nickel plated copper wire.

If you need more tank capacity a 4500 watt 240 volt heater can also be used as an 1125 watt 120 volt heater. I do not remember if the thermostat setting goes as low as 80 F but a tempering valve would provide a backup for the thermostat.

Most residential water heaters around here are natural gas, sometimes with an add-on electric heater that serves strictly as extra storage capacity.

Mike Cole, mc5w at earthlink dot net

 

[rbulsara]

I think the original poster meant emergency "Shower" or a deluge system which also contains eyewash. This is normally employed in areas with a threat of acid spills such as wet cell battery rooms.

However I agree with electrical comments made by mc5w.

 

[mc5w]

Oops, I made a mistake at 3 am in the morning. National Electrical Code rules would require a minimum of 165 amp wire and a 175 amp circuit breaker. You would need an extra 1200 amps of electrical service or equivalent load shedding to run these things. This would not come cheap and 80 gallon or 120 gallon conventional heaters would be more economical.

Perhaps you could use conventional heaters with the thermostats set at 100 Fahrenheit to supply the restrooms and then use 85 Fahrenheit tempering valves to supply the eyewashes. The heaters could then be gas, oil, electric, or steam driven.

 

[richanton]

Thanks for the info. For clarification, these emergency eyewashes are located outdoors in an industrial facility. A cost comparison was done showing that it was more economical to go this way than provide a circulating hot water loop from a tank heater located indoors.

 

[resqcapt19]

richanton,
Just for my information can you cite a source for the 80°F requirement? I work at a plant with outside safety showers and the water is not heated, other than to provide freeze protection for the supply piping and the shower. Thanks.
Don

 

[richanton]

The requiremetns for the eyewash and shower are from ANSI Z358-2004. The requirement is recent and does not require retrofit of existing installations as far as I know.

 

[mc5w]

I wonder who thought that instaneous electric heaters would be more economical than a hot water recirculation pump? 1200 amps of wiring, load shedding relays, and so forth is NOT cheap. A hot water recirculation pump for this application is by far cheaper to wire and decent pipe insulation minimizes thermal losses to very low levels.

Something has to be wrong with the cost calculation. An instantaneous heater that directly mixes medium pressure steam with cole water is very economical for this application because the boiler and piping provide energy storage. Electric instantaneous have to be about the most expensive method I could imagine.

Mike Cole

 

[richanton]

The cost calculation was based on the fact that the heater was located about 150 feet away. The piping would have to be heat traced. Recirculation pumps wouls have to run continuously to maintain the temperature in the whole loop.
However, I agree with you. I inputted the cost numbers for electrical, but I think the mechanical engineer who did his cost analysis did something wrong.

 

[advidana]

yes he did something wrong