Water Heating Systems for Laundromats - part 1.
Customers come into your Laundromat and they RENT your washers and dryers. But what are they really purchasing? Hot & Cold water. I am going to discuss my opinions on Water Heating systems for Laundromats. There are currently 2 different types of hot water heating systems used in Laundromats; water heaters with "storage tanks" and heaters without storage tanks also known as "instantaneous" or "tank-less" heating systems.
Storage Tank Water Heaters
As the name implies a "Storage Tank Heating System" uses a storage tank to hold hot water and has enough Hot water in storage to handle many washing machines operating at once. When a customer starts 6 large washers there could be an instantaneous demand for up to 100 gallons of Hot Water. The storage tank system has an insulated storage tank that holds 120-130 degree Hot Water. In addition to the storage tank there is a high recovery water heater and circulator in a loop to keep the storage tank at the desired temperature. As hot water is used, cold water enters the storage tank and once the tank temperature hits the low temperature reset point, the circulator and heater turn on and high capacity heater heats the water back up to the desired (125 deg.) temperature. This system works quite well and always has a Hot water in storage for the Laundromat customers. The downside is that you are always maintaining Hot water and using energy even when the store is closed or running at minimal operations.
Instantaneous Water Heaters
The "instantaneous water heater" is one big heating coil sitting over a large flame. The flame only turns on when there is a demand for hot water. Since there is No storage tank, all of the hot water is produces only when needed. The heater is a sealed unit and the water flow rate is restricted so that the water leaving the heater is already at the desired Hot water temperature. Physics says that an "instantaneous heater" can only produce a certain amount of Hot water, at a certain flow rate (see attached chart). Typically the instantaneous heater will produce 9-10 GPM (gallons per minute) of flow rate for a 30 degree rise in temperature. The difference between the desired Hot water temperature (typically 125 degrees) and the temperature of the incoming cold water, is called the "# of Degree (of) Rise" in temperature. For example in the NY area incoming water temperature in the winter can be as cold as 40 degrees (see attached chart for your area). If our desired Hot Water temperature is 125 degrees then we need an 85 degree rise in temperature. The water heater with an 85 degree temperature rise will only have a flow rate of 4 GPM. Note that the typical front load washer fills at between 5-7 GPM. With an "instantaneous water heater" the higher the degree rise, the lower the hot water flow rate. Multiple "instantaneous water heaters" are required to produce enough Hot water (flow rate) to satisfy the demands of even a modest Laundromat. If the hot water heating system is designed correctly then both heating systems will operate properly and the Laundromat customers will have plenty of Hot water. If the water heating system is sized wrong or under-sized, then the Laundromat will experience noticeable problems.
Ordering the System
In a situation where the water heaters are undersized, the Laundromat washers will suffer and the lack of hot water will become apparent to your Laundromat customers. Laundromats are busiest during Saturday and Sunday usually between 8am to 6pm. If the "storage tank heating system" is under-sized the temperature in the storage tank will Not reach the desired temperature. The heater will be operating almost continuously, trying to make enough hot water (which shortens the heater life) and the customers will be getting cooler and cooler "Hot" water.
With an "Instantaneous water heater" if there is too much hot water demand the heaters will only produce 4 GPM of hot water per heater (with an 85 deg rise) and the Hot water flow rate will diminish. If the hot water demand exceeds the capacity the heaters, the result will be very little Hot water flowing to the washers and the washer cycle times will increase. For example, imagine turning on every water faucet in your house, the flow rate to each faucet will drop as more and more faucets are turned on. This is what happens in your Laundromat. As more washers call for Hot water, the flow rate will decrease with each washer and the water will trickle into the machines. Some Laundromat owners will install 2 "instantaneous heaters" when 3 or 4 should have been installed. In 90% of the time this is not a problem, but for the busiest 10% of the times, the Laundromat washers will start filling slower and the washer cycle times will increase from 30 to possibly 45 minute per cycle.
Next week we will discuss how to size your water heating system.
Incoming Water Temperature Chart
Tankless Heater Flowrate vs. Degree Rise
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