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Building Principles: Some Like It Hot!
Sometimes we have an opportunity to grow a bit beyond our comfort zones. We thought that what we learned in the course of mapping out a solution for our client on this project might just help some of Camping Magazine's readers. Heating water for showers or kitchen use has historically been done in one of two ways. Either a "commercial" hot water heater or a boiler raises the temperature of a certain amount of water, and an insulated tank holds that heated water until someone opens a tap. A thermostat would periodically turn the heating cycle on when the stored water temperature dropped beyond a certain point, and then turn the heater off. This would repeat indefinitely regardless of whether anyone was in camp or not.
When energy (in the form of LP or natural gas, heating oil, or electricity) was (relatively) cheap, this cycling was considered an unavoidable cost of doing business, and the bill for the fuel or electricity was dumped into "overhead costs." Other parts of this scheme were also lumped into "the way things are" category including the danger with over-pressurized storage tanks, draining them completely for the winter and filling them in the spring.
Hot Water at Camp
One day this spring during a site visit, we found our client's hard working site caretaker (we'll call him "Ed,") struggling with a repair on a maze of pipes and pumps arranged to heat and recirculate enough hot water to satisfy the needs of the kitchen for cooking and dishwashing. The cinder block building where these components were housed was cramped and poorly lit. It seemed to be speaking to me, but it turned out to be Ed talking to the equipment. "Hey, Ed! What's up?" was all it took to get him to reel off a pretty descriptive litany about his experience with this critical link at camp. "The health department has a fit every year because the water isn't hot enough. So we turn the boiler up. Then the water's a scald hazard, and the pressure goes out of sight in the storage tanks," which, it turns out wasn't pressure rated for this application. "Soldered fittings blow out, and pipes crack," he continued. "The parts were assembled piecemeal over the years, the drains are all hard to get to, and the building floor doesn't have a drain to get rid of the water when we winterize. Most important though is safety."
When something blew, he had to turn off the LP and allow the scalding hot water pressure to abate before he entered the shed. The lament was heartfelt. He had asked for a new system, and the local plumber had proposed to install new hot water heaters. But he wasn't completely certain that a new hot water heater would address all of the operational, maintenance, and management issues.
Searching for the Right Water Treatment System
Given what I could see, I was inclined to agree with him. There had to be another way to "defur this feline," which would be safe(r), simple(r), more reliable, and less expensive to operate and maintain. With the director's approval, we looked into the issue using our experience in water treatment plant design as a basis for the search. Most large municipal treatment plants have testing labs on site. On several projects, we had specified and installed "tankless" hot water heaters. These compact units store no hot water at all, but instead heat water only on demand (when someone opens a faucet). The big question in my mind at the time was whether we could find a unit that would meet the flow rate, volume, and temperature requirements since the units we had specified were only for small amounts of water for sink use (low flows and temperatures less than 130°F).
To begin, we needed some basic information. First, we needed to know, really, how much water the dishwashers and the sinks required and at what temperature. The dishwashers, though old, were from "the standard" manufacturer and sure enough, the literature was available on the Internet. Then we calculated how much water each sink would hold and asked what a reasonable time would be to fill each one. The dishwashers each required 5 gallons per minute at 180°F. Simple math says that's 10 gpm. Each of the 8 stainless steel sinks (1 faucet per 2 sinks, though) could hold 25.2 gal and a 5-minute fill would be acceptable. More simple math: 25 gallons/5 minutes gives another 5 gallons per minute times 4 faucets yielded another 20 gallons per minute at 130°F.
So we had calculated that the hot water demand was 20 + 10 or 30 gallons per minute. From our other work at the camp, we knew that the well wouldn't produce thirty gallons of COLD water per minute, but they've never reported running out of water. Our first learning moment of the day was when we found out that a kosher kitchen, despite having two of all of these appliances, only used one side to serve and clean up any single meal. This cut the water flow requirements down to a considerably more modest fifteen gallons per minute, though how we would safely supply two different temperatures was still in doubt.
The Search Begins
Armed with this information, we began our search for tankless hot water heaters that would meet all of these requirements. However, it turned out that we needed even more information. Our camp is located in a region where the water contains calcium carbonate or lime. This is the white scale or platy stuff that you may see on the inside of the dishwasher or coffee pots or other hot water contact areas.
Generally not a health problem, it can create significant maintenance and operational concerns by accumulating inside of hot water heaters and the dishwasher jets and heating elements. The amount of dissolved lime is referred to as "hardness." Because of the tendency to foul the equipment, the heater and the dishwasher manufacturer had hardness qualifiers in their literature. Upon examination of the inside of the dishwasher, particularly the jets and tank heating unit, it was pretty clear that the water was indeed very hard.
We discovered the need to have a water analysis done to quantify the hardness, because a water softener to lower the dissolved mineral content was on the horizon. After the technician took samples (a free service!), we knew what the capacity of the softener would be, and we could choose the right unit. We decided to only soften the water that would be heated, since there were no other quality issues with hardness in the cold tap water.
The last bit of data we needed was the temperature of the water coming into the heater. It turned out that the temperature rise was a larger consideration than the finished water temperature. Each unit is designed to increase the temperature at a certain flow rate, and each manufacturer publishes a graph that shows the relationship for its products. One commercial unit we found can increase the temperature 90°F at 8 gpm. If we assume that the water coming from the well is about 50°F, we can expect that the unit can deliver 8 gpm at 140°F. For lower increases in temperature, the flow rate goes up. For greater increases in temperature, the flow rate goes down. We settled on one that could deliver our required 10 gpm at 130°F. Not only that, but this same model could deliver a 130°F rise at 5 gallons per minute. Using the same calculation as before, we saw that one of these could produce the 130°F + 50°F = 180°F water at 5 gpm for the dishwasher.
The only task left in the conceptual part of the project was to arrange the components schematically to ensure that all of them were compatible for the conditions and their desired performance and to identify a location for them to be installed. Our preliminary layout is shown in Figure 1.
The sketch shows splitting the cold water supply just before the water softener. The cold water would be distributed as it always had been, and the water to be heated would flow through the softener where the lime and other minerals that would foul the inside of the water heaters will be removed. After softening, the line splits again where each part passes through identical heaters, but which are set for different temperatures.
How Is This Really Built?
With the dimensions of the selected equipment in hand, we looked for smart places to install them. With the boiler and storage tanks removed from the cinder block building, that seemed to be the best first place to look. Despite the lack of a drain in the cinder block building, we found an inlet nearby for the softener to discharge the backwash water when it regenerates itself. That would allow the controls to be installed out of the weather and for storage of the salt with room to spare. The two heaters (30"x 20"each) are installed on the outside wall of the kitchen where they can be easily served with new propane supply lines and drained to the ground of the 0.6 gallons of water that normally remains in the unit. The thermostats can be either outside at the units (for ease of maintenance) or inside the kitchen (for ease in operation). New hot water supplies will need to be run to the dishwashers from the heater, but since all of the piping is exposed in this painted block and open frame building, that doesn't promise to be difficult or expensive either.
How Much Will This Cost?
The new hot water heaters and the softener will cost on the order of $5,500. All of the piping and the equipment will be installed by Ed. Setup, initial adjustment, and training on the equipment by the vendors are all included in the equipment price. Even so, $5,500 will buy a bunch of plain old conventional hot water heaters. Our final step before we order the equipment will be to look at the operating costs (in terms of propane, deliming solution, etc.).
During this summer, the kitchen manager will qualitatively track how long the dishwashers run for each meal and will forward the kitchen's propane bills to us. With that information, we'll be able to say with much more certainty what the propane and water savings should be with the tankless arrangement, and therefore compare costs over the lifetime of the alternatives. Maybe the final analysis will show that the costs are quite similar, or that money could be spent to purchase two life cycles of conventional heaters for each one life cycle of the tankless heaters. But ultimately, the leadership of camp will be able to make a well-informed decision based on a thorough, realistic comparison of feasible options.
I suppose that the lesson here may be that the next time that camp is faced with replacing existing systems, why not consider newer technology? You may find that there is indeed a better way to "skin the cat."
Rick Stryker is a professional engineer with Camp Facilities Consulting, providing study, design, permitting, and construction consultation services to the camp and conference center community. Camp personnel may contact him at 570-296-2765 or by e-mail at email@example.com.
Originally published in the 2005 September/October issue of Camping Magazine.