Water heaters - Tank-less save energy.
Maintenance and engineering managers seeking low energy and water use in their facilities explore many products and technologies. Tank-less water heaters get increasing attention. A closer look at tank-less technology helps managers quantify its benefits. It also lets them understand maintenance and engineering factors in installing, monitoring and maintaining tank-less systems and other technologies. Storage tank water heaters have served institutional and commercial facilities for years. But it is apparent that it can waste over half the potential energy in natural gas. Considering rising energy costs, it may not make sense. In terms of energy used, water heating systems are second only to HVAC systems.
Even small efficiency gains can cause big cuts in energy expenses. To meet increasing market needs, manufacturers now offer new systems, including tank-less, high efficiency condensing tanks and high efficiency instantaneous heaters. Industry standard is a gas heater storing water in a 50-90 gallon capacity tank. Moderate heat slowly transfers to water from gas burner at the tank's bottom and from the hot gases flowing through the tank's center. It uses energy when occupants want hot water, and in maintaining water temperature all day, seven days a week. A tank-less heater uses element that quickly applies high heat to water flowing through the heater. Unlike a tank heater, it does not use energy continually. A tank-less heater can pay for itself in 3 to 7 years. A shower compares two systems. Most shower heads operate at flow rate of 2.5 gallons per minute (gpm). A typical shower valve mixes 80% hot water with 20% cold water. So the water heater produces 2 gpm of hot water.
During the shower, tank heater looses hot water and gets cold water. An old thumb rule is that 80% usable hot water is available in a tank before its temperature drops below comfortable level for shower. A typical shower takes about 10 minutes, so a building with a 50 gallon heater will serve only two showers. In contrast, a tank-less heater provides unlimited hot water as it can provide 2 gpm hot water for as long as water flows through the heater. But it can have problems on a cold winter day, if two showers plus a dishwasher run simultaneously. In this case, water heater will raise water temperature from 40 to 120 degrees, so a typical single tank-less heater cannot supply enough hot water.
Benefits breakdown Tank-less heaters offer many advantages compared to a tank heater. Tank-less units last longer, take up less floor space, pollute less because of low nitrogen oxide discharge, use less gas, have no tank to dispose of, and offer tighter temperature control - generally, of plus or minus 2 degrees. They also have no time limit on hot water supply at low flows, have no safety issues because of a leaking tank and avoid problems of bacteria growth in stored hot water. Managers should keep following important points in mind when installing tank-less systems: -Gas line size: Gas flow is increased compared to tank type heaters and requires larger piping. -Venting: Most manufacturers provide venting kits with PVC outer pipe with a stainless steel inner pipe.
Gas fired equipment needs an inlet supply of fresh air for combustion, and an exhaust vent. -Location: Heaters can be installed on outside walls with venting through the wall, or they can be installed outside with a special insulated shell. Engg considerations Simple installation is a key factor in selecting tank-less heaters. But some commercial applications need complex designs that may not deliver desired benefits. For example, when hot water fixtures are far from the heater, pumps can circulate water from the longest run of pipe back to heater. As a result, hot water is available at all times to all fixtures. But constant circulation of water in these heaters can shorten the unit's warranty from 10 to 3 years.
To address this issue, managers can specify a small 1.5 kilowatt per hour, 6 gallon storage heater installed in recirculation loop to maintain water temperature. While it solves the problem, it also reduces energy savings. Another remedy is to install more than one heater. In areas with hard water, lime deposits can accumulate at heating element, reducing its efficiency during low flows. To address the issue, manufacturers recommend cleaning fixtures every few years or installing water softeners. Some models have sensors that notify when the unit needs cleaning. It also is essential that managers and operators keep water flow rate in mind. Inlet cold water temperature can be as low as 40 degrees in some winter conditions. Energy used by heater is directly related to temperature difference between water entering and leaving the heater.
Tank-less heaters are limited by the energy they use. Most heaters provide 8 gpm at 120 degrees, but if higher temperatures are needed, amount of hot water drops. It is important to know the temperature and flow of hot water to find a heater that meets these demands. When demand exceeds 6-8 gpm, tank-less manufacturers recommend installing more than one heater in parallel and some also recommend storage tanks. It is important to follow manufacturer's recommendations for each application.
These systems can result in designs with complex installations, operations and maintenance.Tanks with tank-less water heaters can decrease heaters' energy savings when compared to tank type heaters. For example, two tank-less heaters in plumbing that also has a hot water storage tank, will require installing 2 heaters, 1 tank, 9 valves, 3 relief valves, a check valve, a circulation pump and 8 pipe connections. Combining systems could void warranties and lead to complex maintenance issues. If something goes wrong in the system, whom will the manager call - the installation contractor, tank-less water heater manufacturer, pump manufacturer or an engineer? Some manufacturers suggest that managers use approved contractors to help tackle these issues. When managers understand performance benefits and challenges related to tank-less water heaters, they will be better able to specify appropriate system for application.
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|Publication:||Pakistan Engineering Review|
|Date:||Mar 15, 2016|
|Previous Article:||Improving energy efficiency.|
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