From: Nadav Malin, BuildingGreen, More from this Affiliate
Published September 20, 2007 06:34 PM

Phoenix Solar Tank Does it All — Efficiently

The basic Phoenix water heater from Heat Transfer Products (HTP) combines multiple features—including the integration of space and water heating—in one efficient package.

The unit’s modulating burner and condensing flue provide residential hot water with an impressive 97% thermal efficiency using natural gas or liquid propane. Auxiliary hookups for a heating coil can be used in forced-air or radiant heating systems. The new Phoenix Solar has a second heat-exchange coil inside the tank for fluid from solar thermal panels.

This feature means that one tank can serve as both the primary and the backup storage tank for a solar hot water system. Storing both solar-heated water and gas-heated backup water in the same tank simplifies installations dramatically, but it could compromise the efficiency of the system. If the fluid loop serving the solar collectors encounters water in the tank that is kept warm by the gas backup system, it would force the solar collectors to operate at a higher temperature, reducing their efficiency. HTP has mitigated this problem, however, by placing the solar loop at the bottom of the tank and the gas burner halfway up. In this configuration, the water stratifies in the tank, so the bottom remains cold. “We’ve measured and found cold water at the bottom of the tank, even with water at 115°F (46°C) at the top,” claims David Davis, president of HTP.


Any loss in efficiency may also be offset by the increase in the amount of solar energy provided to the system from the larger tank, compared with a dedicated solar tank. In addition to solar panels, fluid from a heat exchanger connected to a wood-burning stove or other heat source can also be used to preheat water in the tank. Phoenix Solar is available in 80-gallon (300 l) and 119-gallon (450 l) sizes. It has two inches (50 mm) of foam insulation, and can be installed with zero clearance to combustibles. The auxiliary connections for a heating coil are especially useful for low-temperature heating applications, such as a radiant slab. If higher temperatures are required, a mixing valve would be needed to reduce the temperature for sinks and showers.

The system can be configured with an outdoor temperature sensor to boost the water temperature only during the heating season, according to Davis. “I really like the auxiliary connection ports—it’s something I often struggle with, so it’s nice to see they thought of it,” said Marc Rosenbaum, P.E., of Energysmiths in Meriden, New Hampshire. While the unit is too new to have much field experience, it’s based on the well-established Phoenix water heater, so chances are it will be a winner.

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