Batch Solar Water Heaters Tom Lane The simplest type of solar water heater is a "batch" heater, so called because the collector is the storage tank Ä water is heated and stored a batch at a time. Batch heaters are usually used as preheaters for conventional or instantaneous water heaters. When hot water is used in the household, solar- preheated water is drawn into the conventional water heater. A batch solar water heater is a low cost alternative to an active solar hot water system, offering no moving parts, low maintenance, and zero operational cost. The acronym for a batch type solar water heater is ICS meaning Integrated Collector and Storage. Good Freeze Protection for Mild Freezes Thermosiphon units (with separate tank and collectors) have serious problems with their collectors freezing and bursting, even in areas with only one or two mild freezes a year. Thermosiphon solar heaters depend on electrical power and/or water pressure (for freeze dribble valves) for freeze protection, so woe to you and your solar water heater if the power goes out during a freeze. An ICS unit avoids freeze damage by using 4 inch or larger copper tubing in a double glazed, insulated enclosure. Quite simply, the volume of water in an ICS unit is too large to freeze and burst in a mild freeze. Thermosiphon systems also have problems in hard water areas that batch heaters do not. What to Look for in a Batch Heater ICS units can be a good low cost investment for heating water for 2 to 4 people. Beware: some ICS units are not good value due to design flaws. They may even cause your bill to go up instead of down, from late fall to early spring. Since an ICS holds your hot water storage on the roof overnight, it is absolutely essential that 1) it be double glazed 2) it have a selective low emissivity surface coating (like black chrome) instead of black paint 3) only 1/3 of the tubing be exposed above the insulation and it must be sealed off to prevent convection (see diagram Ä insulation here extends 2/3 up around each tube). I have seen single glazed ICS units with the tubing above the insulation returning water to the tank at 45ø F, while sending water to the house at 70øF. This occurred in central Florida after a night in the low thirties! Unless you live in the tropics, an ICS unit must be double glazed. The upper glazing should be low iron tempered glass - NEVER any plastic, Teflon, or fiberglass glazing. The second layer, about 1" to 1 1/2" down, can be glass or Teflon film, since it won't be exposed to corrosive air pollution, acid rain, hail, pollen, and bird excrement. Phenolic foam board is the best insulation for batch heaters. A second choice might be foil faced polyisocyanurate board. Fiberglass will soak up moisture and lose its insulating properties. Don't buy a fiberglass insulated batch heater unless you live in the desert. Styrofoam is not a good high- temperature insulation Ä it will out-gas. INSERT ILLO: The PT-40CN batch heater Volumetric capacity is also critical on ICS units. You should have at least 40 gallons to justify your investment. Hopefully, a manufacturer will bring out a 4' x 10' unit that will heat 50 or 60 gallons. S.R.R.C. and Batch Barracudas The blackest mark on the solar industry is the solar tax credit era of the early eighties. The most common solar system sold then was a single glazed 20 to 30 gallon ICS unit that was mass marketed by high pressure, direct marketing outfits. They used suede shoe barracudas that could convince an unknowledgeable person that sugar on a cowflop was gold. The Solar Rating & Certification Committee (S.R.R.C.) testing procedures are pretty weak; they do not take into account the higher performance of a well-designed ICS unit. You will want a batch heater that holds heat at night much better than the S.R.R.C. ratings. Poorly designed ICS units, those without double glazing, will have good results by official standards, but will not compete with well designed batch heaters in the real world. Unfortunately, some of these poorly designed units are still being sold. I understand that the European solar water heater test does not include a daytime water draw. Such a test, which records results at the end of the day and measures overnight losses, is a much better indicator of performance of a solar system. Hopefully, the S.R.C.C. will come to its senses and adopt the European model, since most homeowners are not able to use hot water during the middle of the day. Choose Copper The ICS tubing should be made of copper. During the early eighties, a lot of ICS units were made from stainless steel. Manufacturer after manufacturer either went out of business or changed to copper. This was due to the massive leaking problems seen after a few years, through the welds of stainless tubes. Historically, all the ICS units made out of type L copper have had no problems and will probably last 100 years or longer. If you don't get a full ten year warranty that includes both parts, shipping, and labor, then look for another company. Make sure your run to and from the batch heater is all in 3/4" soft type L copper. Unlike hard copper, soft type L copper can expand about twice its diameter. Insulate the pipe with 3/4" elastomeric insulation (Rubatex or Armaflex) available at heating and air conditioning supply outfits. Specify 7/8" inner diameter with 3/4" or 1" wall thickness. Do not use polyethylene insulation, it will melt. Wrap all exterior lines in aluminum tape and spray with a can of automotive undercoating paint. You can tee or branch off the solar return leg of a ICS unit in the attic and go to a second or even a third water heater in the home. Freeze Protection My major concern about ICS in the extreme north is that the water in the lines going to and from the unit will burst in the winter. The Dole corporation makes a thermally activated dribble valve that goes on the exit from the ICS unit (available at most solar water distributors). Currently, there is nothing available to protect the pipe that supplies water to the ICS unit. Batch heaters can be cost effective in northern climates if your are careful to drain the batch heater during the cold season when there's a chance of the pipes freezing. Don't worry about mild freezes. You could use a stove or fireplace heat exchanger during that period for heating your hot water. You need to adapt your lifestyle to get the most out of an ICS unit when the weather is cool. In the Sunbelt, during the winter, it is important to use most of your water from 10:00 am to 8:00 pm to take advantage of the time that the water is hottest. Try to do laundry and dish washing between 10:00 am and 2:00 pm. Cost & Installation You can purchase a 40 gallon, double glazed ICS unit for around $1,600 with mounting hardware or have one completely installed for $2,500 or less by a contractor. ICS units are heavy. They are about 250 pounds dry, and need two ladders and four men or a sign company crane to get them on the roof. However, they are not too heavy for the roof as the weight is distributed over a minimum of 32 square feet spread out over two trusses or rafters. Summary An ICS unit can be a good investment. However, do not rely on the S.R.C.C. BTU ratings alone if you do not want to get "sunburned." You need to make sure you get a well designed, double glazed unit of at least 40 gallons. You must also realize the special limitations of these solar batch water heaters. More than active systems, the total contribution is dependent upon your hot water consumption patterns and daily weather conditions. Batch heaters offer an economical alternative for homeowners with limited budgets and/or small demands on hot water. Access Author: Tom Lane, ECS, 4110 SW 34th St Ste 15, Gainesville, FL 32608 ù 904-373-3220