Atlas Water Heater Frequently Asked Questions
What are the best applications for the Atlas?
The Atlas is best designed for low temperature applications, although it can be used for applications with outlet temperatures up to 250 deg F. The highest efficiencies will be seen at lower temperatures, such as snow melting, pool heating, and outdoor athletic field heating, and low temperature building loops. In order to get the best efficiency out of the Atlas, building loops should be run at lower temperatures since condensation is not a concern. This lower building loop temperature will lead to less insulation around the pipes because of the lower differential between the ambient air and the water.
What is the advantage of a condensing water heater?
The advantage of a condensing water heater is higher efficiency. Traditional non-condensing products have efficiencies of up to 86%, while the Atlas can have efficiency up to 97%. To understand why a condensing water heater has higher efficiency, one must first understand that condensation is the process of gas is cooling enough to change into a liquid. During this process, heat is given off without having to add any more energy to the system. If this condensation occurs inside the heat exchanger then the overall efficiency of the unit will increase. The lower the inlet temperature, the more the unit condenses, and therefore the higher the efficiency. Traditionally, condensing was avoided because it would cause damage to the water heater, but condensing products are designed to withstand the corrosive condensate of the flue gases caused by combustion. Ace Heaters uses a protective coating on the coils in combination with a stainless steel combustion chamber to withstand this corrosive environment.
How does this model of Atlas A vary from Atlas GS?
Many improvements were made from the GS model, but here is a list of the most important changes. The first improvement that was made was reduced pressure drop. Ace Heaters accomplished this by redesigning the coil assembly to greatly reduce turbulence by eliminating tees and elbows and redesigning the manifold. The combustion assembly was also changed to allow for better turndown and more consistent performance. We added more insulation to the areas that were found to be hot spots. The biggest performance change was going from a direct spark surface igniter to an interrupted pilot. This change has allowed Ace Heaters to provide a much more consistent product to the customers.
Can Atlas be guaranteed to get the same efficiency as the published value?
The published efficiency is based on in-house testing of several water heaters averaged over many months tested under real world conditions. Many installation factors can affect the efficiency of the water heater such as the inlet temperature, ambient temperature, humidity, excess air, and the quality of the water. If the installation location was able to duplicate the same conditions the water heaters were tested under, then it would achieve the same efficiency as is published. While it is nearly impossible to duplicate the same testing conditions, the good news is that the customer can have better conditions, which will lead to higher efficiencies.
What is the square footage of heating surface on the Atlas heat exchanger?
|MODEL||SQUARE FOOTAGE||VOLUME OF WATER|
|A050||107 ft2||2.4 gallons|
|A075||165 ft2||3.7 gallons|
|A100||224 ft2||5.0 gallons|
|A150||321 ft2||7.1 gallons|
|A200||424 ft2||9.4 gallons|
|A250||537 ft2||11.9 gallons|
|A300||650 ft2||14.4 gallons|
What are some important factors in comparing the efficiency of the Atlas to other manufacturers?
In order to compare the efficiency of the Atlas to other manufacturers, it is important to compare the units under similar conditions. The Atlas units were tested for efficiency at 35% excess air in order to maintain NOx levels under 10 ppm (normally in the range of 5-7ppm). As the excess air is decreased, the NOx levels will increase, but the efficiency of the unit will also increase. Also, the average ambient temperature when testing the Atlas was 85 degrees. Another important factor is the firing rate of the water heater. On low fire the Atlas is at approximately 15% fire. Other companies claim to go as low as 5% fire. While this will give a higher efficiency, we do not believe 5% fire be achieved in the field on a consistent basis, hence we believe this data to be impractical and somewhat misleading. The reason why Atlas is not tested at a lower firing rate is discussed below in “Why can’t Atlas achieve the high turndown of other manufacturers.”
What is the turndown ratio of each of the Atlas models? Click here to get a hard copy of our Tech Talk for high turn down ratios.
Why can’t Atlas achieve the high turndowns of other manufacturers?
As a standard, Atlas can get up to 7.5:1 turndown, with the A300 and A150 being our best performing units. We limit our turndown ratio to what delivers consistent, solid performance for our customers. While the Atlas can get a lower input, and therefore higher turndown, the lower input is impractical, as it sacrifices the consistency of units operation/performance. The question is not tuning the unit for the highest possible turndown, but rather tuning the unit for the highest turndown without sacrificing performance and reliability for daily operations. A unit may be capable of higher turndown, but evaluating its performance on the basis of consistency and reliability is the more sound approach.
What can I do, if I want to get a higher turndown with the Atlas unit?
If higher turndown is desired, multiple smaller Atlas units can be used instead of one large Atlas unit. For example, two Atlas A150 units can be used in place of an Atlas A300. This configuration can achieve a turndown of up to 15:1 with the same BTU input output compared to the single Atlas A300.
Why do I need to list the feet of venting and gas inlet when I place an order?
First, the best recommendation to avoid the high costs of venting is to install the Atlas as close as possible to and outside wall and directly vent the Atlas outdoors. When an order is placed, this information is very important because it determines how the technician tunes the unit. To give an extreme example, if it was assumed that the customer had 5 inches of gas pressure and they actually had 16 and didn’t make any adjustments, then their efficiency would drop by almost 6% and would be getting a higher input than expected. The venting information is also important because the more venting the customer has, the higher the chamber pressure. If the chamber pressure is too high (above + 0.4 in WC) then it could cause problems with the pilot. If it is known that the customer is using several feet of venting, say 70 feet of intake and exhaust venting (we recommend 30 feet of each or less, but up to 60 is fine), problems can be prevented by enlarging the intake and exhaust vents. In addition, increased intake venting will have an effect on the input of the unit because of the restriction of air flow into the blower. By knowing this information, the customer is assured that they will receive a unit that will work for their application, and prevent a lot of installation problems.
Why is the Atlas flow rate so limited?
The flow rate for the Atlas is based on the maximum velocity allowed by the copper fin tube manufacturer. The manufacturer suggests 8 ft/sec as the highest velocity of water, although depending on the application it could be even slower. The Atlas design uses 2 tubes running in parallel on A050-A150 and 4 tubes running in parallel on A200-A300. So as a result of the limited area for the water to flow, the flow rate is limited. Other manufacturers that allow for higher flow rates have a tube sheet design, which is often a fire tube design, which allows for more tubes inside of the water heater. The disadvantage of the tube sheet design is inconsistent water flow and increased chance of thermal shock. In a traditional tube sheet design higher velocities in some tubes can cause erosion, while the tubes with the lower velocities can form scale which will lead to lower efficiencies and overheating. The tube design of the Atlas allows for consistent water flow through each coil and consistent heating, along with no chance of thermal shock. In addition, with increased flow rate, the temperature control becomes less precise, so even if a product can handle flow rates in the 300 gpm range, that doesn’t mean that the heating of that much water can be accurately controlled. If a system is set up for high flow rates, then an Atlas can be installed in a primary-secondary loop. Ace Heaters can provide a diagram with recommended flow rates through both loops upon request.
What is the derating factor for the Atlas?
The Atlas water heater should be derated 2.6% for every 1000 feet of elevation based on factory testing and calculations. For an elevation of 5000 feet, the deration shall be approximately 8% with the blower making up for 40% of the deration. The blower speed of the Atlas can be increased to accommodate for some of the deration by bringing in more air, and therefore more oxygen molecules. The 2.6% deration is primarily based on calculations of the amount of oxygen molecules per volume of air at different elevations combined with engineering knowledge of Atlas performance. With an input of 3,000,000 BTU/hr, the available derated input would be approximately 2,760,000 BTU/hr. For 60oF inlet water, the efficiency equals 93.5%, which results in an output of about 2,580,000 BTU/hr. As the temperature of the water decreases, the efficiency of the unit increases because of the increase in condensation and the ability of water to absorb more internal energy (heat) at lower temperatures. The requirement for the 96% efficiency used in the original calculation is based on the unit running at low fire. In addition, the atmospheric conditions including the humidity in the air and the temperature of the air have an effect on the output of the water heater. Also the amount of intake and exhaust venting on the unit may have an effect on the output of the water heater. Atlas efficiencies are based upon performance at sea level with average temperatures around 80oF with excess air at 35%. Therefore, the 8% deration of the water heater is based on reasonable engineering projection of how the Atlas will perform.
What are typical flue gas temperatures?
Typical flue gas temperatures range between 75-160 degrees on low fire and 175-275 degrees on high fire. These temperatures are highly dependent on the firing rate of the unit and the temperature of the air.
What is the minimum circuit breaker size for the Atlas?
The maximum amps for the Atlas is 15, but this can vary depending on the unit and the back pressure because the highest amps are from the blower. The standard options will not exceed the 15 amps unless a pump is added which will add up to 10 more amps.
Can the Atlas water heater be operated in hydronic applications?
The Atlas Water Heater is certified for both water heating and hydronic applications.