By Rich Grimes Water Solutions Marketing I am constantly asked questions from contractors related to water heating and water systems. In this issue I will address some Frequently Asked Questions that come up more often than others. 1) What is the most efficient way to heat water – Gas or Electricity? Electricity is more Read more
Rich Grimes
By Rich Grimes
Water Solutions Marketing
I am constantly asked questions from contractors related to water heating and water systems. In this issue I will address some Frequently Asked Questions that come up more often than others.
1) What is the most efficient way to heat water – Gas or Electricity?
Electricity is more available to consumers than Natural or Propane Gas. Natural gas is an interconnected system of piping that services certain areas. Customers have access to Propane if Natural is not available in their area.
As far as efficiency, Electric resistance immersion heating is 98% efficient. Gas-fired appliances have efficiencies ranging from about 80% all the way up to 98%. The best answer to this question is Electricity is more efficient with a higher energy cost. Gas is typically less efficient but has a lower energy cost. The lower efficiency gas-fired heater costs less to operate than a comparable electric model. The new Hybrid Heat Pump heaters are the least expensive way to heat water if you are comparing them to a standard tank-type heater with either electric or gas input.
2) What about the Hybrid Heat Pump water heaters? Are they a viable option to heat water with electricity?
Absolutely – The Heat Pump water heaters use approximately one-half of the electricity of a standard electric water heater. Instead of using a 4500 Watt element to heat the tank, a dedicated heat pump can generate plenty of hot water with its 850 Watt heat pump assembly.
There are many benefits to using a heat pump. Many electric providers offer rebates for replacing standard electric water heaters with Heat Pump technology.
3) What are the benefits of using Tankless water heaters?
Tankless gas and electric products are flow-activated and do not heat any water (or use fuel) when hot water is not being used. They do not experience any of the stand-by losses associated with a tank-type heater. The other key features are wall mounting, compact size and continuous hot water on demand.
The electric models are better suited to point-of-use at the fixture and can be located under a sink, on a wall or in a cabinet. The gas-fired tankless heaters have more output and can handle large loads. They also can be linked together to create modular systems with multiple heaters for even larger hot water loads.
4) What is the main cause of water heater failure?
Lime scale build-up on heating surfaces is the most common contributor to heater and tank failure. It is also the reason that heaters use more energy over time. As the heating surface accumulates more film thickness of scale, it requires more energy to heat the water through the scale. A gas-fired heater must keeps its burner on longer and an electric heater must keep its elements on longer to heat the same amount of water, through the lime scale insulator. The combination of metal stress and fatigue and long burner cycles caused by scale build-up will cause premature failure.
5) Can a water heater be descaled to prevent premature failure?
Scale is very hard to remove on a tank-type heater. The commercial tank-type heaters can accumulate quite a bit of precipitated calcium carbonate.
Tankless and coil type heaters can be cleaned to remove the lime scale. A small pump with a bucket of vinegar can circulate the heat exchanger until the scale build-up has been removed. There are also specific non-toxic cleaning solutions that are available to clean copper coils and heat exchangers like citric acid.
The descaling process is much more complicated on gas tank-type heaters and is rarely performed on them. On electric heaters, the scale builds up on the elements and does precipitate into the tank. An electric heater can be blown down at the drain valve and have the elements cleaned or replaced, which is a typical tune-up.
6) How can a gas-fired appliance be able to be vented with plastic vent pipe such as PVC or CPVC?
PVC piping is rated for a maximum temperature rating of 140°F and CPVC is rated for 180°F. These temperatures are much lower than the actual combustion exhaust temperature.
There are two predominant methods that are utilized to allow for plastic venting on gas heaters:
The first method is air dilution where a fan-assisted vent assembly with allow cooler ambient air to mix with the combustion exhaust. This method is commonly seen on residential Power Vent water heaters.
The second method that is more common is a High Efficiency appliance that uses an exhaust heat exchanger to preheat the incoming cold water or a multi-pass flue assembly. As cold water flows through the exhaust heat exchanger or across the multi-pass flue, the exhaust temperature drops and the efficiency goes up! These heaters are rated above 85% and usually in the 90%+ efficiency range, extracting almost all of the latent heat from the combustion process. The by-product of the high efficiency exhaust is water vapor that condenses and requires removal from the heater and vent system typically by a condensate trap assembly.
There is some contention on the use of plastic piping for heater exhaust. It should be noted that heaters are produced with various safety controls including exhaust high limits, vent sensors and pressure proving switches. These devices insure that the heater will be disabled if a high exhaust temperature is sensed. This will protect the plastic exhaust piping until the condition can be rectified.
Another important note regarding plastic venting would be to always use PVC or CPVC Schedule 40 or 80 solid-core pipe and pressure rated fittings. NEVER use foam-core pipe on a sealed vent exhaust system. Other plastic piping materials such as Polypropylene have higher temperature ratings and can be used for sealed venting but they can be cost prohibitive. Sealed SS Category III and IV vent pipe also are rated for use on high efficiency appliances so they are an option where piping may run through a return air plenum.
7) What are the essential considerations to perform a successful installation of a Gas water heater?
Every gas appliance installer should have an understanding of the unit’s requirements in the following areas:
a) GAS SUPPLY – verify gas type, BTU inputs, pipe sizing, pressure regulation, etc.
b) COMBUSTION AND VENTILATION AIR – verify gravity air intake or Direct Air requirements specific to the installation, per manufacturers specifications and NFGC/NFPA54.
c) EXHAUST SYSTEM – verify approved vent material, vent lengths and termination. Verify that the vent route does not conflict with clearances, existing code or other trades.
d) ELECTRICAL – verify required voltage, polarity, disconnects, breakers, etc. Most electronic heater controls require 120V which is stepped down to 24VAC for the safety controls. Hot Surface Ignition systems typically use 120V to heat up the igniter.
There are other aspects of a gas heater installation that are also important such as clearances from combustibles. A little planning goes a long way! Read the instructions!
8) Do I need an Expansion Tank on my water heater?
Expansion tanks are designed to absorb thermal expansion created when heating water. If you have a check valve or backflow device located near the water heater you will need an Expansion Tank. These positive shut-off check valves will not allow expanding water to go anywhere. The heater tank must absorb the expansion which leads to premature tank failure. A relief valve that opens at the end of a heating cycle is a definite sign of the need for expansion control.
The answer is that an expansion tank or device may or may not be required but it is always a good idea. It greatly reduces vessel stress and prolongs water heater life. It is very important on commercial heaters that have high volumes of expansion.
9) My old heater was 12 years old and I never needed an expansion tank. Why do I need one now with this brand new water heater?
This is more common than you might think. The old heater was scaled up and had a long heating cycle. The expansion is spread out over that long heating cycle. The new heater has a clean heating surface and a much quicker recovery time. This cycle can be half as long as the old heater due to lime scale build-up. The expansion occurs much quicker than the old heater.
This is why expansion control is so important on commercial heaters. An atmospheric heater rated at 500,000 BTU with an 85 gallon tank can recover approximately 480 GPH and raise the temperature 100°F. But wait, 480 GPH ÷ 85 Gallons = 5.65 Minutes… In less than 6 minutes the burner can raise the tank temperature from 60°F up to 160°F! That is rapid expansion that will stress a commercial heater each time the burner fires.
This has been a little different format but I hope you got something out of it. We are always open to questions so please let us know of any issues or topics that we could discuss.
Thanks and we’ll see you in a future article!
Rich Grimes
by Rich Grimes Water Solutions Marketing I have had many projects where lack of combustion/ventilation air has been the issue. It reminds me of how many installations I have seen like this. Surely more than I can remember… Lack of air on a water heater is similar to lack of air on a car or Read more
by Rich Grimes
Water Solutions Marketing
I have had many projects where lack of combustion/ventilation air has been the issue. It reminds me of how many installations I have seen like this. Surely more than I can remember… Lack of air on a water heater is similar to lack of air on a car or small engine. Poor combustion results in lost efficiency and more hazardous emissions. Symptoms such as sooting and constant flame failures can be indicators of air issues. Imagine a candle snuffer that does not touch the wick of the candle, but it captures all of the heat from the flame. The flame uses up all of the air inside the small candle snuffer and the flame cannot maintain combustion. Soot is produced as the fresh air is used up by the flame. Gradually, the flame is extinguished due to lack of combustion air.
In this article we shall discuss combustion and ventilation air requirements for gas-fired appliances. Combustion and Ventilation Air requirements are set forth in the National Fuel Gas Code and typically apply to Atmospheric or Fan-Assisted Combustion. As we discussed in previous articles regarding venting, Category IV appliances typically have a direct air intake from outdoor, negating the need for separate combustion/ventilation air louvers in the wall or door. Separate Air Intake systems for gas-fired appliances are specified by the manufacturer and must be part of the vent system approval.
PRINCIPLE
Gas-fired appliances require adequate Intake Air for Combustion and Ventilation. There are two methods for sizing Intake Air. The Standard method is used almost exclusively, requiring a minimum volume of 50 cubic feet per 1,000 BTU/hr. The second is the Known Air Infiltration Rate Method. This method is rarely used and requires calculations based on atmospheric or fan-assisted combustion and air change per hour.
The movement of air between two louvers allows fresh air to enter the mechanical room and be circulated. A larger, single louver can be utilized to allow enough air to enter and circulate. Each particular air intake arrangement has its own sizing based on the total BTU input of all appliances in the room and where the air is communicated from. The sizing of combustion and ventilation air is specified in the National Fuel Gas Code / NFPA54 / ANSI Z223.1 Section 9.3.
REQUIREMENTS
The intake air sizing is based on the total BTU input of all appliances and is determined by the following installation parameters:
AIR FROM OUTDOORS (TWO PERMANENT OPENINGS)
This method requires two (2) permanent openings. One opening is located within 12 inches of the top of the enclosure and the other is located within 12 inches of the bottom of the enclosure. These openings must communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors:
1) Where communicating directly with the outdoors (LOUVERS) or through VERTICAL DUCTS, EACH opening shall have 1 Square Inch per 4,000 BTU/hr, the total of all appliances.
Example: 200,000 BTU Heater = 200,000 ÷ 4,000 = 50 Square Inches Free Area per opening.
2) When communicating directly with the outdoors through HORIZONTAL DUCTS, EACH opening shall have 1 Square Inch per 2,000 BTU/hr, the total of all appliances.
Example: 200,000 BTU Heater = 200,000 ÷ 2,000 = 100 Square Inches Free Area per opening.
AIR FROM OUTDOORS (ONE PERMANENT OPENING)
This method requires one (1) permanent opening. This opening is located within 12 inches of the top of the enclosure. This opening must communicate directly, or by Vertical or Horizontal ducts, with the outdoors or spaces that freely communicate with the outdoors:
1) Where communicating directly with the outdoors (Louvers) or through Vertical or Horizontal Ducts, EACH opening shall have 1 Square Inch per 3,000 BTU/hr, the total of all appliances.
Example: 200,000 BTU Heater = 200,000 ÷ 3,000 = 66.67 Square Inches Free Area opening.
2) The minimum free area must be not less than the sum of the areas of all vent connectors in the space.
AIR FROM INDOORS (TWO PERMANENT OPENINGS ONLY)
This method requires two (2) permanent openings. One opening is located within 12 inches of the top of the enclosure and the other is located within 12 inches of the bottom of the enclosure. These openings must communicate directly via Louvers, with an indoor space that is adequately ventilated:
1) Where communicating directly with another interior space, ON THE SAME STORY, VIA LOUVERS, EACH opening shall have 1 Square Inch per 1,000 BTU/hr, the total of all appliances.
Example: 200,000 BTU Heater = 200,000 ÷ 1,000 = 200 Square Inches Free Area per opening.
2) Where communicating directly with another interior space, ON A DIFFERENT STORY, VIA LOUVERS, EACH opening shall have 2 Square Inch per 1,000 BTU/hr, the total of all appliances.
Example: 200,000 BTU Heater = 200,000 ÷ 500 = 400 Square Inches Free Area per opening.
ALTERNATIVES
There are a few options available such as engineered installations and mechanical air intake fans. Mechanical air intake systems can provide a controlled air intake. These systems employ a Power Air Fan that will force fresh air in at a given CFM. These must be interlocked with ALL appliances to insure that combustion air is being provided and proved prior to burner ignition. There are also many products that can utilize Direct Air Intake through a fan-assisted/power burner combustion process and separate air intake pipe. These heaters and boilers have become very popular because of their multiple vent and air capabilities. High Efficient appliances that utilize PVC and other plastic vent materials are great options when combustion air is limited.
CONSIDERATIONS
Many restaurants operate in a negative pressure within the building. This is mainly due to exhaust hoods that extract smoke and fumes from cooking. These exhaust fans are extremely strong and can cause burner operational problems. They will draw up and consume the combustion air needed for proper operation. If you open a door to the outside, air rushes into the building.
Equipment such as atmospheric stoves operate properly because they are located directly beneath the exhaust hood and all available air is drawn by them. A water heater or boiler that is located in another part of the restaurant can experience sooting, leakage of combustion products and flame failures due to this lack of air. The big problem is that leakage of combustion products equals spillage of carbon monoxide in the restaurant. The vent stack for the heater becomes an air intake pipe and air is drawn down from the rooftop. When the heater fires, the combustion exhaust spills out at the draft hood as it cannot be drawn up the vent pipe. It is very common to see atmospheric gas heaters choking in this type of installation. A smoke test at the draft hood of the heater will help indicate if flue products are exhausting properly. The test should be performed with the burner on and off and with the door open and closed. A burner that is starving for air will burn very yellow or orange in color. When the air pressure is relieved by opening a nearby door, the burner flame should be blue in color with slight yellow/orange tips.
These situations can be resolved with heaters that allow for direct air intake. Just because there was an atmospheric heater originally installed, replacement may be better suited to a higher efficient heater that allows or requires direct air intake. Restaurants are not the only buildings that can have negative pressures. The same problem can occur in a small mechanical room where an exhaust fan has been installed. This has the same effect, just in a smaller application. Unventilated closets can produce the same problems.
Louvers should also be checked for free area of square inches. Many louvers can restrict the free area and sometimes a larger size louver is required. Mesh screens should not be placed over louver openings as they will clog up and eventually create an air issue. Double-faced louvers can cut free area by one half, requiring twice as large of a surface area compared to an unrestricted, full flow louver.
SUMMARY
All of these are extremely hazardous installations because they put the inhabitants in direct contact with combustion exhaust containing carbon monoxide. Combustion and Ventilation Air is often overlooked and should be investigated and accounted for when installing any gas fired appliance. Combustion and Ventilation Air are crucial to a good, safe installation.
I hope that these articles are helpful to you and we look forward to seeing you in the next issue!
Thanks,
Rich Grimes
KEY WATER HEATING CHARTS AND FORMULAS by Rich Grimes It’s 2012 already and in this issue we will try to give you plenty of information and useful charts related to water heating. I don’t receive many requests so I am glad to accommodate on such a pertinent subject. The best part is that you won’t Read more
KEY WATER HEATING CHARTS AND FORMULAS
by Rich Grimes
It’s 2012 already and in this issue we will try to give you plenty of information and useful charts related to water heating. I don’t receive many requests so I am glad to accommodate on such a pertinent subject. The best part is that you won’t have to read too much from me as these charts and formulas speak for themselves! So here we go…
BTU
A British Thermal Unit (BTU) is a measurement of heat energy. One BTU is the amount of heat energy required to raise one pound of water by 1ºF. Water weighs 8.33 pounds per gallon so we can calculate that one gallon of water requires 8.33 BTU to raise the temperature 1ºF.
BTU CONTENT OF FUELS
ENERGY SOURCE BTU PER HOUR
COAL
1 Pound = 10,000 – 15,000
1 Ton = 25 Million (app.)
ELECTRICITY
1 KW = 3,412
OIL
1 Gallon #1 Fuel = 136,000
1 Gallon #2 Fuel = 138,500
1 Gallon #3 Fuel = 141,000
1 Gallon #5 Fuel = 148,500
1 Gallon #6 Fuel = 152,000
GAS
1 Pound of Butane = 21,300
1 Gallon of Butane = 102,800
1 Cubic Ft. of Butane = 3,280
1 Cubic Ft. of Manufactured Gas = 530
1 Cubic Ft. of Mixed = 850
1 Cubic Ft. of Natural = 1,075
1 Cubic Ft. of Propane = 2,570
1 Pound of Propane = 21,800
1 Gallon of Propane = 91,000
HORSEPOWER
1 Boiler Horsepower (BHP) = 33,475 BTU
1 Boiler Horsepower (BHP) = 34.5 Pounds of Steam @ 212ºF
1 Boiler Horsepower (BHP) = 9.81 KW
COOLING
1 Ton of Cooling = 12,000
GAS INFORMATION
NATURAL PROPANE
Specific Gravity = 0.62 1.52
Flammability Limits (GAS/AIR Mixture) = 4%-14% 2.4%-9.6%
Maximum Flame Propagation (GAS/AIR Mixture) = 10% 5%
Ignition Temperature = 1200ºF 950ºF
1 Pound of Gas (1 PSI) = 28″ Water Column (w.c.)
1 Pound of Gas (1 PSI) = 16 Ounces (oz.)
1 Therm = 100,000 BTU
ELECTRICAL INFORMATION
1 Kilowatt (kW) = 3412 BTU Per Hour
1 Kilowatt (kW) = 1000 Watts Per Hour
1 Kilowatt Hour (kWH) will evaporate 3.5 pounds of water from and at 212ºF
Amperage – Single Phase (1 Ø) = KW x 1000 or WATTAGE
VOLTAGE VOLTAGE
Amperage – Three Phase (3 Ø) = KW x 1000 or WATTAGE
VOLTAGE x 1.732 VOLTAGE x 1.732
WATER HEATING FORMULAS
BTU Per Hour Requirement
BTU OUTPUT = GPM x Temperature Rise x 8.33 Lbs/Gallon x 60 Minutes
BTU INPUT = (GPM x Temperature Rise x 8.33 Lbs/Gallon x 60 Minutes)
% Efficiency
Heat Transfer Efficiency
% EFFICIENCY = (GPH x Temperature Rise x 8.33 Lbs/Gallon)
BTU/Hr INPUT
Heat-Up Time
Time in Hours = (GPH x Temperature Rise x 8.33 Lbs/Gallon)
(BTU/Hr INPUT x % Efficiency)
Temperature Rise
Temp. Rise (∆T) = (BTU/Hr INPUT x % Efficiency)
(GPM x 60 Minutes x 8.33 Lbs/Gallon)
GPH Recovery
Electric = (kW INPUT x 3412 BTU/kW x % Efficiency)
(Temperature Rise x 8.33 Lbs/Gallon)
Gas = (BTU/Hr INPUT x % Efficiency)
(Temperature Rise x 8.33 Lbs/Gallon)
MIXED WATER FORMULA
% of Hot Water Required = (Mixed Water ºF – Cold Water ºF)
(Hot Water ºF – Cold Water ºF)
WATER INFORMATION
1 Gallon = 8.33 Pounds
1 Gallon = 231 Cubic Inches
1 Cubic Ft = 7.48 Gallons
1 Cubic Ft = 62.428 Pounds (at 39.2ºF – maximum density)
1 Cubic Ft = 59.83 Pounds (at 212ºF – boiling point)
1 Ft of Water Column (w.c.) = .4333 PSI
Water expands 4.34% when heated from 40ºF to 212ºF
Water expands 8% when frozen solid
OPEN VESSEL
BOILING POINT @ 0 PSI ALTITUDE
212ºF 0 Feet (Sea Level)
210ºF 1000 Feet
208ºF 2000 Feet
207ºF 3000 Feet
205ºF 4000 Feet
203ºF 5000 Feet
201ºF 6000 Feet
199ºF 7000 Feet
CLOSED VESSEL BOILING POINT @ PSI @ Sea Level
BOILING POINT GAUGE PRESSURE
212ºF 0 PSI
240ºF 10 PSI
259ºF 20 PSI
274ºF 30 PSI
287ºF 40 PSI
298ºF 50 PSI
316ºF 70 PSI
331ºF 90 PSI
ONLINE RESOURCES
There are an unlimited number of online tools and calculators for every mathematical formula. The internet is full of helpful resources to get the job done quicker. Here are a few links to some useful websites:
WEBSITE/PROGRAM WEB ADDRESS
Amtrol Expansion Tank Sizing http://amtrol.com/support/sizing.html
Engineering Toolbox Calculators http://www.engineeringtoolbox.com/
State Water Heater Sizing (Online) http://www.statewaterheatersizing.com/
AO Smith Water Heater Sizing (Online) http://www.hotwatersizing.com/
Lochinvar Water Heater Sizing (Download) http://www.lochinvar.com/sizingguide.aspx
Cylinder Calculator (Storage Tanks) / Other Math Calculators http://www.calculatorfreeonline.com/calculators/geometry-solids/cylinder.php
Electrical/Mechanical/Industrial/Civil/Chemical/Aeronautical Calculators http://www.ifigure.com/engineer/electric/electric.htm
B&G System Syzer (Piping/Pressure Drop Tool Download) http://completewatersystems.com/brand/bell-gossett/selection-sizing-tools/system-syzer/
B&G Selection and Sizing Tools (Pumps, Regulators, Steam and Condensate) http://completewatersystems.com/brand/bell-gossett/selection-sizing-tools/
Taco Pump Selection Wizard (Online Pump Selector) http://www.taco-hvac.com/en/wizard_pumps.html
Lawler Mixing Valve Sizing (Online – account setup) http://www.lawlervalve.com/index.php?p=page&page_id=Sizing_Program
DSIRE Database of State/Federal Renewable Energy Rebates http://www.dsireusa.org/
ASCO Valve Online Product Selector (Valves – solenoid, pilot, pneumatic, etc.) http://www.ascovalve.com/Applications/ProductSearch/ProductSearch.aspx?ascowiz=yes
SUMMARY
There is a lot of other information that we could add such as Steam. It is a viable heating source and there are several factors that must be considered such as operating pressure, steam trap and condensate line sizing and so on. We will have to do a separate article on Steam in a future issue.
The charts and information above are all essential to water heating. They are proven mathematical formulas of algebra and geometry. If you input the accurate information then the results will be correct. It is also good to use the online tools and calculators. They are true time savers.
Thanks and we’ll see you in the next article!
Thermal Expansion by Rich Grimes We have covered several topics related to water heating in previous articles and we will continue with the issue of Thermal Expansion. Thermal Expansion will occur whenever there is a heat source and the piping loop is “Closed”. This implies that the piping is operating as a Closed Loop, separated Read more
Thermal Expansion
by Rich Grimes
We have covered several topics related to water heating in previous articles and we will continue with the issue of Thermal Expansion. Thermal Expansion will occur whenever there is a heat source and the piping loop is “Closed”. This implies that the piping is operating as a Closed Loop, separated from incoming fresh water by a check valve of a backflow device. Closed Loop systems typically operate at lower system pressures than incoming cold water pressures. A closed loop heating boiler is a good example of such a system. The water in the closed loop of piping is not potable and must be prevented from backflow into the domestic cold water supply. Once a backflow device is installed and the loop is heated, thermal expansion will occur and must be controlled. This is also an issue on domestic water heaters installed on “Open Loop” piping because of code required BFP devices.
HISTORY
Hydronic heating boilers have always required an expansion tank and the sizing is calculated to absorb the system’s thermal expansion. Water heaters were traditionally installed with no check valve on the cold water supply, so the cold water piping would absorb the expanding heated water. Larger commercial systems would utilize a swing check valve to prevent over-heating of the cold water supply. Plain steel expansion tanks could not be used on fresh water systems so the common practice was to drill a ¼” hole in the flapper of the check valve to allow expanding hot water to escape into the cold water supply. This sounds crazy but it was documented in various manufacturer’s literature and did help to alleviate the problem. But it did not fix the problem.
But along came Backflow Prevention and it created an immediate need for Domestic Thermal Expansion Control. The basis of BFP is to prevent cross contamination, but the result was a “Closed” piping loop that experienced thermal expansion just like a boiler! This is similar to Newton’s Law because for each and every action there is an equal and opposite reaction. All of a sudden there were expansion issues that did not exist before!
Manufacturers of expansion tanks provided tanks with internal bladders that could be pressurized and separated the steel tank from the fresh water. The same tank design was being used on fresh water well systems.
Today, backflow prevention is a standard installation practice on domestic cold water systems. There are various BFP’s and Thermal Expansion devices that can be used, depending on local code requirements.
PRINCIPLE
Water cannot be compressed like air so it will expand, creating more volume. This expansion creates a pressure increase that can be entrapped by a check valve or BFP. Water will expand at a rate of .000023 percent for each degree of temperature rise. This may not seem like a lot but if a 30 gallon water heater was heated from 60ºF to 140ºF (80ºF Rise) it would increase in volume by .55 gallons. The additional ½ gallon of water must expand as the volume increases. If there is not a means of expansion control then the expanding water will lift the relief valve to discharge the additional volume and increasing pressure. Temperature and Pressure Relief Valves will discharge with a condition of 210ºF or 150 Psi. Expanding water can easily exceed the 150 Psi T&P valve rating when heating up a “closed” water heater. This is commonly seen at the end of the heating cycle when the relief valve lifts for several seconds. It is also commonly misdiagnosed as a bad relief valve and the replacement relief valve functions just like the “defective” valve, discharging water.
Expansion is a predominately a pressure issue, but temperature accelerates the expansion. Thermal Expansion, expansion caused by heating. New water heaters have a clean heating surface and can expose thermal expansion where the old heater did not display such signs. I have also seen where houses with ½” piping experience more expansion issues than houses piped in ¾”. This is due to the same rate of volume increase with less piping to absorb the expansion. Old heaters that are full of scale have an extended, slower heating cycle that helps to gradually add the expansion.
This will also make you realize how much expansion can be created by large commercial systems with high BTU inputs.
THERMAL EXPANSION TANKS
Domestic Thermal Expansion tanks are constructed typically of an epoxy coated steel shell. They have a butyl rubber internal bladder that separates the bare steel from the fresh water. They have a connection for connecting to the cold water supply and an air connection for pre-charging the bladder pressure. The bladder pressure MUST be preset equal to or a little greater than the incoming cold water pressure. This is crucial to installing an expansion tank. A setting of 10 Psi greater than measured cold water pressure is recommended to compensate for varying pressures. For instance, a neighborhood typically has a little less pressure in the morning (heavy use time) than it might at 2:00 PM when the water usage is less. Cold water pressure should be measured with a hose bibb pressure gauge or similar dial-type gauge. Almost every expansion tank comes factory pre-charged to 40 Psi. While 40 Psi may be expected on a well system, pressures of 60 to 80 Psi are common in Florida. A tank that is pre-charged to 40 Psi and is installed on a 60 Psi system will be ineffective. The air in the bladder is pushed all the way up into the tank and it cannot absorb any expansion. An expansion tank must be pre-charged with no water pressure present for the proper setting.
The connection of the expansion tank to the cold water supply is also critical. The expansion tank MUST be installed between the heater and the cold water check valve or BFP. The hot water will try to expand away from the heater towards the cold supply where it is absorbed by the Expansion Tank.
Bladder style expansion tanks can be mounted in the most convenient location and piped over to the system, unlike gravity style tanks which must be located at the highest point of the system. Bladder tanks are also smaller in size to an open gravity tank due to their ability to absorb expansion at a higher volume.
Thermal expansion tanks are sized based on volume of water, incoming water temperature and pressure, stored water temperature and possibly some pressure and expansion factors. There are various sizing programs available in print and online. There are probably ten to twenty manufacturers of domestic thermal expansion tanks to choose from. There are also larger bladder type tanks available for commercial applications.
SUMMARY
Domestic Thermal Expansion Tanks are required in most systems today due to backflow prevention devices. These devices provide a solid, positive shut off that will not allow for any thermal expansion. There are also other means of expansion relief, but most involve a self-seating valve that will lift and allow the relief of the additional volume, prior to the heater T & P valve lifting. The Bladder type tanks provide proper expansion protection and also a little protection from water hammer and thermal shock. Systems that experience extreme hammer or thermal shock should be provided with additional protection such as water hammer arrestors or shock absorbers.
It is important to pre-charge the expansion tank and make sure that the connection to the system is located between the water heater and the check valve/BFP. If a tank is existing and has the incorrect pre-charge air pressure, the cold water pressure must be relieved so the tank air pressure can be properly set. Thermal Expansion tanks will prolong the life of water heaters as they absorb the excess volume created by thermal expansion. Backflow prevention is primary to keeping our water supplies safe from cross connection contamination. This technology has created the need for domestic thermal expansion devices that are here to stay.
Thanks and we’ll see you in the next article!
Sincerely,
Rich Grimes
We are back with another article and this time we will look at water quality and its effect on water heaters and boilers. BOILERS Boilers are typically closed loop systems where fresh water is used to fill the system but the same fluid is used over and over again. After a system fill, very small Read more
We are back with another article and this time we will look at water quality and its effect on water heaters and boilers.
BOILERS
Boilers are typically closed loop systems where fresh water is used to fill the system but the same fluid is used over and over again. After a system fill, very small amounts of fresh water will enter to maintain system pressure. Chemicals are added to inhibit corrosion and prevent freezing. The dissolved oxygen, calcium and other minerals will precipitate or “fall out” of the heating fluid. They only become present if fresh water is allowed to re-enter the closed loop system.
For instance, I experienced a scaled up heat exchanger on a properly installed closed loop boiler. After further inspection of the closed loop fluid it was found to be untreated fresh water. The maintenance crew had been using a boiler drain valve to extract heating hot water for cleaning purposes. This occurred every day where they would fill a 5-gallon bucket twice a day. They had access to a Domestic water heating system (right next to the boiler) that resolved their boiler scaling issue.
WATER HEATERS
Water heaters are designed to heat volumes of fresh water up to temperature for domestic and potable uses. The fresh water can contain various minerals and chemicals that will shorten heater life or cause adverse conditions when heated.
Scale build-up is the single most cause of water heater failure and loss of efficiency. The nature of water heater design can be a definitive factor in longevity and overall efficiency but the water conditions are area, utility or site specific. Calcium is present in water and it wants to stick to heating surfaces as it changes from suspension to solids.
ANODE ROD PROTECTION
Most tank-type water heaters use a ceramic porcelain Glass lining to protect the steel vessel interior from fresh water. The glass lining requires a sacrificial anode to cover and protect any weak spots on the lining. Electrolysis will attack the weakest spot on the lined tank interior and the anode is designed to give itself up to fill that particular spot. Over the life of the heater the anode will sacrifice or “give up” small amounts of its soft metal to protect the lining.
The two metals most commonly used in water heaters for anodes are either Magnesium or Aluminum. These metals are softer than steel and less noble. They can sacrifice themselves prematurely if attacked by the content of the water. These have distinct signs and smells that help to recognize how to deal with such issues.
Here are some common water problems related to water heaters and anode rods:
Hydrogen Sulfide – reaction created by a sulfate-reducing bacteria. It occurs with water that has high sulfur content and it attacks the magnesium anode. It is referred to as “Rotten Egg” smell. Hydrogen Sulfide gas in large quantities can be toxic and explosive.
Hydrogen Sulfide normally can be corrected by changing to an aluminum anode rod after performing a complete chlorination and flush of the tank and piping to kill the bacteria. Some manufacturers specifically use an aluminum anode rod as standard equipment in Florida to avoid the reaction to magnesium.
Aluminum Hydroxide – reaction caused by high pH water. It occurs many times in areas with high chlorine/chloramines in the water supply. Chlorine has a very high pH of 11.7. This reaction forms a jelly-like substance on the anode rod and in the bottom of the tank. It can appear as grey, blue or green beads or gel. The odor produced smells something like week-old trash so it is not something you can tolerate very long!
High pH also means alkaline or scaling so the tank must be flushed out and possibly de-scaled. The reaction is treated with the other viable anode made of magnesium.
Water Softeners – water softeners reduce grains of hardness through a process of ion exchange. Most water softeners exchange sodium (salt) ions with insoluble calcium and magnesium ions. Sodium can increase electrical conductivity and accelerate anode consumption. Use of water softeners warrant monitoring of pH level, conductivity and anode inspection at a regular interval, no less than once a year.
Stagnation – allowing the same water to exist in the tank for long periods of time will result in stagnation. The potential for bacteria increases. This can attack the anode and the results are smelly water and a heater that needs service. Many seasonal residents of Florida will leave their winter homes and forget to drain down their water heater. They typically turn off the power before they leave and the low temperature, stagnated water starts creating the perfect Petri dish. The other application is a larger storage heater that does not get used much, where very little fresh water enters to replenish the stagnated water. A 50 gallon heater on a break room sink is a great example of an over-sized and under-used heater.
Grounding – bad earth grounding can create an electrical potential that will erode the anode at a rapid rate. Once the anode is gone, the steel tank is attacked by the electrolysis.
NEW ANODE TECHNOLOGY
There is newer technology on water heaters for cathodic protection. Electronic controls can help to implement a non-sacrificial anode. The benefits of such a device are a milestone in tank protection.
The Powered Anode is a titanium rod that is immersed in the top of the heater tank. It can function as a Low Water Cut Off to insure that the tank is full of water. Titanium is a very hard metal, mostly impervious to fresh water and much more noble than steel. It will last longer than the water heater and does not sacrifice itself. So there is no smell that will be generated by this non-sacrificial anode rod.
The electronic controller will send out a micro-DC current to the Titanium rod to offset electrolysis. The electronic controller sends out more micro-DC voltage as the tank lining gets older. At some point, the electronic control cannot put out any more current. The integrity of the tank lining is so diminished it is already leaking or within days or weeks of leaking. This is a valuable feature, to know that when you cannot maintain power to the electronic anode rod, you are about to experience a tank failure in the very near future. Time to schedule a change out!
OTHER WATER ISSUES
Water can and will contain a variety of chemicals and minerals that can create adverse conditions when heated. The heating of the water will increase precipitation of scale. It causes the calcium to leave solution form and become a solid that sticks to itself and accumulates on heating surfaces.
High iron content is very common in Florida with well systems. Tannic acids will turn the water yellow to brown in color. Lime is naturally present in every water source to some degree. Bacteria can also be thriving in a particular water supply. The process of heating accelerates the various reactions. There is a wide range of targeted treatment and filtration products that can address these such as UV, Iron filters and the like.
It is important to remember that it is not the fault of the water heater, but a adverse reaction to the water…