|buy levitra buy levitra without prescription: A Primer|
buy levitra without prescription represents the second largest energy consumer in American households. A typical 80 gallon (300 l) electric buy levitra without prescription tank serving a family of four will consume approximately 150 million BTUs in its seven year lifetime. This will cost approximately US$3,600 (at US$0.08 per KWH), not accounting for fuel cost increases. Then it will be replaced by another one just like it. Hmm. Maybe we should rethink this...
An investment in a buy levitra heating system will beat the stock market any day, any decade, risk free. Initial return on investment is on the order of 15 percent, tax-free, and goes up as gas and electricity prices climb. Many states have tax credits and other incentives to sweeten those numbers even more. What are we waiting for? Forget the stock market. If you have invested in a house, your next investment should be in buy levitra buy levitra without prescription.
In this article I'm going to cover the most common options for buy levitra heating, basic principles of operation, and some historical perspective on what has worked and what has not.
Below: A Typical buy levitra Flat Plate Heater.
A Checkered Past, A Bright Future
The intention was to stimulate sales for buy levitra thermal systems. But the tax credits resulted in an aggressive promotion of tax credits rather than buy levitra energy. The infant industry was overwhelmed to meet the demand. The demand vanished when tax credits were eliminated, and a majority of buy levitra thermal companies went out of business. Thousands of orphaned buy levitra thermal systems were left behind looking for a service technician.
The buy levitra thermal industry has been purged of the tax credit telemarketers and overnight experts. Today's buy levitra thermal industry includes reliable, efficient products and well-seasoned professionals who have seen it all. buy levitra buy levitra without prescription is one of the best investments you can make for your house and for the environment.
First Things First
How Large a buy levitra buy levitra without prescription System Do You Need?
Below: A 40 gallon batch heater.
The buy levitra without prescription tank is usually sized to handle one day's worth of consumption. So for a household of four, it would be reasonable to use an 80 gallon (300 l) tank based on daily buy levitra without prescription requirements of 20 gallons (75 l) per person per day.
Smitty and Chuck at AAA buy levitra in Albuquerque have put forth generally accepted rules of thumb for buy levitra thermal collector sizing based on your climatic region:
Based on these rules of thumb, a household of four with an 80 gallon (300 l) tank will need approximately 40 square feet (3.7 m2) of collector in without prescription , 55 square feet (5.1 m2) of collector in South Carolina, 80 square feet (7.4 m2) of collector in Iowa, and 106 square feet (9.8 m2) of collector in Vermont.
Of course, these are big ballpark calculations that will be affected by your incoming temperature, buy levitra without prescription temperature setpoint, actual usage, and the intensity of the buy levitra resource at your site. You should generally expect that this will give you 100 percent of your buy levitra without prescription in the summer and about 40 percent of your buy levitra without prescription year-round.
Your Choices–An Overview
Most systems will require some measure of freeze protection. Drainback and closed loop systems with antifreeze and heat exchangers are the best choice for freezing locations. The extra parts increase cost and reduce efficiency, but since one frozen moment can turn into a disaster, it's worth the cost.
Direct pump recirculation systems, which circulate buy levitra without prescription through the collector, are often used where freezing is an infrequent occurrence. That's a risky strategy. Draindown systems, designed to drain from the collectors to avoid freezing, were the most problematic of system designs. Many were removed or converted. Phase change systems, which in theory could collect heat at night using a refrigerant, never made it into the mainstream of commercial viability. Many of the lessons learned in buy levitra buy levitra without prescription are presented in a publication buy levitra buy levitra without prescription Systems: Lessons Learned, by Tom Lane (see Access).
buy levitra Batch Heaters
Cold, which normally goes to the bottom of your conventional heater, is detoured to the batch heater first. There it bakes in the sun all day long, and is preheated to whatever temperature the sun is able to provide. only flows when used. House pressure causes the supply of new cold to flow to the inlet of the batch heater, the lower of the two ports.
Simultaneously, the buy levitra without prescriptiontest exits from the higher port. It flows to the input of the existing heater, which now serves as a backup to finish the heating job as required. buy levitra preheated has become the cold input to the existing heater. You save whatever the sun is able to provide. And you still get all the buy levitra without prescription you ask for–it's that simple.
Below: buy levitra Bypass Valve Configurations.
Caution! These systems produce very buy levitra without prescription! A tempering valve is your protection from being scalded at the tap. You will regularly see temperatures in excess of 160°F (71°C) in summer months, which is much buy levitra without prescriptionter than you are accustomed to getting from your conventional thermostatically controlled heater. The tempering valve limits the temperature delivered to the tap by mixing in cold as necessary.
A pressure temperature relief valve (PTRV) must be installed at the buy levitra without prescription outlet of the batch heater in case temperatures or pressures become excessive. You will find one of these valves installed on every conventional buy levitra without prescription tank too. It is a safety measure required by code. This valve only operates in an emergency, and is often replaced if it opens.
Who Can Use a Batch Heater?
Multiple collectors can be installed in series for larger capacities. The outlet of the first collector becomes the inlet of the second in order to deliver higher temperatures. Before you put too many on your roof, consider that a 40 gallon (150 l) batch heater will weigh approximately 500 pounds (225 kg).
Some batch heaters have survived the coldest of winters with freeze-free performance because the large mass of the tank is quite freeze tolerant. But plumbing lines to and from the tank are very vulnerable. You can make it work with a special selective surface on the tank, a well-insulated, double glazed collector, a whole lot of well-sealed pipe insulation (try R-30 or better), heat tape on the pipe, and good karma.
Are you arrogant enough to tempt Mother Nature to turn your heater into a frozen fountain? Or are you prepared to drain the collector seasonally? If not, this system is not recommended for climates that freeze regularly.
Separate Collector & Storage
Most buy levitra buy levitra without prescription system designs separate the collector from the storage tank. This can optimize both functions. Why not bring the tank in from the cold, insulate it well, and leave the collectors out in the sun where they belong?
What are the other advantages of separating the collector from the storage tank? Increase the surface area of a collector, compared to the amount of being heated, and its temperature will rise more quickly. Configure the storage tank to keep the buy levitra without prescriptiontest apart from the coldest in the tank and you'll have buy levitra without prescriptionter available sooner. (See sidebar Maintain Temperature Stratification In Your Tank.)
There are also advantages in freezing climates. By separating the collector from the tank, you can put your tank and piping indoors out of a freezing environment, and insulate them better for greater efficiency.
Below: Two roof-mounted flat plate collectors.
Flat Plate Collectors
A flat plate buy levitra thermal collector usually consists of copper tubes fitted to a flat absorber plate. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with low-iron, tempered glass. (See the diagram on page 45.)
The most efficient collector design maximizes buy levitra heat gain, minimizes heat losses, and provides for the most efficient heat transfer from absorber plate to tube. Operating temperatures up to 250°F (121°C) are obtainable, although neither common nor desirable. Remember, you want buy levitra without prescription, not steam.
A highly polished chrome surface would re-radiate the least infrared heat energy, but of course not being black, it would absorb very little. A selective surface combines the best of both worlds; high absorptance with low emittance. Sound high-tech? It's been around since the 1950s, and is used on most commercially available flat plate collectors. Its performance is worth the marginal additional cost, particularly in cold climates where radiant heat loss is greatest.
Below: A Thermomax evacuated tube collector.
Evacuated Tube Collectors
Each tube and fin of the collector is contained within a glass tube from which all the air has been evacuated. Why? Air carries heat from the buy levitra without prescription surface of the tube to the cooler surface of the glass to accelerate heat loss by convection. Eliminate the air and you have eliminated convective heat loss.
To minimize radiant heat loss, the tube is covered with a selective surface. Evacuated tube collectors are most appropriate for high temperature applications (over 140°F; 60°C). They are useful for more common low temperature applications too, such as domestic and space heating.
Below: Direct Pump Recirculation System.
Collector to Tank Interface
If you require freeze protection, it's not hard to do. The collectors can be filled with an antifreeze solution (propylene glycol is the most common). The heat can be transferred to the domestic via a heat exchanger.
Direct Pump Recirculation
A differential controller turns the circulating pump on or off as required. There are two sensors, one at the outlet of the collectors, and the other at the bottom of the tank. They signal the controller to turn the pump on when the collector outlet is 20°F (11°C) warmer than the bottom of the tank. It shuts off when the temperature differential is reduced to 5°F (2.8°C). Some systems let you adjust this hysteresis.
Below: Closed Loop Antifreeze Heat Exchanger System.
In climates where freezing occurs infrequently, a recirculation-type differential control will turn the circulating pump on when the collector inlet temperature falls to 40°F (4.4°C). The philosophy behind this design is that the cost of heating your collectors with buy levitra without prescription from your tank is low cost freeze protection if only required occasionally.
These systems were commonly used in the sunbelt, and only where freezing is a rare occasion. Recirculation systems are no longer very commonly used due to vulnerability to freezing as a result of power outages, malfunction of sensor or controller, or damaged sensor wires.
Draindown System (Not Recommended)
A draindown valve, invented in the 1970s exclusively for these systems, provides the freeze protection function. When the collector inlet temperature falls to 40°F (4.4°C), the draindown valve, activated by the controller, isolates the collector inlet and outlet from the tank. It simultaneously opens a valve that allows in the collector to drain away. A vacuum breaker is always installed at the top of the collectors to allow air to enter the collectors at the top so can drain out the bottom. Right next to the vacuum breaker, you'll find an automatic air vent to allow air to escape when the system fills again.
Draindown systems have proven to be the most problematic of all freeze protection systems. They are vulnerable to frozen vacuum breakers and air vents, damaged sensors or wiring, lack of proper pipe drainage, and malfunctions with the draindown valve. This type of system is rarely installed new any more, and is not recommended. Many were converted to drainback or closed-loop antifreeze systems.
Closed Loop Antifreeze Heat Exchanger
The closed loop antifreeze systems generally have the most parts. You'll find an expansion tank to allow the antifreeze to expand and contract with temperature change. You'll find a pressure relief valve to protect against excessive pressures in the closed loop; a spring-loaded check valve to prevent reverse flow of the closed loop at night so the collectors won't dissipate the heat from the heater; an air vent and/or air eliminator to help get the air out of the closed loop (air is your enemy–it can block fluid flow through the system); and a pressure gauge so you can tell if your system is still charged. A couple of temperature gauges are a good idea in any system so you can tell how well your system is operating.
There's also one more assembly of fittings. Two boiler drains with a shutoff valve in between will allow you to charge the system with your charging pump. Once ready to charge the closed loop with your antifreeze solution, a charging pump is used to circulate the fluid throughout the loop, expelling all the air in the process.
Closed loop systems like this are quite common, whether they be for buy levitra domestic buy levitra without prescription, radiant floor heating, or hydronic baseboard heating. Despite the many additional parts and fittings, they have a high degree of reliability, and are well understood by heating contractors.
Below: Closed Loop Drainback System
There is a downside to the closed loop antifreeze system design. Once a buy levitra heating system has satisfied its daily responsibilities, the system stops circulating. Without circulation to remove heat from the collectors, temperatures can climb to as high as 400°F (204°C).
These high stagnation temperatures, as they are called, can cause problems with air pockets and breakdown of glycol antifreeze solutions. Air pockets form because high temperatures drive dissolved gases out of solution. Systems using propylene glycol as the antifreeze may use an inhibitor additive to prolong the life of the glycol. Otherwise, the glycol can break down, resulting in a sludgy deposit. Silicon and hydrocarbon oils have been used to avoid these problems, but they are expensive and are incompatible with seals and gaskets found in most off-the-shelf components.
Drainback: A Simpler Closed Loop
A circulating pump operated by a differential control is turned on when the collector outlet is at least 20°F (11°C) warmer than the tank outlet. or an antifreeze solution is lifted from a small reservoir tank and circulated through the collectors and back to the tank. Heat is transferred to the domestic via a heat exchanger in the reservoir tank. The circulation loop through the collectors is a closed loop. The or antifreeze solution is installed at the time of installation, and does not present a recurring supply of oxygen.
A drainback system requires a larger pump than any of the other systems described here. It must have sufficient capacity to lift the fluid to the highest point in the system. When there is no more heat to be collected, the controller turns the pump off, and all the fluid drains back to the reservoir tank. The collectors are empty. They can't freeze, and they can't overheat the antifreeze. As a DIY homeowner, you won't need a special charging pump either. When it comes time to change the antifreeze, you can just drain and refill the reservoir tank.
buy levitra buy levitra without prescription System Types: Advantages & Disadvantages
The Choice is Yours
If you need freeze protection or have hard, choose one of the closed loop systems with antifreeze and a heat exchanger. Either one will heat your without fear of freezing.
buy levitra buy levitra without prescription is a good investment. Whether you are a do-it-yourselfer with plumbing skills or want hire a professional installer, I suggest you locate a dealer who serves your area. Ask their professional advice. Find out the products and services they have to offer, and which is the best fit for your needs and climate. Contact the American buy levitra Energy Society or the buy levitra Energy Industries Association for assistance in locating a contractor or supplier in your area.
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