When your furnace goes out, having it immediately replaced may seem like a foregone conclusion, but some homeowners would do well to consider the current condition of their home and the long-term possibilities—not to mention a weather forecast—before plopping down $10,000 or more on a new furnace. It may sound crazy, and you certainly don’t want to make your home improvement decisions based on the groundhog’s shadow, but taking unusual steps to get through the last blast of winter may pay off in the end. The advantages of waiting until spring to install a new furnace or heating system are pretty straightforward, but they’re also frequently underestimated. The cost of installing a furnace in the middle of winter is higher than needs be simply because HVAC companies have to pay employees overtime to keep pace with the surge of furnace repairs and replacement. Meanwhile, manufacturers have cut prices due to the current recession, creating a perfect storm for homeowners to complete installation of a high-quality heating system at a reasonable cost.

In fact, more than an evaluation of the eventual benefits, the logistics of riding out the remaining weeks of winter without central heating will likely determine the relative wisdom of this choice.small marine ac units You can’t just say, “It’s March 3rd, it’s supposed to warm for the next few days, I’ll be fine.” how much is a new 5 ton ac unitSpace heaters will almost surely be part of your plan to survive without central heating, but you’ll need to make sure you’re using an extension cord with a sufficient load-bearing capacity. what is a 2 ton ac unitNor can you simply drag a space heater around the house with you: If you don’t have properly insulated plumbing, your pipes can freeze and burst. Of course, this is something that might need to be done whether your heating is working or not.

If the temperature gets too cold, you may need to shut off the water and find some place to stay for the night. Yet, one or two nights at a cheap hotel may be well worth it on the back end, and you can treat it like a miniature get-away for you and your family. If you’re going to take this road, then there should probably be a prize at the end of it. A standard, reliable furnace doesn’t need to take weeks to find and install. Investing that something extra, however, can take a bit more work. For homeowners looking to make an investment in their home and promote sustainable living, the question isn’t whether to go green, but how green to go? A new gas furnace with an Annual Fuel Use Efficiency rating of 95 or higher might cost an extra $2,000 or $4,000. An air-source heat pump system might cost an extra $3,000 or $6,000. Truly, renewable heating solutions, like geothermal heat pumps and photovoltaic energy systems might cost an additional $10,000-$20,000, but these systems also enable homeowners to receive tax credits of $2,000 or more.

Thus, even after these tax breaks, you’re probably still going to be paying more than a run-of-the-mill heating system, but if you wait till spring and take advantage of these tax credits, lower utility bills can recoup the extra expense in just a few years instead of the standard 10-20 years. Need to find a pro for your furnace repair? This past fall homeowners started looking at these renewable technologies as legitimate and cost-effective heating solutions. From the fall of 2007 to fall 2008, geothermal heating system requests more than quadrupled, while photovoltaic system requests increased almost 20-fold, according to HomeAdvisor, leading online resource connecting homeowners to home improvement contractors. Meanwhile, the number of requests for high-efficiency, air-source heat pumps—a more established heating system—still doubled from 2007 to 2008. Waiting to replace your heating unit may seem like a nifty, if daunting, idea for many people. You want a great deal on a new heating system, but is it safe?

Fortunately, you have a built-in professional resource to help you out. Except in rare cases of catastrophic failure, few homeowners decide to simply chuck their furnace without calling a HVAC contractor. When this contractor is diagnosing the problem, have him or her evaluate your home and its ability to safely withstand the last few weeks of winter. Be upfront with your contractor about the situation. Not only will you get professional advice about surviving the rest of winter without central heating, but this will allow you to conduct preliminary interviews for honest, reliable contractors to eventually install your new heating system. You can be the first to comment! The Z transform is a means to mathematically describe a sampled data system. The Z transform is given by the following equation: z-n is a delay operator, n is the number of previous unit delays, T is the sampling interval, and V(nT) are the discrete analog samples. This equation cannot be represented directly in MC5.

MC5 can run its equivalent Laplace transform though. With a Laplace function source, any z domain transfer functions may be converted to a Laplace transfer function through the substitution: One of the common uses of z transforms is to simulate discrete-time systems such as digital and switched capacitor filters. The following example is adapted from an article by B. Al-Hashimi and M. Moniri in the April 11, 1996 edition of EDN titled "Spice provides z-domain circuit simulation." This example simulates a third order, elliptic, lowpass switched-capacitor filter. This filter is represented by the following z domain transfer function. The figure below displays the MC5 equivalent circuit. The circuit contains two components. One is the SPICE independent source, V, that provides the input stimulus, and the other is a Laplace function VofV source which represents the switched capacitor filter. The V source is defined as a 1ms pulse with 10ns rise and fall times and a 2ms period for transient analysis.

For AC analysis, it is defined as an AC small signal source of magnitude 1V. The Laplace source's Laplace attribute is given the name ZFILTER. ZFILTER is defined through the following five .define statements. In the above define statements, FC is the clock frequency value whose reciprocal is the sampling interval, T1. T is not used as the variable in this case due to a conflict with the time variable, T. ZT is defined as the Laplace equivalent of z, and Z2T is defined as the Laplace equivalent of z*z. Finally, the transfer function is included in the define statement for ZFILTER. The + on the second line of the ZFILTER define statement is a continuation character and has no effect on the equation. The figure below displays the transient results of this circuit. The transient analysis clearly shows a sampling interval of 41.6us. Using Transmission Lines as the Z Domain Delay Element A second method for simulating a Z domain transfer function is to implement the 1/z terms with ideal transmission lines.

The transmission line equivalent of 1/z appears in the figure below. The transmission line is specified by its characteristic impedance, ZO, and its propagation delay time, TD. The TD parameter represents the sampling interval of the digital filter. The value of the characteristic impedance is not important as long as the line is terminated by a resistor of equal value. The source at the input of the transmission line is just a VofV dependent source with a gain of 1. This is just a buffer to isolate the 1/z elements when they are placed in series. To demonstrate the use of the transmission line for Z domain analysis, we will analyze a third order Butterworth digital filter. The transfer function for the digital filter is as follows: Below is the corresponding block diagram. With the use of transmission lines, the block diagram becomes an easier tool to design from rather than the transfer function. This diagram was created using Micro-Cap's graphic elements. The block diagram above is simulated by the circuit below.

The input to the filter is again a 1ms pulse in transient analysis and a 1V AC small signal source in AC analysis. For each 1/z element, one of the transmission line blocks has been placed in the circuit. Going from left to right, these produce the 1/z, 1/z*z, and 1/z*z*z delays. Each transmission line has ZO defined as 100 ohms, with a corresponding 100 ohm resistor terminating the line. The TD parameter of the transmission lines has been defined in order to give the filter a 20kHz sampling frequency. The other two elements in the filter are EVofV SPICE dependent sources. These represent the two sum nodes that appear in the block diagram. These two sources sum all of the elements specified by the block diagram together by using the POLY operator. The POLY operator performs the following function: POLY(4) 8 0 0 1 0 3 0 5 0 1 -1.081 .607 -.123 SUM1 defines the sum at the input, and SUM2 defines the sum at the output. For a typical transfer function such as: the POLY sources would be defined as: