[jeff5may]

Now that a site survey has been performed, we have a clue as to the condition of the home, the heating and cooling loads, and any issues with the home. Now we can begin to put a plan together.

Take out your site survey and energy audit from the previous step. Look up your existing heat loss and load at the home's design temperature. This will serve as a baseline for consideration of options. With these figures, it becomes easy to compare heating and cooling systems and their relative cost vs. efficiency ratios.

Now is the time to decide whether to improve the existing structure or not, and how much. Take note of any recommendations in the energy audit and decide what to do or not to do. Estimate the cost and time frames of improvements and write them down. Depending on the home, this work may end up costing more than the HVAC work, but that's OK. This type of improvement has the potential to drastically alter the way your home feels and acts when the weather gets nasty. If the work drastically reduces your energy needs, you may not even need to upgrade your HVAC system in the end.

If it was decided to improve the structure, write down new heating and cooling load estimates for the modified structure. Use these figures for the lower limit of capacity for your heat pump system. If you figured correctly, a system sized to meet these needs will perform well for 98 to 99 percent of the year. For most, that's the best you can do economically. For those 5 or less awful days a year, the system should fight hard to keep up, running constantly. The temperature may deviate from the desired setpoint for a while if the system loses ground against mother nature. You need to decide if this is acceptable or not.

If it was decided that the Comfort Control system must cover 99.99 percent of the load, the heating or cooling side will most likely need a backup source. In most every home, there will be a particular area that suffers the most during extreme weather. This area tends to affect the rest of the home. If the area cannot be modified or isolated to avoid the effect, the backup source should pour its energy into this area. For heating, a natural gas unit or a single-zone, sub-zero rated mini-split is most cost effective. For cooling, a window air conditioner or mini-split unit can be installed to serve the extreme needs of the area. This backup source may be oversized to eliminate all doubt. Since it will only run in a temporary fashion, the most efficient design is usually overkill, as it will be much more expensive than a run-of-the-mill source, and not save that much energy overall.

That being said, every home is different, so a creative solution may be effective and viable. Many ecorenovators have devised simple mods to their existing systems to improve performance. It may be possible to eke out a few extra percent of efficiency that allows the system to cover temporary peak loads. This option may reap great savings or may not be possible at all.

After settling on design goals for the system, you may now begin to compare equipment. If you did your homework up to now, choosing equipment will be simple. Deciding which way to go is an exercise in personal preference and overall system goals as well as pricing. Reputable manufacturers publish all the data that you will need to determine suitability of their units in whatever conditions you may need to cover. They also publish tons of pictures of their units in various settings and describe the operating behavior and what makes their units unique. Some hype is always included, but if you do a fair amount of shopping around the hype will become obvious.

Once you have chosen equipment, you can assemble a system blueprint and assign dollar values for equipment and labor. If much of the work will be performed by contract labor, you can submit this plan to contract firms and begin to consider estimates for the job. If much of the work will be DIY, it is recommended to seek estimates anyway. This way, a professional can critique your plan and suggest other options you may or may not have considered. The pro may discover problems with the plan that cannot be ignored. If no estimates are requested, at least have a professional building inspector or engineer review your plan. The value of having your plan checked before the fact far outweighs its cost.