Concept

After you have a conceptual plan for your home, there are many energy questions to be answered, but two of the most important questions are:

1. How much energy will it take to heat your home?
2. How much energy will your solar resources provide?

It is by working through this step that you will know if you initial plan will meet you goals or not.

There are many software packages that may be right for your situation. Some of the products I use include: TREAT, RETScreen, Rem Rate, Manual J, and Energy-10. Each has its strengths and weaknesses and in the total design and analysis, each has it specific application.

Application

Question 1: For my situation, especially since I wanted to consider minimal heating of the overall space and higher heating levels for year-around comfort in the Active Area, TREAT was what I used to answer the first question – How much energy would this plan require? My TREAT modeling indicates that I will need about 24 million BTUs for heat. This is less than a third of what is needed for a similar code built house. I also know this estimate is high because TREAT does not handle several of my design details well, so I estimated the “real” heat demand would be very close to 22 million BTUs annually. Plus, I will need another 250,000 BTUs for domestic hot water, for a total of 22.3 mmBTUs

Question 2: I have space for and plan to have up to ten 4x8’ flat plat collectors. How many BTUs will these collectors deliver? There are several packages that help with the complex task of calculating how many BTUs a specific set of collectors will deliver. The many variables include, primarily: manufacturer, model, tilt, orientation, and operating parameters. I chose RetScreen for two reasons; first, Ben Nusz,(link to Project Contractor page and come back to here??) the water heating expert, recommended it and gave me an on-line tutorial; and second, its development was coordinated by the Canadian government (it has to be good; its cold up there) and it is distributed for free! This is a great software product for a wide range of renewable energy projects and it worked well for mine. After entering the various data, the answer is the ten collector panels will deliver over 18 million BTUs.

The result is the house will require 22.3 mmBTUs and the collectors will deliver 19.3 mmBTUs. Thus, I am 3 mmBTUs short and will need to burn about a face cord of hard wood through the heating season to make thermal ends meet. Being this close is an important step, but there is a detail remaining – timing. What is still needed is a way to capture sun heat and release it when needed. What is needed is “heat storage and regulation;” see Solar Thermal Storage and Solar Operations.

In addition to answering these key questions early to know if you are on the right track, there are several other interesting questions that can be answered with computer analysis, including:

How warm will the Active Area be? The short answer is, “as warm as I want to make it.” But what I want to understand is, “How little heat I can apply to keep it comfortable, and given its passive solar properties, “What will the temperature swings be without wood?” There are many factors to these questions. I am currently in the process of applying Energy-10 to the Active Area, treating it as an independent space. One of the difficulties is that while the back wall and ceiling are very well insulated, (they include our bedrooms) they are not R-1000. So, to calculate a practical answer will take some simplifying assumptions, and a unique application of the software, which I haven’t mastered quite yet. But the bottom line is, there will be enough energy to keep this space comfortable and any extra heat can be conserved by sending it to the “outlying” areas – our bedrooms.

How will the house rate, in terms of ENERGY STAR labeling? We used RemRate, the only tool capable and allowed for this purpose in the NYSERDA program. The answer is the house rates very high; it has a NY HERS Rating of 96.6. The lowest ENERGY STAR tier requires a score of 84, which is better than “code.” Tier 2 requires 87, and the highest tier, Tier 3, requires a modest 89. So, 96.6 is pretty good indeed. And the good news is that there are several features of my house design that REM Rate does not consider, so my scores should be a bit higher!

The final question, in which I will soon be interested, is: How many BTUs will it take to warm the bathrooms each morning? This is best answered by using software supporting the HVAC industry standard, Manual J, to calculate each room’s heating load. I will work this out before I make my final decision on just how large the heat storing water tank should be.

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