The more efficient homes become, the more "tighter" they become. I wouldn't recommend a standard chimney vent water heater as they burn inside air. I'm pretty sure they make direct vent tank water heaters, but they arent very common so a tankless would be a great option as models are available that burn outside air and they are 95% efficient (condensing).
Seems like a logical problem. The water between point a and b is obviously sitting in the water distribution piping in the home and will eventually be room temperature. That problem could be solved with a recirculating line, or if you have a laundry room sink next to the washer a conscious homeowner could just run that until the water gets hot.
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In Germany it really depends on the design of the house. Most of the homes have central heating fired by natural gas, heating oil or wood pellets. In those case there typically is a central boiler. In order to kill bacteria - in particular the species legionella - the water temperature is kept above 55°C (131 °F). My home, which was built in 1982, has a central heating.
But there are also many appartments where warm water is heated with tankless heaters. There can be one tankless heater for the whole appartment, or there can be separate tankless heaters, one for each bathroom and one for the kitchen. Decentral tankless heaters mostly use electricity. A central tankless heater for the entire appartment can be used for both heating and warm water. In this case it is usually fired with natural gas.
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This is considered a cross connection and cannot be done legally. Unless: you are using the heating water to heat a storage tank full of domestic hot water or you use the one (that i'm aware of) available tankless heater with separate heat exchangers made by navien.
I have worked and researched quite a bit since I started this thread and thought I would report on what I've come up with. I'm providing an overview as opposed to details.
1. Use of Steel SIPs doesn't seem to be feasible in Lubbock TX. No one local who has experience. Closest installer is about 2 hours away and I just don't want to deal with that. I can't go look the installer in the face any time I want to discuss things. I am leaning heavily towards a steel structure. However I'm still looking at alternatives.
2. Heating and cooling: Really interested in and planning for passive solar heating and cooling. Have a preliminary design that I came up with and need someone who understands and has personal experience with convection currents to review my design and provide feedback.
a. Use of solar chimney or double wall acting as a solar chimney on the north side of the house with outside vents to open for summer and close for winter. May use 2 solar chimneys; 1 for sleeping areas and 1 for living areas.
b. Air flow planning includes the basement. In the summer this will help cool the rest of the house. However, the challenge is to also heat the basement in the winter which will depend on the efficiency of the venting and heating of the air in the chimney to get the warmer air into the basement.
c. Proper location and use of vents is critical in the distribution of cooler air in the summer and warmer air in the winter. Use of fans should be minimized for all seasons.
d. Use of overhangs for south wall will be optimized for shading in the summer and full sun in the winter.
e. Not sure about this yet but thinking about including a sun room on the south side to supplement the heating.
f. Possibly use a wood burning stove to supplement passive heating. There are alternatives to a wood burning stove but bottom line is I won't be using a conventional fireplace which is a very inefficient means of providing heat.
3. Water heating and distribution: All wet areas of the house are in the same area to minimize the distance hot water needs to travel. Wet area for main floor is directly above the basement wet area. I am being steered away from tankless water heaters by people who have them in service or ones who've use them before. Regardless I'm still entertaining this solution. I just haven't done enough research yet. Also looking at solar water heating. Again, I haven't done enough research on water heating solutions to actually form an opinion.
4. Lighting: I would like to include passive lighting but haven't done much research on this yet. From what I've seen, I need to be sure whatever I do for passive lighting that it doesn't negatively impact the passive heating and cooling.
5. Waste Water: Separate plumbing for gray and black water. Using gray water for garden irrigation decreases the amount of waste going into the cesspool. More research necessary.
6. Rain Water collection: More research necessary. We don't get a lot of rain in west Texas so this isn't anything critical but want to include it as a research item. I know there are some states where it's illegal to collect rain water. Reading about that I can see both sides of the argument but good grief. Seems to be going a bit too far. If rain falls on my property and I own the water rights, then it's mine to do whatever I want to do with it. Don't mean to start a debate. Just a random off topic thought.
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I spent years researching all this stuff, then years building an energy efficient house here in Japan. I am quite dialed in on this topic.
I researched every possible kind of structure and insulation, cost benefit ratios, etc. In the end I concluded that a standard stick-framed structure with high-density fiberglass infill, unfaced, between the studs, and wrapped on the outside with 1.5 inches of foil backed polyurethane offered the best bang for the buck. With cement fiber rain screen siding and a cold roof (galvalume metal). And also very tightly sealed with a lot of caulk even in the framing and tight windows.
The roof, of course, has a lot more insulation, and that is the low-hanging fruit of energy efficiency. Insulate the roof!
As for mechanical systems, here in Japan tankless has been the norm until recently, but nowadays people are installing off-peak heat pump systems. These heat pumps run off the cheaper night-time energy. It costs about 5 c per kilowatt vs 30 for daytime. Every market is different, but in my market, off-peak electricity is the cheapest source of energy.
Some people also install cogeneration equipment, which heats water and also generates electricity. The product is made by Honda, and is also known as Micro-CHP. Runs on natural gas. That may also be a very efficient, but it seems overly complicated.
In real life, where my house falls down on efficiency is in terms of windows. We reached the best compromise on price and performance for the windows, but given that the design has so much glass in it, there was inevitably going to be a great loss in performance due to windows and sklights.
But we wanted the glass to have lots of light and to have great lake views, and we are perfectly satisfied in that aspect.
As for building in Texas. I don't think you have a big earthquake problem, and I don't know if hurricanes are much of a problem inland, so I wonder if you need the structural strength benefits of a steel or concrete structure. Here in Japan, these kinds of structures cost 30 to 50% more than wood. And they do have drawbacks. From my POV, the only payback of steel here is that it allows you to build taller structures on urban lots where land is expensive. Code only allows wooden structures of 3 stories here, but you can build as tall as you want with steel.
I think the energy saving with steel is in terms of embodied energy. That is, once the steel is produced, it can always be melted down easily and recycled into other products. So there is an overall energy benefit in terms of sustainability, perhaps. Aluminum structure is even more so, but aluminum framing members are a lot more expensive.
As for concrete, I think it is very suitable for Texas. Please research the topic of ICFs. These give you an insulated, super efficient concrete house at a competitive price. And you can even DIY it. Your concrete structure must be insulated with lots of foam, in any case. Do not imagine living in a bare concrete house. It's unpleasant.
With ICFs or SIPs or foam insulation of any kind in a place like Texas you need to focus on getting a product that has termite treatment infused into the foam itself. Termites and carpenter ants like to eat the foam and also to make houses inside it, so you must be sure that it's the ant-proof stuff. R-Factor is one brand that comes to mind.
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