Saving energy, energy savings and recycling heat
We'll list, then ignore, the forms of energy we're not using in this project.
We're not using wind or solar (because we haven't seen any products that can go 40 years without requiring a significant amount of maintenance, repair or replacement), and anyway, this is about using less energy, not about going off the grid. We're not using wood or coal because they, too, involve their own clusters of chores. We did, after much consideration, decide against geothermal, based in part on concerns over the exchange field long-term durability and in part on the ways that other measures we plan end up reducing the balance sheet on benefits from geothermal. We're also not using propane, but in this case it's because a near equivalent, natural gas, is available.
Just two fuels: natural gas and electricity
One excellent reason for confining ourselves to these two fuels is that together, they allow access to the broadest spectrum of existing products. Between the two, natural gas offers the better cost efficiency so, for the most part, when and where we have a choice, we choose gas.
The first time through this section you'll probably want to read it top-to-bottom; when you come back later you may want to jump instead of scroll, so here ‘s a list of jump locations on this page:
Electric lighting is powered lighting, but it's not the only source of lighting in a house.
There's also ambient lighting, primarily through windows.
We could sit fat and happy by just installing LED fixtures (50,000 to 100,000 hour life expectancy) everywhere we need a light and save a lot of energy (and money) compared to traditional lighting. That would still be wasteful.
So one challenge is to be able to identify where people are, where they aren't and where they're going, so we never leave the lights on in empty rooms (but never turn the lights off on a room that isn't empty) and so that a person's path and destination will both be appropriately lighted.
And “appropriately lighted” reflects both the presence of a person and other factors: how much light is coming in the window, how much light is necessary for the observed activities and so on.
This means the ability to sense the presence of people in every room and passageway, the ability to read the existing light level in each of those and some clever analytics in the controller software to figure out what's up.
The cost of delivering hot water in this house gets cut several times over.
The first is in the choice of natural gas.
The second is in the choice of a tankless (“just in time”) hot water heater that isn't tasked with keeping a big tank of water at temperature 24/7. The third is a special class of those called a condensing tankless hot water heater, where the incoming cool water feed gets routed past the flue so otherwise wasted exhaust heat can preheat the water before it hits the heat exchanger - but wait, there's more.
Our builder, Don Cerra, is brilliant about these things and he suggested adding an indoor water holding tank. Water comes out of the ground in the 50s (Fahrenheit) and the attic space in this house is maintained at very nearly room temperature. With a 200-gallon tank in the attic, we get a 15-20 degree rise in temperature for essentially free, meaning that much less fuel to burn to bring the water up to a 100-105 degree (for example) delivery temperature.
We're also using an EcoDrain heat exchanger at the drain pipe of the shower; draining hot shower water heats the exchanger and the exchanger heats the water running from the holding tank to the water heater (the two water flows never intermingle) - yes, it recycles heat.
Note that there are chains of consequence throughout the house and some of them touch here.
Keeping a condensing tankless hot water heater maintenance free for 40 years can be iffy - few will actually last that long - in part because of something that ages them prematurely - and that's preventable: scale in the water. Scale in the water also accounts for crud in the shower heads and early repair or replacement of many items in a home's plumbing chain. A whole-house water treatment solution designed to address the condition of the source water and tailored to totally eliminate scale reaps benefits across the system.
Another secondary effect is in the extreme acidity of the acid drip condensate that emerges from several kinds of equipment, including this type of hot water heater and many HVAC units; we plan to address that with a purpose-built neutralizer.
The water pipes also play a role. Wherever we can use 3/8” pipe instead of 1/2” pipe, we reduce the amount of water in the pipes; for a 50-foot run it's a reduction from 0.46 gallons to 0.32 gallons; purging standing water from that 50-foot line to deliver hot to a tap happens twice as fast with the thinner line. By using insulated PEX pipe, hot and cold water in their respective pipes retain their temperature longer - hot stays hotter and cold stays colder - and each has much-reduced impact on the temperature of the space around them, a small but sweet plus for HVAC.
Heating, cooling and ventilation planning also involves layers of interconnected selections.
The nature of the floor plan of the house connects it to both the 3-car garage and the bonus room over that garage through a breezeway; our approach had to involve two HVAC needs - one for the main house and one for the garage/bonus room combo.
To help reduce noise, we decided on a ducted system using dual-wall insulated ducting with an antimicrobial coating. In addition to reducing noise, this means less heating/cooling loss for air in transit.
The ducting connections are wrapped with foil tape to prevent leaks and most of the ducting run is buried in closed-cell insulating foam.
Then we decided that we need to reinvent the thermostat. Our automation will make about 2,000 temperature measurements ten times per second, plus sensors in about a hundred places to monitor humidity, barometric pressure and ambient light. 30 of our controllers (each a tiny computer) analyze those readings and send distilled readings to a supervisor controller for the comfort control systems. That distilled data also identifies the position of every warm body in the house, which is a key to identifying occupancy versus vacancy (for heating, for lighting and for other purposes).
We can fib to the thermostat, productively, by analyzing the immediate conditions in the house and determining what thermostat setting would allow the most overall comfort for the least energy and best system longevity. Modulating vent registers play a major role in this, too.
Our controllers let us also include ceiling fans and the fireplace as active participants of that same comfort system.
And we should mention that in the event of a fire, the controllers turn off every fan and every blower and close off the vent registers because any kind of air flow can help a fire grow.
The act of cooking itself does not stand alone; food has to be preserved with refrigeration, dishes need washing and so on.
So in the kitchen we can bring few new tricks to the metaphorical table. We can choose “column” style (separates, like built-ins) for the refrigerator and freezer because combination tend to create compromises in both refrigerator and freezer roles while separates evade those.
For the dishwasher, there are many new choices with great energy efficiency and low noise. The garbage disposer needs to also place a priority on low noise as well as on jamming as infrequently as the state of engineering will allow. Specific choices in gas and electric (including microwave and convection) cooking have more to do with convenience than energy differences since the most efficient gear also tends to be much better built.
In a modestly populated residence, the total number of hours spent cooking during a year represents a fairly small energy footprint and the biggest energy reductions we can achieve happen by choosing gas appliances for major roles.
Our investigations into laundry equipment are incomplete, but we do know that appropriately sized HE washers are already making significant energy reduction contributions through improvements in their efficiency. We believe that gas dryers will bring the usual benefits associated with the fuel but we still have to look into efficiency improvements among electric models to see if that benefit has dwindled.
We don't know for certain that the property will end up having a pool, so we have not examined the state in the art in support equipment, but we did learn one trick. With steel roofing that provides an air gap between the bottom of the metal roofing panels and the radiant-reflective wrap over the roofing boards, we've been told that a run of cold water into a pex (plastic for plumbing) pipe between the steel and the foil provides a good source of hot water for heating the pool with nothing bu the sun doing the heating.
The biggest energy savings happen when you can avoid needing it in the first place.
Our plans include many measures for separating the environment inside the house from the environment outdoors, and for assuring that where and when we do shuttle temperature changes around the house, we take steps to assure they will arrive with full or nearly full potency.
The crawl space under the house uses insulated concrete forms, meaning layers of insulating foam on both sides of the poured concrete. The exterior walls of the house are structural insulated panels, a sandwich of engineered wood around a complete core of insulating foam. Spray closed-cell polyurethane insulating foam goes in the flooring, ceiling and attic spaces.
A metal roof inches above the roofing board and a thermally reflective (“radiant”) foil atop the roof board isolate the attic from the outdoors. Double-wall ductwork insulated HVAC runs. Extra-thick exterior doors with insulating foam cores play a role. Form-fitted insulated backing on the exterior siding adds a bit. And the windows everywhere are multiple-pane energy-tuned structures in frames that deliberately break the heat conduction path between the outside of the window frame and its inside.
By separating the indoors from the outdoors, we dramatically reduce how much energy it takes to maintain a comfortable indoor space.
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