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Q: I watched a presentation of yours a few weeks ago, the one sponsored by Sherborn and Holliston. Impressive and informative…many thanks.
As a result of the presentation I’m interested in adding 2” insulation board, as well as Aerogel, when I re-side the house. My wife does not like foam off-gassing, so we will leave our fiberglass batting alone and add the insulation board outside of it.
There are LOTS of insulation panel types to choose from. Any recommendations on which are best?
In your presentation you mentioned the aesthetic problem with adding 2” or 4” insulation boards, i.e. that they strand the window a few inches inside the siding. I wonder if this problem could be overcome by cutting the insulation board surrounding the windows into picture frame dimensions by making – a 3-d mitre cuts of the insulation at the window corners. One would end up with thin insulation board at the edge of the windows, but gain a lot of insulation everywhere else.
Any thoughts much appreciated.

A: You can certainly do this kind of mitre cut to lessen the impact of installing the insulation. If you are adding only 2” it might still look good. I think it is best to discuss this with the window installer. 
The Aerogel product has the best R value per inch at R10, so 1” has the same insulation as a 2” ISO board, but it’s only an inch deep. It is more expensive psf that ISO board. I do not know what it’s flammability rating is though. 
A more fire-proof alternative to adding the foam is to pull out the fiberglass and replace it with rockwool batts (Roxul comfortbatt is the most widely available). It is about R4 per inch vs R3 for fiberglass. Rock wool cannot burn (it is literally strands of melted rock) so it is better fireproofing. You can add a 1.5” rockwool board (R6) instead of the ISO board outside the studs too. If you are going to go to all this trouble it is probably worth adding an airtight/waterproof membrane on the outside too. Siga makes these type of specialized membranes. They have to be properly installed (with the seams sealed) to create the air-tight barrier. After this, your house will be far better insulated and far less drafty. 
I am glad your wife is concerned about off gassing, but I think their is an even bigger concern: fire resistance. Sometimes I feel like a lonely voice on the flammability of foam products. I intend to use rockwool when we add insulation on our rental property for precisely this reason. It is not just the flammability that bothers me, it is the thick black smoke created when foam insulation burns.I will also be adding the Siga membrane for air tightness too. 

The question I asked during the webinar was not very clear.  We have a water based heating system with radiators and a boiler fueled by gas.  We also have an air-sourced A/C system with small tubes running throughout the house (a UNICO, high velocity system) without the hanging of mini-split systems in each room.  Is there any way of using an air sourced heating system to heat the hot water in our radiator based heating system (either through the existing boiler or directly to the hot water circulation system)?

Hi Alan, yes is the short answer, you can connect an air-sourced heat pump to a water radiator system. These are sometimes called hydronic systems. But the long answer is a big more nuanced. These type of air-sourced heat-pump to hot-water systems are made by Jaga, Daiken and Spacepak and other manufacturers. I have never used one so I have no particular recommendations. The hot water in a boiler-driven radiator system is typically at 140F. Air-sourced heat pumps have a hard time getting the output side (whether it is air or water) above about 110F. So your radiators will no longer have that piping-hot feel (which may be good or bad – I have nearly burnt myself on hot-water radiators before). This means that it will take longer to heat your house up from cold – like when you come home from a winter vacation. But, as long as the heat output is matched to your heating load your rooms will stay warm, it will just take longer to get warm compared to what you are used to.

Are you thinking of using the UNICO high-velocity system with a heat pump so it would heat in the winter as well as give you AC in summer? We have a similar system in our rental house and I would consider replacing it with a heat pump if such a system exists. Let me know if you find one.

On Jul 1, 2020, at 2:29 PM, Chris wrote:I enjoyed the presentation & am looking forward to reading your book. I’m surprised air sealing wasn’t emphasized more. A new version of an old product looks very interesting: AeroBarrier. Instead of replacing 3 basement windows (12 x 32in); I’m getting quotes for Innerglass. Thanks!I haven’t yet read your pool topic & wonder if you’ve seen the pool heater that uses waste central AC heat?

Hi Chris, I am beefing up what I say about air sealing. I have seen houses where air sealing cut 25% off the energy bill. This was not true on my house, where my roof is a rubber membrane and my siding is tongue and groove. I did use a couple of cans of spray foam around the sill plate and weatherstripped the bulkhead door. However, this was not enough for me to be able to measure the cut in the energy bills. However since my house was an exception I will be mentioning it much more in future. See my recent blog post on the issue:
https://greenzerocarbonhome.com/wp-admin/post.php?post=1130&action=edit

You are well ahead of the pack on your thinking on swimming pool heaters. My pool heater is a standard issue AquaCal heat pump – it is very good and very economical to run. On warm days when we are heating the pool, (say a warm day in May) it exhausts cool dehumidified air into the atmosphere, truly global cooling! My pool is too far from my house to capture this and use it as AC in the house. But if ever built a house with a pool I would design it so that the heat pump for the pool would dump its cool air into the house. Free AC! I do not know of any heat pumps designed to do this but it would be fairly easy (i.e., you would need to hire an HVAC tech to do it) to run the refrigerant line from the heat pump to the head of a mini-split unit in the house. If you do this, please let me know, I would very much like to publicize stories like this. 

While I have not done this on my pool I have done something similar on my house. I do this by opening the vents (where the air filters slot in) in my air-handler units in my house in about May through September. This is when it is warm enough outdoors that I need AC indoors. Rather than turning on the AC, I open the vents on the air handlers in the basement. This draws air out of the basement and into the circulation of the house. I lean the filter pads against the open vent so that the air circulation is still filtered. The air in my basement is cool and dry. Why? My heat-pump hot-water tank cools and dehumidifies the air in the basement. This works because the ceiling of the basement is very well insulated at approx. R38 because I added 12” of fiberglass in between the floor joists. Using this source of cool, dry air allows me to avoid using the AC units for about 4 weeks in the year when previously I had to use them.  It is not a major cost saving but it is a nice one. I like anything I can get for free! If houses were properly designed, things like this and the integration of pool heating with house cooling, would be built in from the start. Sadly these people seem to not talk to each other. 

If you are seriously thinking of putting in a pool then the $15 you spend on Zero Carbon Pool could be one of the best investments you will ever make. I am saving about $3,000 a year. My pool is big, but even on a standard sized 20’x40’ pool you would save about $1,000 a year by following the pool fab four recipe. 

My next live webinar on how to get paid to cut your carbon footprint will be Thursday, July 23rd 2020 at 7pm Eastern Time. It is hosted by the Charles River Green Coalition. You must register in order to attend this event because that helps reduce the risk of Zoom bombing. You can register here: https://www.eventbrite.com/e/zero-carbon-zero-bills-tickets-111466037920

1. In what ways do you cut your non-home carbon footprint, such as that from traveling, driving, products you purchase, etc., if at all?

We minimize the carbon footprint we create before we offset the balance with audited, verified-incremental, carbon offsets that we buy from Cool Effect. I believe that you should cut where you can (e.g., with the fab four) and offset where you can’t. It is neither practical, nor financially justifiable, to cut everything to zero. So , where you can’t cut it makes sense to offset. Offsets are not that expensive. But first, cut…

We are big recyclers. We buy only organic food in the first place. We throw out almost nothing. Any edible waste goes to our chickens. The chickens fertilize our garden making our fruit and vegetable gardens very productive. And they give us eggs and meat. So we eat very well. We are not even close to being self sufficient and do not aspire to being so. But we do love the taste of asparagus in April, rhubarb in May, tomatoes and peas in June, cherries in July, peaches in August, just about everything in September, apples in October and pears even into November. Last October I succeeded in transplanting peppers and tomatoes in pots to be grown indoors (growing under LED grow lights powered by my solar panels) and we were eating them up to Christmas. Anything the chickens won’t eat (onions and citrus for instance) gets composted as does all our paper tissue products. Almost everything else gets recycled and we trash only about a single 50 liter (13 gallon kitchen waste bin’s worth) each week.

I bought a Tesla this year, which I charge from my solar panels and I drive it at 2c per mile compared to my old SUV which cost 10c per mile. The Tesla, when charged by solar panels, has a zero carbon footprint. This covers most of our travel but we still have two gasoline powered cars. When they die they will be replaced with EV’s too.

When we buy things we buy almost always local and sustainable. For examples:

• for clothing we only buy organic, mostly cotton and almost all grown and sewn in the U.S.
• for food we buy only organic and usually U.S.-grown only though we do make a few exceptions for some rather excellent Swiss cheese and Italian balsamic vinegar. I used to drink mostly French wine but now drink mostly Californian organic wines. We have visited farms that provide many of our favorite foods like tomatoes grown in Vermont, cheese made on Martha’s Vineyard and blueberries grown in New Jersey.
• construction products (wood, paints, door hardware and light fixtures) are almost all made in the U.S. including many made in New England. We buy a lot of construction products because we are renovating three properties right now. The wood that will become the flooring in the extension that we are currently building on our house will come from trees that fell down on our land. We had these sawn and they are currently drying out.
• for cars, our Tesla was made in the U.S., the first American-built car we have ever bought, before this we bought only BMW and Mercedes.
• we buy almost no gasoline or heating oil and we buy zero electricity as everything is powered by U.S. sunshine. 
• when we do travel by air (none so far this year, but not by choice) we offset the journey with carbon offsets. Any remaining purchases of gasoline, heating oil, electricity are zeroed out each year as Christmas presents from me to the other family members.

2. If you purchase carbon offsets, how do you decide where to buy the carbon offsets from? What do you look for when purchasing carbon offsets? What are your purchasing criteria?

I am quite skeptical of the claims of many types of carbon offsets especially those that depend on planting trees in the Amazon. Trees grow really well in the Amazon all on their own. Hence it is hard to say that planting trees is removing more carbon dioxide than nature would remove by herself. I buy my carbon offsets from Cool Effect precisely because they are audited to be incremental. Even then I buy only carbon offsets from a project that captures methane that would otherwise leak into the atmosphere from exposed coal seams on the Ute Indian reservation in Utah. This is genuinely incremental and it is supporting U.S. jobs and Native American tribes. 

3. If you have purchased carbon offsets, what prompted you to purchase them at the specific moments you’ve made the purchase? How did you decide how many offsets to purchase? With what frequency do you purchase offsets? 

I do it annually to offset any secondary carbon footprint we have from travel. I also offset the carbon footprint of any paperback books I sell (the vast majority are sold as e-books) and any T-shirts I sell in the Zero Carbon business. The T-shirts have the lowest carbon footprint possible because they are made from unbleached, un-dyed organic cotton grown and sewn in the USA. However, I still offset the small carbon footprint they still have.

The fab four recipe for cutting your carbon footprint will work in the southern half of the country as well as in the northern half.

From the point of view of the laws of physics a house is just a box. It has a top, a bottom and four sides. Energy comes into the box from electricity and heating fuel. Energy goes out through the walls, windows, attic and floor/basement. This is the same whether we call the box a house, an apartment block, an office or a factory.

In a cold climate you need to keep the heat in. In a hot climate you need to keep the heat out. The answer is insulation and triple-glazed low-E windows in both cases. So these parts of HITS (the I and the T) are the same in cold climate or a hot climate.

However, a heat pump (the H in HITS) in cooling mode is the same efficiency as an air-conditioner. It is only in heating mode that a heat pump has four times the efficiency of an oil-fired or natural gas-fired furnace or boiler. So the year-round gain in heating/cooling efficiency is bigger in a cold climate than a hot climate.

Solar panels (the S in HITS) work better in the southern half of the US because there is much more sun there than in the northern half. In fact, where we live in Massachusetts, we have a rather poor solar crop to harvest . The desert southwest has almost 40% more solar energy per year. This makes solar power about 40% cheaper per kilowatt hour in the southwest compared to Massachusetts. See this map from the NREL:

In addition to how much sunshine you have in your area, the price you pay for utility electricity will have a big impact on the payback period for solar panels. High electricity prices make the payback period on solar panels faster, because you are saving more money per kilowatt-hour of electricity generated by your solar panels.

Other than Hawaii, which has very high electricity prices, the highest cost for electricity in the U.S. is in New England, California and Alaska where you will pay about 20c per kilowatt-hour. In a band of states running down the center of the country from North Dakota to Louisiana, electricity is about 10c per kilowatt-hour.

So overall, with insulation and low-E triple-glazed windows cutting your carbon footprint and utility bills across the entire country and with the lower benefit of using heat pumps for heating in the southern half of the country combined with the higher solar production in the southern half of the country, HITS will benefit you no matter where you live. The recipe just needs to be fine tuned to your exact location and local financial subsidies.

Q: For new construction, would it be possible or make sense to put in loops for a ground source heat pump below the structure? 

A: I have not seen this done, but I have thought about it for new construction. Since you are excavating for the basement anyway, why not just go down a few feet more and put in ground loops? I think this would greatly reduce the cost of adding geothermal. However, I do not know if this would reduce the cost enough to compete with air-sourced heat pumps. The downside I can see is that your basement would get colder which could lead to increased condensation in summer when it is humid. 

Q: How much can a Tesla power wall store? Will it be enough for 3-5 days in case of an outage?

A: One Tesla Powerwall stores 14kWh of electricity. If you are using fossil fuels for heating then you are probably using about 20kWh a day to run all the lights and appliances in your house. If you are using heat pumps to heat or you are using AC in the summer then you are probably using about double this. Hence it is not practical to use a Powerwall (or any other type of battery) to run your entire house loads. However, this is not how most people use a Powerwall (see my blog post on uses of batteries). Most people use them as an alternative to using a diesel or propane back-up generator. So the battery or generator is powering an emergency panel which is usually the fridge, the furnace burner circuit and the circulating fans or pumps, plus some lights and a few outlets. This is typically under 1kW in total continuous load so a Powerwall can last about a day. This is usually enough to get you through a power outage. To last 3-5 days you would probably need 2 Powerwalls and to reduce the load on your batteries to just the lights, the wifi, a few outlets and the fridge.

Q: In Colorado, our grid-tied solar is restricted to 120% of historical kWh usage. Your solar panel system is massive. Is your system restricted in size OR are you actually using that much electricity? Where is most of your electrical usage in your home?

A: Net metering rules (and the subsidy rules, which are different entirely) vary a lot by state and even by town within a state and even then by utility company within a town. In MA, net metering is generous but there are many limits to net metering. Under 10kW you get 100% credit for any power you export. Above 10kW and below 25kW you get only 60% credit for the excess power not 100%. Above 10kW the utility has to approve your system and if there is, say an overloaded transformer on your street, they will not approve it. The SMART subsidy (the MA subsidy for solar power) drops to almost zero above 25kW, but then it goes up if you add a battery or install the array as a canopy over a parking lot. If you install it over a farm field and maintain the agricultural use, it goes up again. So you just have to pick through your local rules and try to optimize financially. In my experience in MA today, the financially optimal array is just under 25kW with battery back up.

My arrays generate slightly more electricity than I use throughout the year. Most of that electricity now goes on our heat pumps because we use almost no heating oil.

Solar photovoltaic panels are sometimes called solar P.V. panels to distinguish them from solar thermal panels, or solar hot-water panels, which use the heat from the sun to directly heat water. Solar thermal panels can be over 70% efficient, which sounds great compared to solar P.V. where the maximum commercially available efficiency is 22%. However, if you are using that solar electricity to power a heat pump hot water tank (please see page 66 in Chapter 2), with its 400% efficiency, you get a total heating efficiency of 84% for the solar P.V. panel that is heating your hot water with a heat pump. This is better than the efficiency of a solar thermal panel. Because of net-metering (please see page 82), solar P.V. panels can generate the electricity in the summer, and you can use it in the winter. This is not possible with solar thermal panels, which generate little hot water in winter, which is right when you need it.  Also, the solar-P.V.-plus-heat-pump-hot-water-tank option has no pipes and hence cannot leak. Better overall efficiency, energy “storage” via net-metering, and no burst pipes make solar P.V., in my opinion, a far better solution than solar thermal panels.