Thriving On Low Carbon

A Proposal for Amending the Passivehouse Standard for New England

With the help of a number of colleagues involved in Passivehouse I've been working on how this standard could be amended for use in New England and similar climates in a way that would remedy the most significant deficiencies, which I see as:

- the PH std has the same annual heating and cooling demand (AHD, ACD) limits anywhere, which leads to extreme solutions in severe climates.

- the resultant focus on meeting the AHD limit in the more severe climates diverts focus from the overall primary energy consumption of the building and its occupants.

- the PH std limits are set per unit of usable floor area (TFA), which creates the perverse incentive that larger houses meet the std more easily. Perhaps more fundamentally, the PH std, as most if not all other standards, sidesteps the core issue of resource use equity.

- the PH std counts solar input from direct gain solar heating and solar thermal hot water but does not count solar electricity to be used in meeting the std.

- the PH std does not require performance reporting beyond the 0.6 ACH50 blower door test.

After some drafts, I'm ready finally to publish this proposed amendment and see where it goes. Other countries and regions of countries have modified the Passivehouse standard to suit their goals. This proposal aspires to change how people (especially New Englanders) think about minimizing the environmental impact of houses and people. Minimizing primary energy consumption and basing the standard on occupancy rather than on area will evolve an already robust standard to a more effective and more ethical level.

It is not expected that the organizations maintaining the existing standard will welcome or adopt the key aspects of this standard. If Passive House New England, which is not aligned with either PHI or PHIUS, sees value in this proposal, it may begin to develop its own certification process. At the least, the aspiration is that this proposal may guide a well-focused and thoughtful exploration of how to live ethically and effectively on this planet for practitioners and clients, rather than aiming blindly at what are ultimately arbitrary numbers despite our best intentions.

I'm interested to hear what people think! See the attached PDF for the proposal. Download PH NE amendment V3

5,000 kWh

Yesterday the solar electric system passed the 5,000 kWh milestone since we first came on line. This is about 9-1/2 months of production. I'm now guessing we may be headed to a first year production of 6,500 kWh! Another guess is that we'll end up with a usage of about 4,000 kWh, so a net export of 2,500 kWh (currently close to 1,800 kWh, dating from the meter switch on 5/25/11, a couple of weeks before the PV system came on-line).

It becomes an interesting question - what to do with the surplus? And what to do if we follow through with our original intention to install a wood stove (which still is a good idea, since it provides heat in a power outage) and build up even a larger credit? The credit can be allocated to another meter, of course. Perhaps I should encourage Jill to take up arc welding....

PVs and credits and bills (Oh my!)

This morning we reached a new high for the credit we've built up in terms of net exported energy - 1,753 kWh. The previous high was 1,738 on December 3rd, then it dropped to a low of 1,477 on January 28th. This winter we were net importers in December and January, and I discovered to my dismay that even though I'd built up a credit of over $300 with Nstar, I was getting billed for the energy we imported. Looking closely, I learned that I had Nstar as my energy delivery company, and Coned Solutions, via Cape Light Compact, our municipal aggregator and default supplier, as my energy supply company. Having two separate companies is part of the deregulation process - you get a choice of who supplies the energy, but not who delivers it (owns the wires). It turns out that Nstar credit doesn't offset Coned supply charges. The simple solution, that doesn't make Cape Light Compact happy, is to switch to Nstar as the energy supply company. The rates are within hundredths of a cent per kWh, but that actually doesn't matter if we are net exporters - in fact, a higher rate allows us to build up a larger credit, which we could allocate to another meter.

Winter temperature data

We've been heating for the past year plus with a point source of heat - the Fujitsu minisplit heat pump in the living room. I've been logging temperature in the main space, in our second floor bedroom, the basement, and outdoors. You can see that the upper level varies more - it drops more at night, as it is heated by natural convection from the first floor, and it rises above the main level on sunny days, as it has proportionally more south glass and less shading. The basement drops through the winter as the ground cools (and the heat pump water heater removes some heat, while the freezer and PV inverter put some heat back in).

Average upper floor temperature was 68.1F, main level 69F, basement 52.6F, and outdoors 37.8F.

Professional Leadership Award

I had the tremendous honor to be given the Professional Leadership Award by the Northeast Sustainable Energy Association at the recent Building Energy conference. The award recognizes work of exceptional quality, integrity, and generosity in sharing knowledge. It's wonderful to be acknowledged by one's tribe...

Getting into hot water, Part 3

When the oil boiler went away the hot water tank did also, and this gave me an opportunity to re-locate the new water heater directly below the two bathrooms. This reduces the wait time to get hot water to the tap substantially, and the tank is now only half the distance from the kitchen as well.

When hot water leaves the tank it goes through a Caleffi thermostatic mixing valve (TMV). I installed this in case I decide to install solar DHW, because solar can make very hot water that carries a scalding risk. A TMV is set to a maximum discharge temperature, which it holds regardless of the inlet temperature. The TMV creates this mixed temperature by mixing hot water from the tank with cold water. Colleagues of mine have found that some TMVs, even when set at maximum temperature, still mix in some cold water. I tested the Caleffi and it doesn't do this, which is a nice feature in a solar DHW system - when the water temperature gets right down to the minimum usable temperature you don't want cold water mixed in, because that will cause the back-up heat to come on.

Once the mixed water leaves the TMV is goes to the distribution system. The DHW distribution system in House 5 is a home run system. There is a manifold for the hot water (and one for the cold water) that has a series of connections with shut-off valves, and each connection has a cross-linked polyethylene (PEX) tubing run that goes to an individual fixture. In my house, these are 1/2 inch, but if I were to do this myself from scratch they would be 3/8 inch for most fixtures. One of the advantages of a homerun system is usually shorter wait times for hot water than occurs with a traditional trunk and branch system. The smaller the tubing, the faster hot water gets to your tap. Having a shut-off valve for each fixture allows an individual fixture to be repaired or replaced without having to lose the function of any other fixture.

Here's the manifolds above the DHW tank, the cold manifold is behind the hot one:

Another efficient approach to getting hot water quickly to each fixture while wasting minimal water is to use an intermittently operating recirculation pump (Taco D'Mand). My very smart colleague Gary Klein has written extensively about the benefits of one of these systems (Gary Klein powerpoint) and here's a simple schematic he drew of one:

Notice that the hot water line continues back to the DHW tank after the last fixture branch. When you are in the bathroom, you push a button (it can also be set up with a motion detector, to work automatically) and the pump turns on, sending hot water to you at several gallons per minute. When it reaches the pump, the pump turns off, and you have hot water in a very short time, and almost no water went down the drain while you waited. If the water in the line is already hot from a recent draw, the pump doesn't come on. This clever system is a variation on the old continuous recirculation systems that waste both thermal energy (because the recirc loop is always hot) and electricity (because the pump runs all the time.)

The larger and more spread out a house is, the more benefit from this type of system. It really makes sense to look at each house and evaluate the best approach. My colleague Michael Chandler suggests that a modified home run system, where a single 1/2 inch line runs to a bathroom, and each fixture uses a 3/8 inch branch off of that, is the best, at least for a modest sized home. That approach means that once someone used hot water in the sink, for example, there is hot water available for the shower or second sink with no waiting.

Eight months of data - On the way to net zero

I've been traveling a lot for the past several weeks - teaching three days in the Passive House Consultant training, and about Deep Energy Retrofits and Zero Energy Houses in VT, IL, and WI. Next week is Building Energy 2012 in Boston (you ARE attending, right?) then I get to stay home for a while!

We now have eight full months of measured data, beginning in July 2011. The solar electric system came on line the afternoon of June 9th, and the commercial meter from NSTAR was installed May 25th, so I have our net energy usage from May 25th (we've exported a net of 1,590 kWh since then - I estimate we had 137 kWh on the meter when the PVs came on line) but I don't have sub-metered usage until some time in June,

It's been an astonishingly warm winter so far. We've had 73% of typical heating degree days. It has been slightly sunnier than last year (using PV production at the Eliakim houses as a surrogate). So this first year is unlikely to be typical in the long run (although I could get used to it!) As an example, in January last year we used 418 kWh in the heat pump, and this year it was 277 kWh. From July 1st to March 1st, we've used 2,639 kWh. the PVs have made 4,107 kWh, and the net exported is 1,468 kWh. I think we'll use less than 4,000 kWh this first 12 months, and I'm guessing the PV system will make at least 6,000 kWh. The surplus would power an electric car for 6,000 miles, which is more than our on-Island miles (Jill is driving 3-4,000 miles annually - her car stays here - and I'm in the 8-9,000 miles/year range, but almost all is off-Island).

Here's the Used/Produced/Net data by month:



It's clear that shading from trees hasn't affected us as much as I expected. It's most evident in December, as expected. Some people say that the PVWatts software we use to project production is quite conservative. Sunpower, the manufacturer of the PV panels South Mountain Company installs, says that there are important aspects of their panel technology that lead to higher production per watt than other products, and this may be part of what we're seeing. In the chart below, the predicted production is before any shading. Even with modest shading (one large tree to the south) the system has produced 13% more so far than the predicted unshaded output. Woohoo!

And here is the energy usage by end use (R/F is the refrigerator and the 15 ft3 chest freezer in the basement):

The heat pump is the most varying end use, peaking in January, the coldest month. There are other interesting trends. The energy used by the refrigerator and freezer drops from the summer to the winter, as the spaces they are located in get cooler. This both increases heat gain through the cabinet and also makes the compressor work harder. Conversely, the energy going into heating DHW increases, as the losses from the tank increase as the basement cools off, and the incoming water temperature drops. Cooking energy peaks in the holiday season - much more baking - and drops the last two months, partially due to all my traveling. Jill doesn't cook when I'm gone.

Here's a closer look at DHW usage and energy:

Again, usage dropped off when I was traveling, and energy in per gallon increases from the summer.