Image Credit: Chris Stratton and Wen Lee
Image Credit: Chris Stratton and Wen Lee An axonometric view of the house and garage. The water heater is a long way from the point of use in the two bathrooms — a waste of energy and water. A hot water circulation pump fixed that, but a new water heater is still down the road.
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Editor’s Note: This post is the first in a series by Chris Stratton and Wen Lee, a husband-and-wife team living in the Los Angeles area who are turning their suburban house into an all-electric, zero-net energy home. They chronicle their attempts at a low-carbon, low-cost, and joyful lifestyle on their blog Frugal Happy. This post was written by Chris.
We just moved into a new place.
We are in the process of learning how to live in a new home, a new city. My wife wanted to move back to her hometown in Southern California to live near her family. She proposed that we leave the Bay Area for a year or so and live in the house she grew up in. I would finally have a house to fix up, something I’ve wanted for a while. So I agreed and now, about a year after making that agreement, here we are.
We knew from the outset that moving to the LA area would be challenging. We are both passionate about environmental issues, particularly climate change. A lot of the challenges that we’ve encountered are related to our environmental values.
House basics
The house is a three-bedroom, two-bath 1,400-square-foot ranch with an attached, slab-on-grade garage (see image #2 below). The house was built in 1963 and sits on a 5,200-square-foot lot in a small city east of Pasadena. We would like to fix up the house to make it more comfortable, efficient, and pleasant. These upgrades would be not just for us, but also for the family that moves into the house after us. There has been deferred maintenance on a lot of the systems of the house, so it’s a good time to do some major upgrades since the equipment is due for replacement anyway.
Both to keep costs low and to seize a huge learning opportunity, I intend to in-source as much of work as possible (that is, do it myself or along with some help), all while not sacrificing quality or safety. Inevitably, some things will need to be sacrificed: likely money and (especially) time.
I’m trained as an architect and have been working as a building science researcher for the last five years, so I do have a fair amount of technical knowledge and skills. But even so, this project is by far the largest and most extensive one I’ve undertaken. It’s intimidating and, frankly, scary. But that’s how we learn and grow, I guess, by undertaking ambitious projects that make us uncomfortable… right?
After thinking through the priorities for the home renovation project, it came time to begin getting more specific on what we want to do to the house. To make the project feel more manageable, I tried thinking about the different systems of the house separately. I’m all too aware that each system affects the others, but it’s just too much to attempt to think about the entire house all at once, at least at the outset. So instead I would begin addressing each system and then later attempt to put them together and reconcile/optimize inter-relationships.
Building envelope
The “building envelope” is the technical term for the boundary that separates the inside of the house from the outside. Ideally it’s continuous and robust, but usually… it’s not. The building envelope does two main things: 1) it forms an air barrier to keep the inside air in and the outside air out and 2) it insulates the inside from the outside to keep the house warm in the winter and cool in the summer. There’s lots more to say about the building envelope, but this is not the place.
As for our house, currently only the ceiling is insulated; the walls and subfloor are not. None of the house has been air sealed, particularly. It’s pretty drafty. There’s a test to measure just how drafty it is, and after you have that number you can use it both to measure your progress in air-sealing the house and to compare it to other houses. We’ll talk more about this test later.
I’d like to get the ceiling and walls insulated to levels similar to those required in new California homes. I’m ambivalent about insulating the subfloor in this climate. The crawl space provides free cooling in the summer and isn’t much of a liability in winter. Also in LA, we don’t really have winter, we have “winter.” So right now I’m leaning towards not insulating the subfloor, but my position may evolve (as the politicians say). I’d like to get the house’s air leakage rate down to around the upper limit allowed in new California homes. What that number is and how to go about achieving it may be a subject for a later post.
Ventilation and indoor air quality
Quick primer: There are two main types of ventilation in residential buildings: local exhaust ventilation and general (a.k.a. “whole-home”) ventilation. Local exhaust ventilation removes pollutants being generated from specific sources in the house. Rooms in the house that commonly need local exhaust are bathrooms, the laundry room, and the kitchen.
Also, the whole home needs to get adequate fresh air. If the building envelope is tight, there’s not much (presumably fresh) outdoor air getting in, so there should be some kind of whole-home mechanical ventilation system. In addition to ventilation, any combustion appliances in the home (gas furnace, gas water heater, gas…anything, fireplaces, etc.) also need their own dedicated means of getting combustion air into and combustion pollutants out of the house.
Our house needs local exhaust ventilation in each of the two bathrooms and in the kitchen. It may or may not need whole-home ventilation, depending on how tight I can (or choose to) make the building envelope. As for combustion appliances, our plan is to eliminate them entirely.
Until 2014, the bathrooms in this house had no exhaust fans at all. There aren’t too many U.S. climates where you can get away with that, but Southern California is one of them. A couple years ago bath fans were added, but they were installed to exhaust into the attic, albeit with the ducting pointed in the general direction of a gable vent and a rafter bay vent, respectively (see image at left).
Venting bathroom fans into the attic instead of to outside is a bad idea. (The building code agrees.) You’re spitting warm, moist air into a semi-enclosed area. If it’s the winter the moist air will cool down enough that the water vapor becomes liquid water, and that liquid water will condense on whatever surfaces you’ve got up there. Insulation, wood, whatever.
And organic matter plus moisture equals mold and rot. Think mold spores in your attic getting into your HVAC system and getting distributed throughout the house. Think rafters and ceiling joists quietly rotting away, jeopardizing the structural integrity of the house. It’s bad news. Again, because of our warm, dry climate, we get a bit of a free pass. But still.
These bath fans need to be vented directly to outside. I’ll probably do that using wall caps on the gable wall. In the kitchen, there’s a range hood that’s ducted out through the roof. It seems to work well enough, but could be a little more quiet.
This is by no means a complete list of the ventilation and IAQ concerns and measures associated with our house, but it’s a decent start and will do for now.
Domestic hot water
Currently there’s a 40-gallon, 60% efficient natural gas water heater in the garage at one end of the house, and both bathrooms at the other. To get hot water in the bathrooms requires flushing out all the cold water sitting in the hot water line. This is roughly 3 gallons of water! In the desert! During a drought! There’s a lot of room for improvement. (See Image #3 below.)
Eventually we want to change the system itself to be more efficient, but in the meantime we resorted to some behavioral stopgap measures to at least reduce the wasted water somewhat. We began not using hot water in the bathrooms except for showers. And for showers we put a 5-gallon bucket under the faucet to collect the cold-water-in-the-hot-water-line and use it to water plants.
The plan is to switch out the natural gas water heater with an electric heat-pump water heater and to put an on-demand recirculating pump in the farthestmost bathroom. Heat pump water heaters can be 300% (!) efficient and the “recirc” pump will eliminate water wasted while waiting for hot water. These will both run off of electricity generated by solar electric (photovoltaic) panels installed on our roof. We actually already got the solar panels installed and I installed the recirc pump about a month ago. They both work great! These were two relatively straightforward projects that 1) could have an immediate impact, 2) don’t impede other projects and 3) can be done relatively quickly. So, we just went ahead and did them “out of order.”
Space conditioning
The house currently has a central forced-air heating and cooling system. There’s a 3.5-ton air conditioner and a 75,000 Btu/hour natural gas furnace, both installed in the mid-1990s and controlled by a non-programmable thermostat. We haven’t used either system since moving in.
The plan is to remove both systems and all the ducting and install a two-zone minisplit heat pump. There might need to be a short run of ducting for the head unit on the south end of the house to condition the three bedrooms. But if there is any ducting, it will be low pressure loss and located inside the building envelope.
Electrical
Currently the electrical system is slightly undersized and outdated from a safety standpoint. The 100-amp service panel is original (i.e., 50+ years old) and is made by a company called Zinsco. Some Zinsco electrical service panels are known to have serious and dangerous design flaws that can prevent the system from automatically shutting off when too much power is being drawn. The company went out of business a few decades back. I don’t know if our panel is one of the flawed ones, but I don’t want to take any chances. Also, none of our electrical outlets are grounded.
Our plan was to replace the service panel with a 200-amp one when the solar panels are installed and then to rewire the house with grounded 3-wire cable. We’ll also need to install dedicated 240-volt circuits for the induction range in the kitchen and the heat-pump water heater in the garage. We want to eliminate natural gas appliances from the house and run everything off of the electricity generated by the solar panels. When the solar panels were installed, the contractors also installed a new 200-amp service panel. So that part’s done.
Up next
So that’s an overview of the systems we plan do work on. It feels like kind of a lot. But I think (hope) I’m up for it. Other topics to be considered are budgeting and sequencing the project, permitting, what we might do ourselves and what we will contract out. And how long all this stuff might actually take to get done. Also down the road it might be worth discussing each of these systems for fellow building science energy nerds who are keen on the technical stuff, as well as something about how all these bits work together as a system. Or at least how I hope they’ll work.
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19 Comments
"(resisting the urge to make
"(resisting the urge to make a joke here)"
Not sure what this means
Ugh
You're both right. Ill advised. My apologies. Retraction requested. And I thought I was going to get dinged on the technical stuff...
Reference removed
The post has been updated, and the comment removed.
Uxorial figure here
Hi hi -- wifey here. Just confirming that this line was more an inside joke that's funny between the two of us in the house, but out of context it's kind of awkward/inappropriate/weird. Soooo probably best to remove (thanks Scott). It's not the point of the article anyway. Let's talk about something else! Thanks all for reading and Chris and I are excited to share more about our house project as this blog series continues. :) -Wen
I'm looking forward to more! @Chris Stratton & Wen Lee
I really enjoyed the "...Giant Foam Box Part I..." pictures & writeup!
Can Chris really levitate like that? :-)
https://static1.squarespace.com/static/5565e96ee4b032025ebab985/t/5a613db153450ab0051a6bec/1516322228193/insulation+jump.jpg?format=500w
The pre-existing AC and furnace seem grotesquely oversized for even the "before upgrades" cooling & heating loads. But won't a 2- zone mini-split also be a bit oversized for the "after" picture? Finding one that has a minimum-modulated output that's less than your average load (per zone) could be difficult (or maybe that water has already passed under the bridge?)
With an available crawlspace to work with maybe a 3/4 ton or 1-ton mini-duct cassette type mounted in the crawlspace might be a better fit to the loads, with higher comfort, higher as-used efficiency. Most 2-zone compressors can't throttle back to less than 6000 BTU/hr or so, many are even higher. A 3/4 ton Fujitsu 9RLFCD cassette can modulate down to 3100 BTU/hr at HSPF/SEER test conditions, and could probably cover the loads pf this way-better-than code house at Temple City's 37F & 93F 99% & 1% outside design temperatures. If not, the 9RLFCD, the 12RLFCD ( 3,100 - 13,600 Btu/hr cooling, 3,100 - 19,400 Btu/hr heating ).
Oblique reference to uxorial figure & ethnicity, mayhaps? @ #1
[previously quoted material deleted]
About that technical stuff... @ Chris
"And I thought I was going to get dinged on the technical stuff..."
The polyiso/fiberglass/polyiso sandwich in the roof insulation is a bit of a moisture trap. The path to drying for any moisture that finds it's way into the fiberglass layer is through 3" of rafter ( probably ~0.2-0.3 perms?) into the vent channel and (maybe 0.3 perms ?) through the fiber-faced 1" polyiso.
In dry temperate Temple City it's should be OK, but doing that in a wetter, or heavily heating dominated climate is potentially problematic (even if the exterior polyiso-R is sufficient for wintertime dew point control.) Was the stackup sanity checked with WUFI drying simulation?
http://www.frugalhappy.org/blog/2018/3/11/insulation-ceiling
https://static1.squarespace.com/static/5565e96ee4b032025ebab985/t/5a5edb5ce4966b3c3bd71d17/1516165991687/IMG_5456.JPG?format=750w
Hash tags
I don't want to further derail what looks to be an interesting blog, but can someone explain to me why an explanation about roof venting is followed by "#science"? It isn't a link, what is the purpose?
And while you guys are at it, can you also explain why I sometimes get referred to as "@malcolm"? Bear in mind I'm well over fifty. This stuff is new to me.
Dana, you're reading ahead. :)
Yes, I'm afraid that ship has sailed/water has passed under the bridge/(insert other favorite water-flow-as-time-passing idiom here). You're right that we're still oversized. I should have subjected my thinking to GBA scrutiny beforehand, but alas. Went with
Condenser: MXZ-2C20NAHZ2-U1 (22kBtu/hr 2-zone)
Wall unit for common area: MSZ-FH12NA (12 kBtu/hr)
Ducted unit for bedrooms: PEAD-A12AA7 (12 kBtu/hr)
My load calc consultant came up with recommendations of ~12 kBtu/hr cooling and ~10 kBtu/hr heating. I realize the system I installed is way above those numbers, but I was under the impression that a DC variable speed compressor can still operate efficiently even well below its rated output?
Currently, we're still half a house short of a thermal envelope so I don't know how oversized it is and just how much short cycling we're going to have. But even now it doesn't run much... The summer will be more of a test. But we should save this discussion until I actually write about the DIY minisplit installation! :)
Malcolm
I'm not sure what the etymology is, if it originates from phpbb (an online forum) coding where you cant type @username and the person who has that username will get a notification that someone has mentioned them in a conversation, or if it just comes from @ meaning at. But either way, when someone types @malcolm they're just saying that the following comment is directed at you.
#sciences come from the using the pound symbol as a "hashtag" followed by a word or very short phrase to show what topic was being discussed. It's similar to a title but often comes after. I'll be honest, I don't really get this one either. But at 38 I'm still young enough that I've been exposed to it often enough to get used to it.
The limits of modulation @ Chris Stratton
Yes, the ECM motors driving the blowers & compressors run very efficiently well below it's rated output (usually more efficiently than at the modulation levels chosen for rating). But they aren't infinitely variable. The 2C20NAH compressor can only dial back to 6000 BTU/hr total in cooling mode, half the recommended 12K (which probably had at least some oversize factor), and only 7400 BTU/hr @ +47F in heating mode, which is 3/4 of the recommended 10K.
That means the compressor will be cycling on off a LOT more than modulating, and there's an energy penalty with every spin-up.
The PEAD A12's minimum cooling output is 5000 BTU/hr, 5800 BTU/hr @ +47F heating which has to be WAY over half your cooling & heating loads, That's going to have spin-up losses too.
The FH12 can at least dial back to 2500 BTU/hr cooling 3700 BTU/hr heating, so it at least has the capability of modulating some, were it not for the modulation limitations of the 2C20 compressor. It'll only be able modulate down to run at it's minimum speed when the other zone is also calling for heat/cool. The combined cooling minimum of the two of (5K +2.5K=) 7500 is still over half the 1% cooling load, and the combined minimum (5,8K + 3.7K=) 9500 BTU/hr, 95% of the recommended 10K at it's MINIMUM modulated output.
With the equipment you have it'll probably be more efficient to turn the PEAD A12 off until it's really needed, and rely mostly on the FH12, to get at least SOME modulation out of the system, with fewer spin-up cycles on the compressor.
Not having enough load to modulate and run really efficiently is a common issue in high efficiency houses. But the good news is that since the load is so low the hit in efficiency doesn't add up to a whole lot of additional annual kwh.
Back to construction
Lucky you! Looks like the rafters are sitting flush on the top plate. Rafters here in the Midwest are birdcut so we lose 1/3 of the height between sheathing and top wall plate. So you can insulate better above the wall w/o raising the roof. Although it would still have to be with nasty closed cell foam to get near code. At least that would close up wiring holes around the perimeter. Only need to foam inboard to where standard insulation can be deep enough.
You're in CA with all that sun, I'd go with solar water heating. You can pick up 2-3 panels for less than $400 used on Craig's list. If not, I can find them here and drive them out for a vacation. They usually are $3000 per (that's why they say DHW solar is dead but far from it at used prices). Today there's one complete set up (vacuum tubes) for $1200 all inclusive (tubes x 30, pump, controls and 80 gal. water tank w coil).
Cheers, PK
@Calum
Thanks for that! # explanation.
@ Dana re: roof assembly
Yeah I recognized the fiberglass layer was a potential moisture issue, but like you said, we're in a hot dry climate. I think we'll be okay, but it's not ideal. I wasn't sure what other insulation to put in that layer -- foam's expensive and we don't need an R70 ceiling. I looked into WUFI hygrothermal (?) analysis, but the only software I could find was $850. Is there a free (or at least cheaper) version? I don't have a WUFI software budget; I'm just some guy, y'know? :) I would definitely take greater pains in a less forgiving climate.
There are freeware versions available @ Chris Stratton
The WUFI Light freeware (license only good for 4-weeks at a time) can analyze 1-D hygrothermal stackups. It'll tell you how much moisture can move through the fiber faced polyiso over time, but won't tell you how much additional moisture would be moving through the rafters, etc.
https://wufi.de/en/service/free-wufi-versions/
@ Dana re: HVAC sizing
Hmm, yes sounds like I should have done more due diligence on the minisplit sizing. Thanks so much for the evaluation. Turning off PEAD A12 until the wall unit can't keep up sounds like a good idea. And regarding the efficiency losses being a percentage of an already small number: over the last 12 months we've generated on-site (4kW PV array) about three times as much energy (gas + electricity) as we've consumed. We'll see if that trend continues now that we actually have a space conditioning system. But for what it's worth, the efficiency losses of an oversized system may be somewhat moot?
@ Paul re: eave insulation, solar thermal
You're right, Paul -- I've got the full height of the 6" rafters to work with at the eaves. Not quite as good as a raised heel truss, but I'll take it. Haven't decided insulation/vent strategy yet for the attic area yet -- open to suggestions. Leaning toward rigid foam at the eaves, both to facilitate venting and to maximize insulation in the small space above the top plate. Sorry if any of the terminology I'm using isn't right, hopefully clear enough what I'm trying to say. Plan to bury the rest of the attic in loose fill cellulose, after air sealing attic floor and perimeter? Any notoriously leaky areas to look for?
As for solar thermal, I went back and forth on this for a while. In the end I went with PV and a heat pump water heater (yet to be installed). If I ever do another house, I'll consider solar thermal because the physics make so much sense. But for this house, I've decided that the added complexity just wasn't worth it. Not sure if this was the "right" decision, but I'm at peace with it.
Efficiency loss somewhat moot, but not entirely @ Chris Stratton
From an energy use point of view it doesn't much matter, but from a creature comfort point of view it does, even more so in areas with higher latent cooling loads than yours. In your climate the latent cooling loads are low, but not negative. (In coastal northern CA they're mostly negative).
At low sensible loads with a very low duty cycle on the cooling you may not always achieve adequate latent cooling. Running them in "DRY" mode would take care of it on most days if it's getting sticky inside, but even then the low duty cycle might interfere with latent cooling performance.
Since the minimum output of the compressor is higher than the minimum output of either the PEAD or the FH12, it doesn't matter a whole lot which one you turn off. The FH12 is inherently more efficient than the PEAD. But the key factor is that in cycling mode it's more efficient to have just one zone cycling on/off than two. The additional load the FH12takes on by having to support some of the adjacent zone's load will also improve the duty cycle, improving it's latent cooling a bit.
The GOOD thing in your case is that a heat pump water heater provides a substantial amount of latent cooling, and it will be reducing both the sensible & latent cooling that has to be handled by the Mitsubishi.
cooling should be easy
I have a 1950s retrofit in the midwest, hot humid summers. I cool it with a $50 used window air conditioner, turn it on in July and turn it off in September. Around 500 kwh, or $50 per year in cooling costs.
I can't comprehend how homes in mild climates manage to have complicated air conditioning problems or high costs.
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