We took the mini plunge

I did the water heater wrap last month. I could only find the R-6.7 wrap locally when I was looking (2" vs. 3")--but now that it is complete they finally have R11 on the shelves. That's okay as the 3" was going to be a bit bulky and this installation was very clean--it's probably a better compromise. It should cut heat loss by a little less than 1 therm/month by my calcs.

I also insulated all of the hot water lines I could reach. This might be worth about 5% of our water heating load, perhaps as much as 1 therm/month although I expect less. The main factor we noticed (and expected) is that water at the taps comes to temp faster than it did before.

We haven't gone to really low flows, but we have finally got the little ones to the point that they don't try to take long showers. We averaged about 18 therms/month this summer before the water heater & pipe insulation.

Sounds like it. Before you insulate make sure that any air leakage points between the floor and crawl space are identified and sealed as best you can. If you cover them with insulation you will still have the air infiltration/exfiltration but won't be able to get at it.

We've got a walkout basement and a sub-basement arrangement and at the perimeters carpeting is providing the only real R value for the floor...which isn't much. This matters little away from the edges, since the ground below reaches an equilibrium with the house. The problem is along the walkout wall where the basement floor is above grade and is therefore conducting from the far colder ambient air. This makes an uncarpeted floor in the corner by the door really cold, as well as an uncarpeted bathroom floor along the same wall. While both need to be uncarpeted, I'm considering using an insulated backer mat and installing tile to give them the equivalent of carpeting R values. (5 mm of Easymat is R1.5.)

How many square feet?

For this year I'm trying to knock about 25% off of the previous owner's gas usage without changing any equipment and without sacrificing any comfort. (I'm not going to turn the thermostat down to the point it becomes chilly.) I've knocked down the electric by 35% already, and the water by 50%.

But this house is still nowhere near being energy efficient. Our use is about double yours.

 

Wow
New Mexico has a similar deal, but the offers cannot be stacked, so in effect it's one or the other.

While it is true that PV sizing would not be affected by switching from NG to solar heating, I try to remember that the goal is carbon reduction regardless of whether it is electricity from coal; gasoline use; or natural gas consumption. So I look for the most carbon reduction for my dollars overall. For me it looks like solar water heating and windows on the south wall.

I wholeheartedly agree with earlier posters who have ditched the clothes dryer habit.

 

One should NEVER heat water with PV unless you are off grid and you are using it as a dump load for a solar pre-heat. The reason is that converting solar insolation to heat is way, way more efficient (and ergo cheaper) than converting that insolation to electricity and then back to heat.

If your goal is either to save money, reduce fossil fuel use, or carbon footprint, direct solar hot water pays off MUCH fast in all regards. (I am not anti-PV solar,, but it only makes sense if we have done the simple, smarter things first).

A simple homemade flat plate collector can be built for ~$400. I have one on my roof near Bellingham Wa,,, not know for sun. It is a very simple loop of ~200' of 1/2" copper, sitting on a piece of scrape 3/16" steel plate, on top of 2" of thermax rigid insulation, all enclosed with 2x4 frame, covered with salvaged 28"x76" tempered patio door glass. There is a simple differential controller that turns on a 7 watt grunfos circ. pump and circulates the water into a salvaged 40 gallon hot water tank. This tank serves as a preheat tank before a gas fired demand water heater. If the tank gets to ~120f the gas doesn't fire at all.

In November, December and January, when we get little sun, I don't count on any gain, but I get about 10% most every day. If we get full sun in the winter, I get ~30%. My water comes in from the well ~54f. On a sunny day in the winter,,4 hours I get the full 40 gallons to ~75f. Starting in March we get 100% of our hot water, and come some we are over 150%.

The cost of this system was roughly, ~$150 for the pump, $10 (craigslist) for a good condition tank, ~$150 for the controller, $150 for the copper. The glass can be had for almost nothing as tempered glass panels are everywhere! I figure that the pay off is going to be about 5 years,,,depending on the price of Propane. I didn't build it for a pay off, but more just because I could.

I also have a strip of salvaged mirror on the far side of the collector, angled such that it reflects directly back into the collector. This greatly adds to the harvest in the winter,, not much in the summer. The controller that I used has a antifreeze circuit that triggers the pump to circulate the water when the temperature is near freezing so that the collector won't freeze. It kept mine from freezing at 8f with 40 mph winds. If you routinely get colder for longer periods you should consider a glycol evacuated tube system,,, comes at a much higher cost however. (When it get really cold for weeks on end like it did over Christmas I just drain it,, very simple process if you think the valving through ahead of time.

If you live in CA, AZ, NM, CO or somewhere where you have good sun and a moderate winter climate then a simple system like this is a no brainer!

Icarus

 

Spot on Icarus !
Would you mind going through your payback calculations ? My back of the envelope scribbles suggest a much earlier payback.

 

I certainly don't mind going through my payback calcs, but it is a wild nice person guess. The hardest part is the cost of Propane. We are now $1.69/gal,,, 6 months ago we were over $3. So give an average of $2 gallon.

1 gallon of Propane yields ~80k btu,, burned in a high efficiency demand water heater @85% ef. 1 but is the amount of energy required to raise 1 # of water 1f. Water weighs ~8#/gallon.

If we assume for the sake of this argument that we use 40 gallons of hot water per day for the two of us, let's also assume a temperature differential of 55f,, remember,,your mileage may vary!

So let's take our useage, 40x8x55=17,600+15% ef=20,240 btu/day

Let's call it 20k btu's day, or about (in round numbers) 1/4 gallon of propane/day, or $.50 day, or $182 per year. Now if you add in having guests, added laundry etc, lets call that $200/year.

So,, just guessing that I contribute ~75% on an annual basis, leaves me a savings of ~$150/year. Assuming my cost of $400= 2.6 years. A more realistic number might be closer to $1000 if I didn't have some of the stuff, or $1500 if I had to pay someone. or 6-10 years.

Now if Propane goes back to $3 or up to $4 or more,, of course the pay off comes sooner. Of course I haven't calculated the replacement cost of the pump or the controller in any of this,, but at least you get the idea.

Icarus

So in our case,

 

Thanks Icarus,
Even if I did have to google all your units to translate them into metric ;-)

My most wooly estimate is in estimating hot water use. How did you do it ?

 

Estimating hot water is tough. The way I estimated it was, using the 40 gallon tank, when it's temp has been raised by some degree,,, say 20f above ambient at the end of the day. I would then watch the temp of the tank, (with no solar input) and when that tank returned to ambient I assumed I had used 100% of the water, or ~40 gallons. I have also heated the tank to 120f and seen how long it takes to return to ambient, about 1 day,, assuming we are doing dishes, showering etc. Some days we use less, other days more. I think in the real world we use less, but 20 gal/day/person seems to be about right.

Icarus

 

Smart.

I have tried to estimate shower use, since that is the main culprit by far in my house. I'll not quote numbers, but suffice to say my two teenagers know it is time to leave the shower when the water turns cold.

My electricity is 8 cents/kwh, so it costs about one penny to heat 2.5 litres 40 degrees C. This is quite close to the cost of heating using propane. I'm surprised. Anyway, payback in about two years for the Diy'r, and up to 4x calling a company sounds about right to me. I'd love to roll my own, but I have a lot to learn before I can build a reliable and safe system that has to travel 25 meters from collector to tank, and survive a freezing climate.

 

Remember, you are heating water TO 40C, heating the water 40C. You are probably heating your water ~ 15-20C. From say, ~12C to 48C. Regardless, where are you located, and how severe is your freezing climate?

I have built water lines that stay free at -40C(f) in northern Canada.


Icarus

PM Me if you want to carry this on off line,

 

I think you are missing what I'm getting at. I'm not suggesting using PV to heat water, just that you can ignore the water heat load for sizing a PV system assuming that you are still grid connected. (Obviously things are different off grid, but that's a rather rate bird.) Don't size a grid connected PV system for X + water heating.

I don't doubt that the payback will be quicker for a solar water heater. Rough calcs confirm that. However, it would seem to be a mistake to rig up a solar heating system in a prime exposure, then place PV around it. PV needs the prime locations, water heat should get secondary placement since it is so much easier. If I was trying to size a system I would get my optimal PV worked out first, then figure out how to work the water heating around it.

The system you have sounds quite effective and should be space efficient when coupled with a demand water heater. That is the route I would go anyway. Freezing would be more of a concern here and I would most likely drain it for about 4 months of the year (or at least assume no net contribution for that timespan.) I would also assume that 25% of the load for the rest of the year required supplemental gas. That would put me at about 50% load replacement, roughly 110 therms/year or ~$110 with my nat. gas cost.

 

I get it now.

You are right, PV requires the prime location since PV doesn't tolerate shading at all well, while solar hot water can deal with shading way more easily.

My point is that in most instances, solar hot water should come before PV solar. Calculating simple pay back is a bit tough these days with utility rebates, federal and state tax credits shrouding the real numbers. In general, if you have the environment for PV solar, then you can do solar hot water in a snap.

As for freeze protection in cold climates,,,In addition to the kind of controller that circulates water through the collector when it is at risk of freezing, even if you use a potable water system, freeze protection is fairly easy to do, with solenoid valves and automatic drain valves. A simple temperature controller can open a drain valve, at the same time turning off the pressure to the collector, as well as opening an air vent to allow air in. The the collector can drain by gravity. When the collector temp rises enough above freezing, the valves open in reverse. I have built a similar system to draw water out of a frozen lake all winter. The pressure switch calls for water, the air vent solenoid valve closes, the pump starts. There is a high point radiator floating ball vent valve that bleeds the air out of the line so it is not introduced to the pressure tank. When the pressure switch cuts off, the pump stops, the solenoid valve opens to let air in, and the water in the line drains back into the lake through a automatic drain valve. (Or a hole in the pipe if you have a big enough pump).

In any case, if the goal is reduce energy consumption net/net, then doing hot water before PV makes sense in most cases.

Icarus

 

I highly recommend any kind of insulation.

I'm in San Diego and the first thing I did was insulate my attic. Insulating the attic and a programable thermostat significantly reduced my winter heating bill the first year I did it. Don't remember by how much, but it was way more than a few bucks.

The crawlspace under the house is next, after I run one last telephone line. I'll hire someone to insulate the crawlspace as I've had enough crawling around down there. Hence putting off the last phone line.

Then....I'll be insulating the attic again. This time the roof rather than the floor/ceiling. Now that the PV is in, nothing stopping me fom insulating the roof rafters.

Already have a fan up there to keep the heat down during the summer. But more insulation will help with that too.

 

Make sure you maintain proper vent space ABOVE the insulation to allow the attic to vent moisture out. Attics should have intake and exhaust vents,,, intakes over the walls, exhaust at the ridge or gable ends.

Icarus

 

A smaller package makes the size of many of the projects smaller/cheaper/more manageable. I was in 1400 sq. ft. homes for most of the past 17-18 years, including the one before this with a few years in between at ~1800 and 2000.

With the kids getting bigger it was well past time for us to take a step up in size. We are at ~2800 sq. ft. including the finished basement & sub (makes me feel a little bit better about my nat. gas usage...but only a little.) 1994 vintage, super tall ceilings in the entrance/living/dining so the total volume and surface area is even greater than it should be. (It's not what I would have built, but that's what seemed to predominate in the market, and it looks great.)

The 30 feet from top ceiling to bottom sub-basement floor is being done with a single zone HVAC system, not a smart/efficient/comfortable design decision...so stratification of the air is my nemesis with regards to comfort/efficiency. Basically if it just moved hot air (summer or winter) from the top to the bottom I think I could cream my energy usage, but it's not configured to do that. I've had some success in balancing the system and hopefully correcting the worst bypass and infiltration problems. I've had to do a more vigorous CFL upgrade (requiring many new fixtures) than in other homes and from what I can see my annual electric use will be a little less than any of the other homes I've lived in despite the increased house size and the increased demands of growing kids. I didn't have many of my changes in place during the summer, so I'm looking forward to finding out if all the sealing work will knock AC use down a few notches this next go round.

It's a concern for me as well since I would need to run about 30 feet vertical with the piping and have to do a clean enough install that the homeowners association wouldn't object. The bigger issue is that for tidiness I would also need to buy the demand water heater and convert the existing water heater into the storage tank. (I have loads of space, but I don't want to create a two tank clutter.)

 

Godiva,

Adding to the above, I'm pretty sure that the recommendation is not to insulate the rafters unless you are converting the attic into a conditioned space. I was considering doing the same thing as you in one area until I studied it a bit more.

The insulation/seal envelope is around the heated and cooled spaces. The attic should be at ambient outside temp. Since you will have lots of air movement (by design) in the attic space to prevent condensation, the insulation might not do anything useful in the presently open rafters.

If I understand correctly, cathedral ceilings are different in that they are enclosed and include a vent space against the roof sheathing. The insulation fills the rest of the rafter space. I have a mix in my home.

Maybe I have it wrong, but I encourage you to study/research this carefully before you do it. My instincts about it seem to have been incorrect so I cancelled my original plans to insulate some rafters and knee walls on the exterior side of a storage area for the same reason. (I instead created a better seal on three access panels along the interior wall, and foamboarded the back of each and that really helped the adjoining room--easily cutting the losses there in half.)

There might be some advantage though in using some sort of radiant (purely reflective?) barrier on the rafters for summer. The radiant heat load then is considerable and the heating of the air is part of what the ventilation is there to handle. It might even have some sort of application on clear nights in winter as the roof will be radiating to the sky, subcooling the attic space below (the differences of absolute temps each raised to the 4th power is a heckuva driver even for a tiny radiant factor since outer space is at a very low temp.--you should see my telescope optics dew up as a result.) But this is just speculation on my part, I've not researched this with respect to attics. If it makes any sense, someone will have a guide online as to how to do it without screwing something else up.

 

Assuming you have a flat ceiling and a pitched roof with attic space: Insulate on the floor of the attic to the maximum amount you can afford, depending on climate, above ~R-40 begins to be diminishing return. Pay particular attention to the area over the exterior wall. Maintain at least a 1" airspace above the insulation and under the roof deck to allow free air circulation. Insulation baffles are important where the insulation could plug the vent space. Vent at a minimum of 1/150 with 1/2 low and 1/2 high. Ideal vents are continuos soffit intake vents and continuos ridge vents. Make sure of an adequate vapor barrier on the conditioned side of the area. Additionally, if you live in a climae where summer heat gain is an issue, you could install a radiant barrier on the bottom of the rafters to reduce heat build up in the attic. In this case soffit vents and ridge vents are a must to allow the built up eat to escape.

If you have a vaulted ceiling, insulate to the maximum volume, keeping at least 1' of air space above the insulation batt. Low soffit vents, and ridge vents are a must.

Insulating crawl spaces under houses: Depending on climate insulate between the floor joists to a minimum of R-19. Venting is an interesting issue depending on climate, but the UBC requires a 1/150 ratio with foundation vents around the perimeter of the foundation. A 6 mil plastic vapor barrier should be placed over the soil.

The problem with venting is in summers in cold climates when there is summer humidity (IE The NE US, and I suspect the American south). The warm moist air, drawn under the house comes in contact with the cooler earth under the house, causing the humidity to condense. There is considerable argument as to what the correct strategy is. My personal theory is to provide lots of vent area for a free exchange of air such that the water can't condense.

Icarus

 

Way to go! After skimming the threads, I didn't notice if anyone asked the following: Did you check to see if your power co gives rebates for your old one?
Both of our fridg's are now less then 3yrs old, but we traded out the prior ones in our home by putting them in our rentals, when the (even) older rental fridg's were having probs. Yes, it really made a big difference, too.