The Home Energy Challenge, Pt. 2

Unfortunately, my experience is that the high tech, renewable energy gadgets really do make a big difference. My electric bill went to below zero with solar PV and I’m getting about 20% reduction in my gas bill with solar hot water. In a reasonably well insulated house, the energy saving from putting in something like double pane windows is really in the noise. Of course, a more tightly sealed house could make a difference but then one could run into problems with air quality.

But you make a good point. It’s possible to take a LEED Platinum building and run it so that it doesn’t even qualify for LEED, just as it is possible to drive a Prius so it gets 36 mpg. My blog (http://netzerolife.blogspot.com) talks about my family’s efforts to achieve a carbon-free lifestyle.

OK, fair enough.  I agree that it makes sense to start with the simple things. We were able to reduce the natural gas consumption in our house by about half just by turning the thermostat to 68 degrees instead of what the previous owners kept it at. That cost exactly nothing.

I guess my problem with efficiency improvements is that the most cost effective improvements are typically for the worst cases, like houses with no insulation in their walls at all. Somehow, I’m wanting to see a kind of “Moore’s Law of Energy Efficiency”, where the technology starts getting better and cheaper exponentially just like it does for computers. Houses like mine, which were build in the 70’s when the building codes were already calling for insulation are just OK. I’d like to get them up to LEED Silver at least without laying out a couple hundred grand.

I agree with Matt - First things first and the first is reducing energy requirements as much as practical through practices (thermostat setting etc), sealing the home, adding insulation as is practical and then on to more exotic items.

Solar hot water is far easier, more efficient and more cost effective than PV power. For example I turned off the electric to my hot water tank on 1 April and it has been on 4 days since then. I expect to go another month or so before turning it on.

Lastly comes PV power or in a few locations, wind.

When one considers good policy, then you have to realize that the government paying 30% of the cost of a solar installation is part of the cost.  It must be evaluated on a level playing field.  When you look at the absolute costs of solar vs. insulation, lighting, or other basic measures, efficiency is simply cheaper. 

In this day and age, the fact that EE is mostly jobs is actually a massive positive.  Rather then have 60% of our investment going to solar panels that are almost entirely made in China, dollars invested in efficiency stay in local communities and create jobs in America.

I am actually not arguing against any single technology.  I am advocating for a performance based system of incentives that is technology neutral… meaning we reward results and those technologies that work best rise to the top.  No need for anyone to pick winners, the market will do that based on what works.  When we create an incentive that rewards one technology in particular, we stifle innovation, and make the market less efficient.

I simply am an advocate for a level playing field.

@Russ: Solar Thermal Domestic Hot Water (DHW) is not cost effective because it is unreliable.  It requires installation of two hot water systems—the expensive ST and a backup for days with insufficient sun.  From a cost perspective, ST DHW requires you to design, buy, install, maintain, control, plumb & wire for 2 DHW systems.  The ROI on that system is forever, or never. 

Efficiency of solar DHW (domestic hot water) calculated properly requires the costs of all systems, not just an observation that solar heats water efficiently.  Evidence what I say is true can be found in the results of the Solar Decathlon. You will find ALL contenders in the “hot water” and “comfort” (ability to control indoor temp) contests at the recently completed Solar Decathlon came to the same conclusion:  a heat pump for hot water and indoor heating, powered by PV.  ST was used by a few to boost heat pump performance (e.g. pre-heating a ground loop or DHW).  As a boosting system the ST system costs (size, storage, design complexity, etc) are substantially lower.  It also allows the system to be mufti tasked (pool & spa heating, winter ice melt etc).

You can find very detailed engineering and cost analysis in the manuals and drawings for each solar decathlon participant at:

http://www.solardecathlon.org/2009/team_germany.cfm

Pay particular attention to performance and systems used by the winners vs systems that utilized solar thermal as a primary system (HINT: the ST guys got POUNDED).

Hmmm. During the heating season a heat pump water heater is effectively a load on space heating eh? Why not add a glazed or transpired air collector to feed the heat pump water heater? In the cooling season you could valve out the solar collector and switch over to feeding the heat pump internally. Perhaps I’m missing something.

JoeJoe, good observation, and an interesting idea, but generally the added heating load is irrelevant and the added expense for the system you’ve suggested is unnecessary. 

In most U.S. climates, the heating season consumes less energy than the cooling season.  As you know, the DHW heat pump produces a cool air *waste* stream year round, thus it provides bonus cooling during the highest energy demand season—the summer.  In short, waste heat to boost the heat pump’s performance is cheaper to find in the winter than waste cooling in the summer. 

A properly designed structure and mechanical system easily solve your concern.  The mechanical system (including domestic hot water DHW), we use includes a solar thermal system that simply heats a large insulated tank.  This heat source is used to pre-heat DHW and (in winter) pre-heat the ground loop of a ground source heat pump.  This essentially turbo-charges mechanical systems that are already ridiculously efficient and produces waste heat that can also be used for ice melt or winter heating the DHW mechanical room…

http://www.rheem.com/Products/tank_water_heaters/hpwh/hpwhhomeowner/

hmmm… as he twiddled his imaginary chin-stache. Solarwall has installed a few systems but I haven’t found any specific cost data.

http://solarwall.com/modules/download_gallery/dlc.php?file=33
http://solarwall.com/modules/download_gallery/dlc.php?file=65

I don’t see many harvestable sources of waste heat at the residential level. Maybe the shower/sink drains and a few kitchen loads but I haven’t the slightest clue what the $/BTU harvesting costs would be. Ground source works but I’m not familiar with the $/BTU costs there either. Meh… Where’s Hal 9000 when you need him? COMPUTER… Yes Dave… What are the comparative $/BTU costs of ground source, transpired air collector, and drain heat recovery in Mumbai, Moscow, and Milan for both air and water?

I must agree about the cost effectiveness of solar hot water. I had a Schuco system installed with a Superstor Ultra stainless steel tank. My backup system was simply my already installed gas hot water heater, cost me nothing. The system ran about $14,000. I also needed to have some work done to build an insulated closet for the tank in the cold air return plenium for the former forced air heating system which we replaced with gas-fired hydronic a few years back. It was a very expensive system and probably won’t payback in my lifetime. The fundamental problem is that gas is too cheap. It’s much cheaper to heat with gas and enroll in a carbon credit program (my utility has one). Carbon credits for hot water are not more than a few cents a month. It would have been a different story if I had been heating with electricity.

I also had a lot of problems with the contractor who installed the system. He had hired a guy who didn’t know what he was doing, and the hot line coming down from the roof was leaking glycol both at the pump station union and the tank union. It took me three months to get it resolved. To his credit,  the contractor resolved the problem and acknowledged that it was the inexperience of the installation person. This points up another problem with Matt’s argument about labor intensive technologies being better: if the people who do the work don’t understand what they are doing, the results aren’t as effective as they could be and the homeowner loses. My experience is that many people in the construction industry have an aversion to learning about new technologies and doing things better. In many cases, they are in the industry because they can’t find any other kind of job (no offense to anybody on this thread who does construction and doesn’t have that attitude). Also, there is a real lack of training programs and funding to help them get trained. In contrast, PV installers tend to be well trained (working with high voltage DC is something you just have to understand how to do)  and, as was pointed out, the technology is getting much simpler to install.

The comments about alternate configurations for hot water systems are interesting. My conclusion also is that the current technology, while now much more reliable and well built than in the 70’s, is just too expensive because it requires lots of complicated plumbing which runs up the installation cost.  The cost for the equipment also tends to be too high. I looked into heat pump hot water and rejected it due to the noise. Air source heat pumps tend to be noisy. I may someday replace my gas fired hydronic system with a ground source heat pump (if I thought solar hot water was expensive…) and then the backup for my solar hot water would be heat pump. I think there are probably lots of other configurations of solar hot water heaters that could work though. I’ve been thinking of something like a sun tunnel with a concentrating collector that tracks the sun on the top. This could be installed in a fraction of the space required for a flat plate system with no plumbing. And it could be installed directly over an existing tank heater if there is a clear shot to the roof, like a sun tunnel. The concentrated light would then be directed to a heat exchanger on the tank, like the burner on a gas heater.

JoeJoe: 

1.  You need more btu storage (than your standard hot water heater tank) otherwise your system will have very little utility.  If you spend the money to capture the energy, you should design a system that can use it, otherwise your money will have been wasted.

2.  Liquid systems allow higher temp = more btu storage.  Air systems = lower temps, less btu storage.  Take home:  Use your budget to get the most btu’s for the buck (liquid system, large well insulated storage [or multiple storage tanks depending on btu needs], where stratification of water in tank can be utilized.)

IF you use solar thermal—use it properly (NOT AS PRIMARY).  Design a VERY simple loop system from solar collector to tank that starts/stops at specified temps.  Solar heated fluid is backup, NOTprimary.  Use heat exchangers in tank for:

1.  Direct DHW & preheat DHW,
2.  Direct radiant floor heating, pre-heating final leg of a ground source heat pump;
3.  Ice melt
3.  Pool spa hot water

If you cannot utilize ice melt, pool or spa heating, you will likely be better off eliminating the solar thermal system, using instead a ground source heat pump + air-air heat pump hot water heater driven by PV power.  The money you save on solar thermal goes a long way towards you PV budget given today’s PV prices.

Riddle me this… Have you modeled a solar air collector fed heat pump water heater? 

RETScreen can model solar air collectors but it doesn’t have a HPWH module (that I can find) so I’ve gone as far as I can go with free software. I’ve sent them a note expressing my displeasure. I’ve read that TRNSYS does have a HPWH module so it should be possible to compare a solar air fed HPWH against an ambient fed HPWH. Can you do that?