Saturday, April 24, 2010

On Again

Forrest arranged for us to visit a house he is working on with a heat recovery ventilation (HRV) system, so that we could get an idea how noisy HRV is. On Friday, we drove up to the place. The house is a job that Forrest has almost completed. There are still a few items yet left to finish, and the owners had graciously consented to let us check the HRV out since they are away.

Surprisingly, the HRV system is almost silent, even on the highest setting. The only time I could hear anything from it was when I was standing directly under the vent in the bathroom, and that was just the sound of the air coming out of the duct. Forrest also turned on the forced air furnace, and that was much noisier, I guess because the amount of air being pushed through the ducts is larger.  Paul, Forrest's partner, opened the attic and let us take a look at the HRV in operation. With the attic door open, you could hear a distinctive hum, but the vibration was not transferred to the structure of the house, unlike a forced air furnace, because the HRV is mounted from chains connected to the frame of the house with springs. This acted as a sound damper, removing any vibration. Sound propagation through the HRV ducts is also limited by putting in lots of right angle turns. These break off the paths through which sound waves can easily propagate.

We still have some concern about the geothermal heat pump. The big pump that sends the heat exchanger fluid into the ground and the compressor that either extracts the heat from the fluid or puts it in are both likely to generate vibrations. Just like a forced air furnace, they can't be hung from the frame of the house because they are too heavy, though there are some measures that can be taken to isolate the heat pump from the frame of the house. We discussed putting the heat pump in the garage and running an insulated line to the heat exchanger in the mechanical closet instead of mounting the heat pump in the mechanical closet. We need to have the heat exchanger in the mechanical closet because that is where the manifold is for the radiant heat system. Of course, we would also need to figure out how to engineer the air conditioning. The air conditioning is never likely to be quiet, since, just like a forced air furnace, it will be shoving large amounts of air through the ducts. Putting that in the mechanical closet seems unavoidable if we will be using the old forced air ducts for air conditioning. They all converge on the mechanical closet because that is where the old forced air furnace was, though the ducts that were under the house have been removed and will probably need to be replaced.

I also asked Forrest if we could connect the air conditioning to a ventilation system with a heat exchanger. This would allow us to get fresh air into the house in summer through the air conditioning rather than opening the windows or running the HRV. He said that this typically isn't done, that the warm air return for the squirrel cage blower on the air conditioning comes from within the house, just as with a forced air furnace. In fact, the air conditioning (or forced air furnace if you have that) and the HRV are two separate sets of ventilation ducts. Somehow, one would think that somebody would have been smart enough to combine the two.

I continue to be amazed about the lack of efficiency in planning HVAC (heating, ventilation, and air conditioning) systems. Stuff that seems obvious to me as an engineer with a systems orientation never seems to have crossed the minds of the people who designed these systems. Every function is in a separate box. It is no wonder that over 40% of the energy in this country is used by buildings. Without proper integration of these systems, there is redundant energy use. For example, the squirrel cage blower on a forced air furnace and the HRV system are essentially doing the same thing: pushing conditioned air through ducts. Why not combine them, and run the cold air return through a heat exchanger on the furnace and out, and draw in outside air through the heat exchange and into the furnace?

Anyway, we've told Forrest to move ahead with the geothermal planning. We signed the design contract two weeks ago, but put it on hold pending an opportunity to experience how much noise an HRV system really makes. This means the final design will be pushed out by at least two weeks (and if we are lucky, only two weeks), meaning the start date is likely to be late June. Four months puts us into October. If the project is delayed (as usually in is the case in my experience) we could end up moving back in around Christmas. Considering we are planning on living in the back bedroom and also mostly outside during the summer, things could get a little tight come October when the weather starts to get cold again.

Monday, April 19, 2010

One Slice of Bread

Today I got a letter from PG&E telling me that they had decided how much they will pay me for the extra power my solar PV system generates, above what I use, starting next year. A couple months ago they sent a letter saying that they would start paying their net metering customers in 2011 at the annual true-up date. Up until this year, our solar PV system has been generating between $30-$134 more in credit than our house consumes. We kind of viewed at as our contribution to greening the planet since it hasn't been all that much.

The house isn't carbon neutral, though, we use around 1000 kwh/year more power from the grid than we generate. The difference is that we generate more power during the summer in the afternoon and evening than we do during the winter and in the morning. Due to time of day metering, PG&E pays us around $0.30/kwh for summer solar-generated peak power but only charges us around $0.09 for offpeak and winter power. It's a pretty good deal for us all things considered, though it wouldn't be if we had to use air conditioning during week days in the summer. We get the favorable rate because the folks in the Central Valley need to have their air conditioners on all day. So they use more power during the peak.

In their letter, PG&E proposes to pay its net metering customers $0.08/kwh for credit they incur above what they use. They claim this is consistent with the California Public Utilities Commission mandate in AB 920 (the law that requires net metering customers to be compensated for unused credit they incur) requiring the compensation to "set the rate for generation, including renewable characteristics, without shifting costs to other customers". I have a bit of trouble seeing how their math works out. If the power is worth $0.30/kwh to them in the summer, then how does it suddenly become worth only $0.08/kwh when they need to pay me hard money for it instead of trade? It's not like they don't have the information in their billing systems about when I generate the power, they could easily prorate the reimbursement based on time of use metering, just like they do with the cost.

The larger issue here of course is that such measly reimbursement rates aren't likely to encourage homeowners or businesses to install more solar. But this has been consistent with PG&E's position all along. The reimbursement rates quoted in their tenders for renewable energy systems over 1 mw a few years ago were similarly unattractive for investors, and they were fixed for 20 years. Contrast this with Germany and Spain, where feed-in tariffs for renewable power 3-4x fossil-generated power, set for 30 years have seen an explosion of investment in renewable systems. The net metering reimbursements are a kind of feed-in tariff, but not a particularly attractive one for individual investors, such as myself, who would like to maximize our solar generating potential but also earn some money on it. PG&E has been happy to provide net metering in trade, but when it comes to paying real money for distributed, small-scale power generation, well, that's another story.

I probably shouldn't complain, since the credit is actually just a mathematical construct due to PG&E's tariff structure. In the spirit of "half a loaf is better than none", I guess I'll take this slice of bread they're offering with gratitude, and hope the State Legislature and PG&E figures out some other way to encourage more solar.

Monday, April 12, 2010


Last week on Wed. we had a meeting with Forrest, our architect, to discuss the geothermal design contract. The contract had a lot of assumptions about our situation that weren't true, but Forrest said that his experience with the company was generally good, except for the design contracts. They tended to do this - put lots of irrelevant stuff in the contract - just to make it look more precise, though, actually, since it didn't correspond to our situation, it made the contract look inaccurate. We decided to take his word for it and go ahead with the design.

Later in the meeting, we reviewed a list of items that I have been accumulating. One of them involved soundproofing the geothermal heat pump and HRV system to ensure that they do not generate a lot of noise. Forrest told us that the HRV systems were, in fact, noisy but that there were measures, such as bending the pipe 90 degrees at the vent, to reduce propagation of noise from the HRV unit to the vent, although sometimes this couldn't be done. HRVs are mechanical ventilation and anybody who works in an office building knows what that sounds like. Basically you are working with the sound of a fan running in the ceiling all day as the accompaniment to your creative thoughts. Forced air heating sounds the same way.

Our house is particularly susceptible to noise, since it was built in the 1970's and there is nothing put into the structure to inhibit vibrations from one part of the house - say, the running fridge in the kitchen downstairs - from propagating to another - say, my office upstairs. When we had radiant heat put in a few years ago, we were astounded how quiet the house became in winter. It's not that you can't hear anything, the furnace still makes a low frying noise from the burning gas, it is just much quieter than having a squirrel cage blower whaling away in the mechanical closet, and the sound of the air whooshing out the vents. There's also the almost inaudible sound of the solar hot water pumps usually in the afternoon of sunny days, and, of course the fridge. But all these add up to very little noise, and the noise is also intermittent. With tightly insulated houses, the HRV system must be on all the time, otherwise the air quality inside the house suffers.

I found this a little hard to understand, since the German Passivhaus standard requires HRV. Passivhaueser (in German, "passive houses") are basically so tightly insulated that they require no supplemental heating beyond that from the appliances (like the fridge) and people within them, even in the cold German winters. An HRV system takes fresh and possibly cold air from outside, circulates it through a heat exchanger with stale air from inside on the other side of the heat exchanger, and exhausts the fresh air into the house and the stale air to outside. In this way, the occupants get fresh air but the heat is retained. Our insulation would not be that tight, since we have the solarium on the back that probably leaks heat and air, and also, we are not reinsulating the master suite nor one wall in the kitchen, but nevertheless, the amount of insulation we are putting in is enough that it could cut down on the amount of air infiltration sufficiently to allow air quality to suffer. We already have a problem with cooking odors lingering into the next day.

Now Germans are particular about noise in their houses. Even regular German houses are very solidly built in comparison to American houses, usually from ceramic bricks shaped like cement blocks, and they have heating systems that run on oil or gas that either use radiant heat as we do or radiators under windows. American houses are flimsy in comparison. All this mass makes for a very quiet house indeed, very little traffic noise penetrates. So I found it hard to believe that HRV systems could be noisy, the Germans who are now building lots of Passivhaueser, would never stand for it.

Naturally, I went on line to try to figure out what the problem was. In particular, I wanted to find out how much noise HRV systems emitted. The specs for the unit Forrest recommended had no noise rating. But - surprise! - the same thing was true of every single unit manufactured in the US or Canada that I looked at (and I checked 10)! The only unit sold it the US that had a noise rating was the Panasonic WhisperQuiet(tm), which is made in Japan. The WhisperQuiet is actually a bathroom ventilator, because it exhausts directly out of the unit rather than through a duct, so it is unsuitable for our situation, but the noise rating (though in an unusual measurement) was quite good.

Even more surprisingly, every single unit manufactured in Germany and sold in the other countries of the EU had a noise rating on it! The quietest I found were products manufactured by Paul Lueftung. There are various models, but the noise rating ran from 18 db to around 33 db. This is about the amount of noise in a quiet room, and these units are in fact used in Passivhaueser. Products from other companies typically started at 35 db. Unfortunately, the units conform to the European power standard - 230V/50Hz. In the US, we can get 220V which is probably OK, but 60Hz which might be a problem for an AC motor. The units may have DC motors and a power supply, in which case, we could convert them to our power standard. I need to look into this as a possibility.

It seems rather strange that the US manufactured products don't come with a noise rating. Don't Americans care about noise? I guess not since they put up with noisy forced air heating and noisy ventilation in offices, or maybe the sound of all that electricity being used makes people feel like Progress is happening. But I suspect the answer is much simpler: the German government requires manufacturers to include noise in their technical specs whereas the American government doesn't. Guv'ment regulation! The German technical specifications were also considerably more complete and prominently available on the manufacturer's web sites. In several cases, it was difficult to find the American manufacturer's specs, and they were quite skimpy, for example, the noise rating was listed as "quiet".  Of course, your "quiet" might be my "noisy", a db rating is much more objective.

I also looked briefly into noise from geothermal heat pumps, there the situation was the same. Lots of web sites talked about how little noise they generated outside, in comparison to air source heat pumps, but nothing about the actual noise generated by the heat pump itself. I figure that there are three components to noise from the heat pump: the pump circulating the heat transfer fluid into the ground and out, the compressor, and the forced air system (if the system is forced air). On heat mode, our system won't have the latter since we use radiant heat, but we would have the first two. On air conditioning mode, of course, we would have to put up with all three, but there is nothing we can do about that, it is not possible to use a radiant heat system for cooling. I figure that the compressor can't be much noisier than a fridge and the heat transfer fluid pump should be about the same as the solar hot water pumps, but then who knows? A fridge we got in our old house was so noisy that we got rid of it after a couple years, we could not afford to do that with a heat pump. The heat pump will probably have to be American manufactured because the electrical system is probably too complicated to convert,  so it could be bad.

Anyway, we asked Forrest to hold off on the geothermal design and the HRV design until we get more clarity about this issue. In the worst case (i.e. we can't get a quiet HRV system), we can back off the insulation and  just do under the floor (where the current fiberglass batting causes lots of radiant heat to leak in to the crawlspace) and on the central hallway ceiling, which must be replaced due to cracking, then we probably don't need HRV.  As for the geothermal,  maybe we could mount the compressor and heat transfer loop pump in the garage, and the heat exchanger in the mechanical closet. Or possibly get some kind of soundproofing under the compressor so it doesn't shake the floor.