Sie müssen Brand Viagra nur bei derviagra apothekeViagra Brand ist für jene Patienten nicht angezeigt, die eine andere Medizin gegen

Cialis is cheaper than brand pills, and you can always afford normal treatmentcialis onlineCialis online simply place your order, use your credit card to pay for your pillscialistaking erection pills to support your compromised erectile function (you will not have to take Cialis for the rest of your life.There is only one place to play from Online Casinos.casinoPlay Online Slots.Usually the recommended dose is 50 mg Viagra.ViagraViagra 100mg

Increasing our Solar Thermal System vs. Gas Boiler Backup

by Chad Ludeman on November 7, 2008 · 20 comments

in Building Science,HVAC,solar

Problem Statement

The high efficiency Munchkin gas boiler is more expensive to install (>$3,500) than budgeted as both a backup to the Schuco Slimline II-80 solar thermal system spec’ed out for domestic hot water and a sole source of heat to our hydronic radiant heating system (more on these mechanicals here). Installing gas service to the house will also cost an additional $2,000 in permitting fees and additional plumbing costs to run the line inside the house. The high efficiency (97%) of the gas boiler is needed to accomplish a HERS rating of 52 that enables the 100K House to achieve a LEED Platinum rating. Electric alternatives to heating water are not nearly as efficient overall and will dramatically increase our HERS score.


If we increase our solar thermal system parameters by two more 25 square foot solar panels and an additional 80 gallon storage tank with integrated electric backup heater, we will be able to eliminate the gas boiler while reaching the same efficiency as the gas boiler backup design without increasing overall cost. This design has the potential to be lower in overall cost with the eliminating of any gas service run to the homes at all.

Key Variables

The big hurdle in switching to all electric water heating while still achieving the same HERS rating is the difference in the source to site multiplier between gas and electric. What the heck does this mean? Basically, since the US is so lousy at efficiently generating and transporting electric power to our homes, the HERS rating system multiplies the power used by electric appliances by 3.16 to compensate for the roughly 30% efficiency level we are generating electric at currently. For gas, this multiplier is only 1.02. So, if we are going to replace our gas boiler with an electric backup, we must be three times as efficient in terms of total power used.

We have calculated that we will need to compensate for roughly 67% of our radiant heating demand in the winter with increased capacity in our solar thermal system. This leaves us with just over 2,000 kWh’s of supplementary electric backup heat for the entire year.

Yesterday a three man team from local solar experts, Solaris Energy, sat down with us for a marathon meeting to try and determine if our goals above are possible. We have a proposed design and will be sending it off shortly to the fine engineers at Schuco to see if we are in the ballpark or totally off base. Stay tuned for the update and lots more math.

If you enjoyed reading this post I can promise you'll love our new writing over at Postgreen Homes. Yeah, we know that's the same thing your favorite band said and their new album is nowhere near as good as their early stuff, but seriously, we are actually still getting better.

There also isn't much conversation to be had here . . . at least not with us. So come on over to the Postgreen Homes Blog and tell us what you think of our new(ish) digs and crazy ideas. We will be sure to tell you what we think of your opinion.

{ 1 trackback }

Your Questions About New Modern House Plans | Home Design News
September 23, 2011 at 9:02 pm

{ 19 comments… read them below or add one }

1 chad November 7, 2008 at 8:13 am

I wanted to point out that one reader, Alex, already commented on this issue from one of our Twitter remarks. He is certainly welcome to re-comment here, but his comment can also be viewed at the following link –

2 Rob November 7, 2008 at 9:58 am

This is awesome that you are looking into this level of detail for the heating system, something most dont do. But I wonder if you arent making a huge mistake by not putting gas in this house? I just think that if we single source our current fuel needs, in the future we may be up the creek paying outrageous prices for that fuel supply. Gas pricing this past summer anyone?

Could you design all of this in such a way as to have it be gas for now, while remaining flexible enough (and with enough space) for additional solar thermal in the future?

Also doesn’t it make sense to use the most fuel efficient source, rather than our current inefficient power grid? Of course I guess the ideal would be to have additional solar thermal with PV’s providing the power. :)

3 chad November 7, 2008 at 11:40 am

Your last sentence is the idea Rob. We plan to leave enough roof area that the homeowner could install a PV array to make the house net zero energy in the future if they so desired. Incentives are coming back to PA soon and improving next year at the federal level, so this will be a viable option in the near future.

If we spend thousands to bring in gas and install an expensive gas system, it doesn’t make sense for us to encourage the homeowner to tear it out and convert in the future. We are putting so much time into the mechanicals and envelope because these are not the things that are easy to upgrade in the future…

4 Kevin D November 7, 2008 at 7:42 pm

Maybe you considered it, but think about taking the Schuco system money, and put it toward PV.

The reason I suggest this is because of experimental results from similar homes in the field. See, summertime is when a lot of solar can be collected. Space heat is needed in the winter on days when there isn’t any solar to be had.

One of these experimental homes had a solar thermal yearly efficiency of only 7% because of this supply/load mismatch, even though the collector efficiency is 70%. PV system efficiency is constant at a paltry 12% but cranks it out ALL summer and spins the electric meter backwards while your neighbors use your excess collection. With PV, nobody needs to store solar energy. With solar thermal, you have to store it and those tanks eat up expensive real estate inside a home without a basement.

Since you will be living in the house for at least two years, you may want to delay the solar investment. Pennsylvania may implement PV incentives and PV prices should come down. Therefore, you could sacrifice some LEED points now, but get them back in a few years at a lower price.

5 chad November 7, 2008 at 8:10 pm

Kevin – You make some good points. Honestly, I am skeptical that we can get enough insolation to hit our new target efficiency for the radiant system in the winter. In the summer, we will have a tremendous amount of excess heat which is a bit irritating.

This all comes down to economics though. The bottom line is that it is much more cost effective to heat water with solar thermal than it is PV. That is what we are all about in the 100K since there is no AC.

Additionally, we are not talking about extra cost here, rather substituting the cost of gas and the boiler for extra solar thermal. Since we already have all of the guts and controllers designed in, we simply have extra panels and an extra water heater. The additional labor will be minimal as well. For the extra cost we will incur upgrading the solar thermal, we wouldn’t even be able to purchase a DC to AC converter for a PV system, let alone the expensive panels that go with it.

You are right. Incentives will return to PA and then it will be more viable. While we are working on this design, we are racking our brains for the best design in the next homes that will allow us to offset 100% of the HVAC energy demand on our budget. Offsetting the rest of the appliances and lighting at an additional cost will then be up to the homeowner…

Keep up the good comments here. This is a tough issue.

6 Goran December 31, 2008 at 3:05 pm

Are 80 gallon water tanks the most cost effective heat stores?

Is anyone out there using double slabs, one on top of the other? The larger, lower slab, could be used for longer term heat storage, and could be heated well above 70F. It would be lightly insulated from the thinner upper slab, which would be used for radient heating.

The much larger lower thermal store could bridge winter needs during several cold weeks.

The concrete and additional thin layer of insulation should be cheap enough, but the double PEX plumbing might run up the cost.

Or how about a thin radient slab and an insulated, water filled heat store below the house. Saves on PEX, but some extra cost needed to construct the tank.

Water has 4 times the specific heat capacity of concrete, with around 1/3 the density so an 8x8x8′ cube of water should have the same heat capacity as a 16″ thick, 500 sf concrete slab, yet would only need 320 sf feet of additional heavy insulation. A shallower tank would need even less: for example: a 13x13x3 tank would need less than 160 sf of added insulation, and have the same volume as an 8′ cube.

According to the info in the “shallow insulated concrete foundation” blog entry, there’s a chance that this will be able to bridge winter heating needs using summer reserves. They cited home temps dropping 1 deg per day, during the 11 day winter power outage, with an 8″ slab, in a well insulated home.

A water tank could be heated to over 100F, which together with its double heat capacity, could provide 60 days (100-70 = 30 * 2 = 60) of heating during winter, without additional input. And it has the added advantage of:
- allowing setback thermometers to control radient heat from a thin radient floor, saving energy.
- allowing a warmer radient floor temp for added foot comfort. If the primary heat store is your floor, it must be kept within a couple deg of the air temp, which makes it feel clammy.
- eliminating need for PEX plumbing in the primary heat store, should reduce cost as compared to a double slab.
- reduce concrete needed in primary slab. Saves a little money, but this is offset by cost of additional excavation, and casting the concrete tank.

Anyhow, its fun hand waving.

7 Goran December 31, 2008 at 3:26 pm

While we’re hand waving, why not have two insulated tanks, one for hot water for heating, and one with cold water for cooling. All that’s needed is effective insulation that’s cheap enough, and adequate control systems. During a bright winter day, pump water from the hot tank through the solar panels to pick up additional heat, during the night, pump water from the cold tank through the same panels to cool down the cold tank. It might even be possible to get the night time cold cycle running using thermal siphoning, so that backup power, and a seperate anti-freeze loop and heat exchange aren’t needed. Daytime PV could power the pump for the hot cycle.

8 Goran December 31, 2008 at 9:31 pm

Correction. The Legalett site said they saw a 2-3C slab temp drop per day, not 1F, at 20F outside temp, so a 100F 512 cu ft water tank could be expected to provide about 2 weeks of heat, not 2 months, in a typical well insulated home.

9 Goran January 1, 2009 at 11:37 pm

Did some research and this topic (seasonal heat storage) has been kicked around for decades. Building envelope is the key. Anything you do after that is icing on the cake. If the cake is bad, its hard to fix it with icing.

10 Kevin D January 2, 2009 at 1:45 am

For the near future, annual net zero energy cost is a worthy goal. This year in CO at least, the utility is now required to rebate cash if your PV system generates more electricity than you use. The net metering laws nationwide require them to pay the homeowner/investor full retail price for what they put on the grid.

The Smart Grid will increase the amount that is paid per kwh to these folks, because PV electricity is generated during expensive peak periods. Like on hot, sunny, summer afternoons.

Annual net zero energy cost homes can be easy, simple, and cheap. More on this:

H4H built one in Arvada

11 tom toolbag January 4, 2009 at 12:11 pm

WOW! I have been browsing this site for about 4-5 hours now, and found some things that I can relate too. There are a lot of ideas and info here, what a breath of fresh air!
I found another posting refering to a design with 2 envelopes, or 2 walls, by zero energy design. I built a house like this in 1985 for my parents and that design works very well. Goran brought up the idea of using water as a heat sink, we used river-rock. The house had a basement, and there was a pit roughly 20′x 10′ full of river-rock with ceramic tile above it. The south side had casement windows with a “sunroom”, and the heat would transfer into the rock, and when the temperature changed/inverted it would rise up into the air space(the space between the exterior and interior walls). I thought that water could be used also, but how to cover or transfer heat to it directly. This worked really well, and other than the three concrete walls of the pit, it was fairly cheap. They wanted a basement anyway, and in that region(just outside Moline, Il.)you gain ambient temps from one also. The house had NO furnace or a/c, 50g elect. w/h, electric baseboard heat with a stat in each room. This house cost $45.00 p/m to heat, and never got above 68-69 degrees in the summer. They had planned on putting thermal blankets(curtains) on the windows but never got around to it. The biggest problem was fresh air and humidity. My step-dad was too cheap to pay for a hrv/erv, but they were pretty expensive also then. Ironically, he later had a job as a hvac salesman and could have got one at cost and he wouldn’t part with the money. This house was built(with 2 1/2 acres) for $50,000.00 in 85, so that’s an idea how costly it was. When they sold after 13 years, it sold in 4 days for about $262,000.00. I wanted to buy it but couln’t match that offer……besides the fact that Icould build it for a lot less!
I have designed a house with same wall system(it’s called an envelope house) but a MAJOR obstacle is sizing the hvac system. It will be built off-grid, so relying on electric is not an option. Finding systems small enough or properly sized baffles building departments and they throw a wrench in the system. A hrv/erv system would ALMOST totally supply the needs, but they won’t let that fly. Back-up after back-up systems is all they know.
Anyway, I would rather spend more money on the walls or envelopes than mechanicals. Walls don’t wear out, or need repairs.

12 chad January 5, 2009 at 3:49 pm

Tom – Great comment. Thanks for the insight into the envelope design. We are focusing on the Passive House concept of super-insulation for our next project, but the double envelope is still bouncing around in my head. I think a cool multi-family could be built with the concept.

13 chad January 5, 2009 at 3:53 pm

Goran – Great comments. I couldn’t agree more with your stressing the importance of the envelope. That’s the key to an energy efficient home, period IMHO.

Check out our post a while back on an Alternate Solar Thermal System for more insight into what you are touching on in your comments.

14 tom toolbag January 5, 2009 at 8:40 pm

This type of building works well but could use some improvements. The south facing casement windows usually had heavy condensation on them in the winter. This was due to the design and lack of completeness of the design. the exterior walls were insulated but the ceiling(underside of the roof)wasn’t. It had soffitt vents and a continuous ridge vent and I think that was where the problem was. I think we should have insulated the roof, and either sheeted the underside of the trusses(we didn’t) and used a white or light color(we used dark brown) shingles so as to keep the exterior walls and air space complete and moisture free. It would be like putting a ziplock sandwich bag inside of a ziplock freezer bag, then a spacer on the outside of the freezer bag under the roofing material. The condensation would collect on the glass, but moisture had to be in the air for it to collect somewhere(the glass). No humidity, no condensation. Knowing what I know now(I was 18 then and had no knowledge or experience then) I would put the vapor barrior on the exterior side of the outside wall, create an air space under the (white)roofing, such as a fir strip, and then also on the exterior side of the interior walls and ceiling. I would use spray-in foam insulation on the exterior walls and roof, 1/4″ sheeting on the exterior of the interior walls, 1″ foam board on the interior of the interior walls with 1″-2″ of shot-crete on all the walls instead of drywall. I think drywall is too labor and manufacturing intensive now and has outlived it’s greatest benefits by far. My theory is if you can control moisture, contain heat/repel heat with the exterior wall, and hot goes to cold, the interior wall does not have to be insulated as much(less heat loss or transfer) if the temp on the other side is nearly the same. You would need a hrv to cycle in fresh air to the living area, and erv to cycle air into and remove humidity in the air space. My plan for this was to build a house like this, get it up fast using the types of technology available now, let it sit and moniter the conditions for needs throught the weather cycles. In other words, build in early spring, let it sit through the summer and winter seasons to see what was ACTUALY needed for cooling/humidity control, and how much heat is needed. The overall timespan would be 12 mos min plus build time. All hvac systems would be broken down into: cool/humidity removal, and heat humidity addition. That takes the calculations and precision out of the process. You would need systems that could be upgraded in increments to make this work. My reasoning is this: if you take a 24 hour period and chart the temps on it you want it to be as strightline as possible. There should be no peaks or valleys, like when a system turns on and off. Why have a furnace or a/c system that can change 5-10 degrees of temp real fast, when a few tiny systems could run more often to maitain a 1-2 degree range. An example is a whole house boiler system for floor radient heating. If there is a manifold and electronic controls for zoning the house(some areas on/some off) then a boiler big enough for the whole house wouldn’t be needed. I’m imaging something the size of a tabletop gas grill for different zones running sporadically. Another idea is why not have circulation pumps that can reverse the flow from the boiler instead of heating the system from one end. My idea is to use an oversized pilot light sized flame to heat the water instead of a large boiler type to get there real fast. One big problem is that there aren’t any systems like this on the market. My idea of letting a house sit for one year is the only way I know of to properly size hvac systems and still (hopefully) satisfy building inspectors/departments. A conventionally built home might take 3-6 mos to build, so in my situation losing 6 mos is worth it, because time is cheaper than expensive systems, especially if they aren’t needed. It’s the right tool for the right job mentality.

Here’s some other points to ponder:

why put a concrete floor in the basement? With a crawlspace, concrete isn’t needed. It’s a lot of overkill to use just as a floor unless you need it for massive weight such as a hot-tub.

why design a roof to carry a certain load instead of designing one to carry no load?

why have a big bathroom and put the toilet in a clost-sized room?

why use an exhaust fan to remove moisture from the whole bathroom instead of enclosing the bath/shower and removing it at it’s source?

why use (labor-intensive)concrete forms for a foundation when icf’s could be used to alleviate covering the same area 3 times, 1- to form, 2- to strip, 3- to insulate?

why use drywall with the 2-3 finish coats if you could spray shotcrete on in 1?

why put a washer and dryer in the basement when you dress/undress in the bedroom or bathroom that isn’t in the basement?

I’ve had numerous discussions about these things with people ranging from architects to carpenters, and noone has has to this date given me any adequate answers. Processes and materials are ALWAYS more predictable and reasonable than people. I always teach anyone that works for me to work smart not hard, use the right tool for the right job, and to tell me what you can’t do as opposed to what you can…I’ll figure that out soon enough. The people that are going to read this are probably the only ones to relate or know what I mean, or are curious or have the initaitve to want to make the changes that the building industry needs. The mentality of doing something even if it’s wrong, or just because that’s the way we’ve always done it, doesn’t fly anymore. Change is always resisted, but it’s also inevitible.

15 chad January 5, 2009 at 10:04 pm

Excellent points. Tell me more about these shot-crete walls you speak of. I like the sound of it.

16 tom toolbag January 5, 2009 at 11:19 pm

I stumbled across a website called Solarcrete. They have a wall system that uses rebar and foam covered in spray-on concrete. A lot of swimming pools use spray on concrete, and molded /formed foam covered with spray on concrete is used for decorative rocks in indoor fountains. At a certain thickness, it is fire rated(I think) and dye could be mixed in to act as a color base, like a primer. I don’t know how it could be inspected other than to have a building inspector on-site when it is sprayed on, maybe there is some sort of depth gauge that they tack on to show the finish depth and then you snap it off. The Solarcrete company is about 45min. from me so I would be a moron not to see their system going up and it’s finish. There is also a link to a pv company named Atlantis Energy, they have a combined heat and power system that I’ve been thinking about for 5-10 years(go figure, somebody beat me to it). It’s a pv flat roof tile over a pex tubing layout for solar thermal. I couldn’t give you any specs because I haven’t contacted them or studied their info. I did e-mail Solarcrete to see if that system could be used below-grade and they just gave me a basic formal response without any answers. I guess that I didn’t come across like a sale, just a sight-seer.

17 Kris December 4, 2010 at 2:35 am

Increasing the size of your solar thermal array without a significant increase in ways to store the heat for when you need it seems like a waste of money. Most people using solar thermal to supply significant space heating use water tanks that are much larger than the typical hot water heater and/or sand beds to store heat during the sunny months for use during cloudy times. I don’t know what PA is like but in MN we need to have a way to store the solar energy from July/August for use during the typically cloudy November/December. By January it is usually very sunny again. A word of caution to people planning for solar thermal systems, make sure you do your homework. There have been a lot of poorly designed systems installed in the past 30 years. I am a huge fan of solar thermal and we are going to depend on it for most of our heating but it has taken a lot of careful planning/design. I’ll be interested in continuing to read about what you ultimately decided to do and how it has worked out for you.

18 Chad Ludeman December 4, 2010 at 7:20 am

Kris – What do you do with your excess solar heat during the summer months when you are getting much more heat gain than the winter?

19 Kris December 4, 2010 at 7:26 pm

Since we had to excavate 4 feet down for footings, we just had them scoop out the center. We then insulated the bottom and sides (4″ foam), filled it with sand and 2 layers of Pex and then capped it with 4″ foam (we call it our thermal vault). The slab will be poured on top. We will pump heat into it in the summer months and then pull it out at the start of winter. We have a small basement area to act as utility space and it has 2 large tanks we have repurposed (one was an old dairy tank and we were able to pick them up for cheap) and will be outfitting with copper heating coils. This will act as short term storage during the colder months when we want to take advantage of a sunny day and store away heat for the next cloudy days.

Bob Ramlow in Wisconsin has done a lot of houses using the sand bed system except his have been uninsulated on top so by September or October heat starts to just passively transfer up into tthe living space which can result in overheating (which is usually solved by opening windows or turning on AC which seems crazy to me). We want to have better control of the heat and we won’t have any AC in the house so the thermal vault concept was much more appealing.

We are just getting blog up and running (only about 3 posts) but I’ll try to post a link later. We certainly aren’t as trim a budget as you, but then again we are building what will hopefully be our final house, our dream house. We are putting lots of sweat equity into it.

Leave a Comment

Previous post:

Next post: