I have just finished up plans for a home I am building about an hour north of Detroit. The house will be 2900sq-ft two story home with a 2 story great room on a "for now" unfinished walk-out basement. The plan currently is to build on superior xi foundation walls and 6.5 OSB SIPs for exterior walls and a traditional truss roof with blown in attic insulation. Windows will have a U .26 and a SHGC of .31 The home will face north. I have used the BEopt software to model the home and I used what I am familiar with, a forced air heating and cooling system. BEopt calculated the heating @ 58kBTU/hr and cooling at 25kBTU/hr. Do these numbers seem accurate? The property has natural gas. I am open minded currently on HVAC design, but feel a bit overwhelmed with all the options and such (windows were bad enough). I am looking for the best bang for my buck to tackle this issue. Is a high efficiency gas furnace coupled with a seer 13 AC unit going to be tough to beat? What other systems and configurations should I seriously consider? Thanks Fred

What HVAC strategy will provide the best ROI largely depends on the cost of fuel in your area during the 20 years or so that you will operate it before replacing it with another strategy. I hope and expect that renewable electricity will eventually become the future fuel of choice.

I would think that a ductless mini split strategy having a high COP would be hard to beat for both cooling and heating if you are okay with moving air. If you want to avoid moving air, you might want to consider hydronic radiant cooling and heating using a heat pump having a high COP.

Once you have the total heat loss in BTU/Hour-Degrees F for your residence, you can use our integrated performance software to assess the various HVAC strategies given your cooling/heating degree days and your local cost of fuel:

Borst Integrated Cooling System Performance Software

Borst Integrated Heating System Performance Software

Is that something BEopt can calculate, the heat loss per hr? I showed my better half the mini ductless splits and she does not like the look of them and would rather just have registers. If I were to do hydronic radiant heat in the floor, I would still need a separate system for cooling correct? What is the experience on here with a system like the unico for cooling? Thanks Fred

I am not familiar with BEopt, but you indicated that it calculated 58,000 BTU/Hour for heating and 25,000 BTU/Hour for cooling. Since you must already know your indoor/outdoor design temperatures (e.g., 70F/10F and 75F/100F) to obtain this information, you can just divide these BTU/Hour values by your design temperature difference values (e.g., 60F and 25F) to obtain the heat loss and heat gain values in BTU/Hour-Degrees F (e.g., 967 and 1000 BTU/Hour-Degrees F) enabling you to then use the integrated performance software to assess the various HVAC strategies.

Yes, I am not particularly fond of how mini splits look either. Actually, to be perfectly honest, I very much dislike them aesthetically. They seem like obtrusive dust collectors to me. Nevertheless, they are very simple to install and they are extremely efficient (e.g., perhaps 2-3 times more efficient than any gas furnace). So at some point they become very attractive!

Hydronic radiant can be used for both heating and cooling. Perhaps see this thread for more information with regard to radiant cooling:

Radiant Cooling

Fred,

If you have natural gas available, it is typically a very cost effective way to heat. Plus the ducting for a hot-air furnace provides an easy way to add whole house air conditioning, air filtering, heat-recovery ventilation, humidification, etc.

sailawayrb mentions that the efficiency of minisplits is 2 or 3 times that of a gas furnace. This may be true under not-too-cold conditions. However, from both an energy and cost standpoint, it is appropriate to do an analysis back to the source of the energy. So to generate the electricity and to account for losses in the lines, it takes 2 or 3 times the amount of natural gas energy to generate the electrical energy required to run the minisplits, unless you are going to put solar PV panels on your roof. Therefore, from a source energy standpoint, there is not dramatic advantage of using minisplits compared to natural gas furnaces.

Michigan coal-burning plants accounted for 66% of the electricity generated in Michigan in 2009 (http://www.dleg.state.mi.us/mpsc/reports/energy/energyoverview/). Certainly burning natural gas for heating is cleaner to the air than burning coal to generate electricity to run a minisplit. Coal produces twice the carbon dioxide as natural gas, twice the nitric oxide, and large amounts of mercury and other heavy metals, fly ash, etc. that are not produced at all burning natural gas. Natural gas is relatively clean... solar is much better and is very cost effective in my part of the country.

Fred,

I would also like to mention that I was surprised at your choice of low solar heat gain windows for your new house, SHGC = 0.31. According to my calculations for that general area (http://www.residentialenergylaboratory.com/window_codes.html), you could do slightly better with higher solar heat gain windows, even though the U-factor is slightly higher. Anyway, since you are already set up in BEopt, I would test out high solar gain windows, at least on the south side, and compare with your current design.

Lee/Sailawayrb.

Thanks for the replies. one quick question, how do I get paragraphs and line breaks, cant figure out the formatting?

I think what sail is saying is in the near future solar renewable energy will become much more of a player and I tend to agree and will take steps that I could add panels on my southern facing roof if in fact it does become a little more attractive, but we cant get over the unattractiveness of the minisplits.

I actually just got an email back from the window folks and the windows (Sunrise) are actually are 0.24 U and 0.21 SHGC. This is 12 layers of low e on both panes for the 2016 energy star compliance. I would think that would be fine for N, E and W windows, but for south facing windows I would think I would want that number to be at least over .4 SHGC even if it hurts the overall u value. Could someone recommend a coating from cardinal that I can inquire about?

I also forgot to mention the great room will have a high efficiency wood burning insert. Something like a quadra-fire 7100. I have about 10 plus years of standing dead ash trees (emerald ash bore) that will feed the fireplace.

Thanks
Fred

LoE-180 is one of the Cardinal glass coatings that gives high solar gain. You can check their catalog for SHGC specs and other options. BEopt will handle the analysis for whatever windows you want to compare. (Cardinal glass will give you specs for the insulated glass unit (IGU) only, so you have to estimate specs for the overall window.)

The solar PV system that I have is already more than cost competitive with utility-provided electricity. My cost amortized over 25 years is $0.064/kWh, and the utility charges $0.118/kWh (http://www.residentialenergylaboratory.com/comparison_of_pv_systems.html). Looked at another way, after 9 years my system is paid for, and I get free electricity for the next 16 years of the 25-year guaranteed lifetime of the system. If I had a larger system than the 3.15 kW that I do have, I could run my heating system off of it, but I use a natural gas furnace instead. It would only make sense to see if you can include a roof design that would provide a good orientation for solar panels.

The problem with forced air in a 2 story room is the majority of the hot air you pump into the room pretty quickly travels over your head and just sets there against ceiling walls and windows, it's heat energy percolating thru your envelopes insulation. Now you can put a return up near the top to take and re-pump that warm air back thru the system more frequently, but pumping air costs money... IMO a large volume room is where radiant really shines.

The problem with solar is being able to provide enough useable energy to meet a large percentage of your needs. 58,000 BTU/HR at a 2.5:1 COP heat pump efficiency still equates to 6.8KW/HR of electric... If it gets really cold out and the heat pump reverts to pure electric mode, that is 17KW/HR or an equivelent ammount of NG after furnace/boiler efficiency is factored in...

IMO the key to using solar(or any other renewable) is to get your demand below a reasonable/achieavable supply. In this case, carefull air control, good windows and insulation are your friends. This is true regardless of the energy source. Insulation and windows have a known cost today. What will a KW or Therm of NG cost you next year or 10 years down the road? I am thinking it will not be less than you are paying now...

A heat load of 58,000 BTU/hr for a 2900' room is on the high side even for a code-min 2900' house. Your design-temps haven't been stated, but it seems CRAZY high for a high-R house. That's 20 BTU/hr per square foot of conditioned space. My sub-code 1923 vintage house doesn't hit that ratio until the outdoor temps are in negative double-digits.

The whole coal-fired power grid efficiency blah-blah is a total straw man argument. Coal is toast, dead, DONE- stick a fork in it! The grid-supply mix in 2009 isn't what it is in 2015, and isn't anything like what it will be over the lifecycle of a mini-split. Try this one on for size: A shiny-new combined cycle gas plant delivers about 50% efficiency from source fuel to load after grid losses. A cold climate mini-split running full-blast delivers a COP of about 1.8 at -25C/-13F, and much higher when its above +10F and modulating. Your worst-case fuel efficiency would then be 1.8 x 50% = 90%, and your average fuel-load efficiency would be north of 100%, were the grid supplied completely by combined cycle gas. But it isn't, at least not this week.

In 2015 nuclear + renewables + natural gas nearly outstripped coal which barely cleared the 50% mark in Michigan this year:

http://www.eia.gov/state/?sid=MI#tabs-4

It's unlikely coal's contribution will be above 50% in 2016, and even less likely that it'll be above 25% in 2025. The alternatives are too cheap, and keeping the low efficiency coal plants going makes no economic sense even without the Clean Power Plan.

Wind and solar are on an exponential growth track, now destined to continue since last week's vote to re-up the production tax credits for wind for several years, and the 30% tax credit for solar has been pushed out for another 3 years, followed by a slow step-down out to 2022 rather than a drop-dead date cliff. Both technologies have double-digit learning curves too, which means they are rapidly getting cheaper as installation volumes increase. New wind is already competitive with new gas in the midwest, but wind costs are falling, and gas pricing has nowhere to go but up from the current historical lows. Solar's learning curve is over 20%, and the recent-years doubling rate is less than 2 years (every 2 years it takes a greater than 20% price cut.) If you installed a mini-split today and assumed a lifecycle of 15 years, by the end of it's lifecycle solar will be the cheapest grid power source by a good margin.

But there's no mini-split solution that makes sense for a true heat load of 58,000 BTU/hr. Figure out where that heat is going, and fix the house design. A respectably high-R design (not super-insulated, just pretty-good, say 1.5x code performance) should come in under 10 BTU/hr per foot of conditioned space at +5F or whatever your 99% outside temperature is. Here's a short list of design temps used by ASHRAE. (For a code-min or better house, design to the 99th percentile temperature bin, not 99.6th.)

https://www.captiveaire.com/CatalogContent/Fans/Sup_MPU/doc/Winter_Summer_Design_Temps_US.pdf?v=17112015

Here another set from the ACCA:

https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf

I wish coal were dead, it kills a lot of people. Maybe in 20 years.

Consider ducted mini-split heat pumps, perhaps combined with some nat gas.

I think I need some more practice in BEopt. After playing around in it my heat load is now 66,000BTU/Hr. The heated square feet closely matches my plans and I do have some unfinished attic/storage rooms. The gable ends don't match up to my elevations and in the rendering one of the ends is open with no siding. Not sure if that is a glitch or is part of my problem? I was mainly focused on getting the square footage correct and room layouts. I wish I could post the screen shots of my elevations vs BEopt to see if that could be part of my problem.

Dead? Yes.

But buried and gone? Not yet.

The utilities have considerable sunk costs to recover, and are lobbying to keep some of those assets from being stranded too soon. But they will never build another coal fired plant, and most of the existing fleet will get early retirement rather than a life-extension.

But is coal sufficiently gone that heating with mini-splits in MI will be nicer to the planet than heating with condensing gas over the next 15 years? You bet!

Wind power has a lot of room to grow in MI with plenty of available wind resource (20-25 GW by most estimates, much of which could opearate at a capacity factor well north of 30%). And it's very economic- cheaper than most of the existing coal-fired capacity in that state. Just as Texas has gone from less than 1% to 18% of all power on the ERCOT grid sourced by wind in less than 10 years, Michigan can too, despite have less wind resources, now that the technology and prices have dramatically improved. And just as in Texas, rapid expansion of wind will eat into the capacity factors of the least-efficient / most expensive (= highest carb, dirtiest) coal plants fairly quickly. The Clean Power Plan hurdle was about as high as a painted stripe on the pavement for Michigan at the get go, and incrementally lower now that the PTC driving wind development has been extended.

The billion dollar carbon question is whether wind will eat nuclear power's lunch even more than thermal coal's, which isn't entirely clear. But it's not as if solar (on both sides of the meter) will be standing still during that time either. That party has barely gotten started, and has a potentially faster development ramp than wind where there is policy support from regulators.

I'll be surprised if coal holds more than a about a quarter of the power pie in MI in 10 years. It only took 5 years to drop from ~65% to ~50% as combined cycle gas ate it's lunch on efficiency, flexibility, and cost. Gas isn't going away, but it's competing with wind, and that competition is getting tougher every year. Wind can still make money when the LMP is slightly negative as long as the PTC is in place, and even when it expires it still breaks even at a price of about $2/Mwh, which is a huge money loser for anything that uses fuel.

In 20 years, who knows? There may still be a few coal plants operating in MI, but I wouldn't bet the farm on that.

Posted By Dana1 on 23 Dec 2015 03:02 PM
The whole coal-fired power grid efficiency blah-blah is a total straw man argument. Coal is toast, dead, DONE- stick a fork in it! The grid-supply mix in 2009 isn't what it is in 2015, and isn't anything like what it will be over the lifecycle of a mini-split. Try this one on for size: A shiny-new combined cycle gas plant delivers about 50% efficiency from source fuel to load after grid losses. A cold climate mini-split running full-blast delivers a COP of about 1.8 at -25C/-13F, and much higher when its above +10F and modulating. Your worst-case fuel efficiency would then be 1.8 x 50% = 90%, and your average fuel-load efficiency would be north of 100%, were the grid supplied completely by combined cycle gas. But it isn't, at least not this week.

Maybe in your fantasy world, coal is dead. But for those of us working in the real world, we look at the graph presented in your reference and it shows that electricity generation by coal in Michigan outstrips second place by more than a factor of two!

In your fantasy world, electricity is a clean energy source, but pull back the curtain and notice that coal dominates electricity production in the U.S., ahead of all other sources. The proportion of electricity generated by coal is dropping, and solar is gaining, but solar is only 0.4% while coal is 39% for the U.S. as a whole (https://www.eia.gov/tools/faqs/faq.cfm?id=427&t=3). So as of 2014, about 100 times as much electricity was generated by coal as by solar.

Natural gas is in second place, and while much cleaner than coal, it still produces the greenhouse gas CO2, as well as nitric oxides that contribute to photochemical smog. In third place is nuclear, and the problem of nuclear waste is still an unsolved problem. Who buys the nuclear plants after their 50-year lifetime is up?

It is a scam to promote minisplits as running on "clean electricity" without accounting for the fact that 85% of the electricity today is produced by coal, natural gas, and nuclear, all which present their own environmental costs.

Posted By fredjmillard on 23 Dec 2015 09:22 AM
Is that something BEopt can calculate, the heat loss per hr? I showed my better half the mini ductless splits and she does not like the look of them and would rather just have registers. If I were to do hydronic radiant heat in the floor, I would still need a separate system for cooling correct? What is the experience on here with a system like the unico for cooling? Thanks Fred

You do know that they have ceiling mounted minis that look just like any other register? They also make ducted mini-splits. FWIW, we have the plain, ugly wall-mounted units, and you don't 'see' them after a while.

Lee,

I changed the windows in beOPT from u=0.26 SHGC=0.31 to the option that all back windows have HIGH SHGC. My heating load actually went up with everything else being equal. Is there a different way to compare high solar heat gain in BEopt?

Changing around a few other parameters I have my heat load at 50.5kBTU/hr and 20.5kBTU/hr cooling. I used a weather file in BEopt to figure out what the design temps the used. I believe interior was 71F for heat set point and 75F for cooling.

Thanks
Fred

Posted By Lee Dodge on 24 Dec 2015 05:43 PM

Posted By Dana1 on 23 Dec 2015 03:02 PM
The whole coal-fired power grid efficiency blah-blah is a total straw man argument. Coal is toast, dead, DONE- stick a fork in it! The grid-supply mix in 2009 isn't what it is in 2015, and isn't anything like what it will be over the lifecycle of a mini-split. Try this one on for size: A shiny-new combined cycle gas plant delivers about 50% efficiency from source fuel to load after grid losses. A cold climate mini-split running full-blast delivers a COP of about 1.8 at -25C/-13F, and much higher when its above +10F and modulating. Your worst-case fuel efficiency would then be 1.8 x 50% = 90%, and your average fuel-load efficiency would be north of 100%, were the grid supplied completely by combined cycle gas. But it isn't, at least not this week.

Maybe in your fantasy world, coal is dead. But for those of us working in the real world, we look at the graph presented in your reference and it shows that electricity generation by coal in Michigan outstrips second place by more than a factor of two!

In your fantasy world, electricity is a clean energy source, but pull back the curtain and notice that coal dominates electricity production in the U.S., ahead of all other sources. The proportion of electricity generated by coal is dropping, and solar is gaining, but solar is only 0.4% while coal is 39% for the U.S. as a whole (https://www.eia.gov/tools/faqs/faq.cfm?id=427&t=3). So as of 2014, about 100 times as much electricity was generated by coal as by solar.

Natural gas is in second place, and while much cleaner than coal, it still produces the greenhouse gas CO2, as well as nitric oxides that contribute to photochemical smog. In third place is nuclear, and the problem of nuclear waste is still an unsolved problem. Who buys the nuclear plants after their 50-year lifetime is up?

It is a scam to promote minisplits as running on "clean electricity" without accounting for the fact that 85% of the electricity today is produced by coal, natural gas, and nuclear, all which present their own environmental costs.

BS

If there's a fantasy operative here it's the fantacy world where the grid mix is frozen in time and not rapidly evolving, and that federally mandated carbon emissions from the power sector will be overturned in court. (Bjorn Lomborg, anyone? :-) )

According to the EIA source, 50.2% of all of the estmated 8874 Gwh goning onto the grid in MI in 2015 was from thermal coal.

That #2 slot for MI is legacy nuclear which is nearly greenhouse gas free, and accounts for nearly 23.4% of all power shipped onto the MI grid.

#3 is natural gas, at about 19.9% almost all of which is combined-cycle. The average mix of cc gas across a range of technologies produces at about 0.6x the lifecycle greenhouse gas emissions per kwh of an average range of thermal coal, per the IPCC (https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emissions_of_energy_sources )

So that's 70.1% from fossil sources, 23.4% from nuclear, for a combined 93.5% fossil + nuke. The remaining 6.5% is hydro and unspecified other utility-scale renewables.

Not accounted for in the EIA is smaller scale renewables, heat & power cogeneration, or ANY behind the meter PV, which adds up to another several percent.

The net greenhouse gas of that grid mix feed driving a mini-split in MI is slightly higher than heating with condensing gas today, but it won't be after MI complies with it's Clean Power Plan (CPP) mandate. Even without the CPP mandate (which came prior to the tax subsidy extensions) the EPA was estimating there would an 18% drop in total emissions below 2012 levels per kwh by 2020. Under the mandate MI is required to cut emissions by 39% by 2030. But from a total cost point of view that should be pretty easy to hit, now that the tax credits for PV and the production credits for wind have been extended. See:

http://www3.epa.gov/airquality/cpptoolbox/michigan.pdf

The very strong trend lines are for displacement of coal fired generation with other sources. Coal fired generation in MI has dropped 25% in just the past six years. A simple linear extrapolation of coal plant retirement for the next 6 years put coal at 1/3 of the total grid power by 2022. They won't be replaced by new coal plants at any efficiency level, and the coal plants that will be retired first are those with the least favorable heat rates, improving the average carbon emissions from coal. There's a real difference in the carbon output of newer super-critical coal operating at a high capacity factor and legacy sub-critical coal, and as capacity factors drop due to the higher cost of production against zero marginal cost sources (wind, solar) or low-marginal cost sources (cc gas) the sub-critical coal plants emit even more carbon per kwh, and cost more per kwh to keep them running. They're going away.

The cost of current technology wind power is comparable to current technology combined cycle gas, which are competing head-to-head for new generation in most midwestern markets (even without carbon taxes) and the production tax credit extension for wind is long enough to make it EXTREMLY cost-competitive against cc-gas as coal & nuke replacement by the time that subsidy expires.

The only states in the US where 85% or more of the power is from coal are West Virginia (http://www.eia.gov/state/?sid=WV#tabs-4 ) , and Wyoming (http://www.eia.gov/state/?sid=WY#tabs-4 ). According to IEA data, even in China (the world's largest emitter) "only" 66% of the primary energy is coal, and only 77% of the grid power is from fossil sources (all types, but primarily coal), with the majority of the rest being hydro, not nuclear.

Most of the environmental footprint of Michgan's legacy nukes has already been dealt- the marginal environmental impact of keeping them running is miniscule compared to the marginal impacts of combined cycle gas or coal. Heating with a mini-split doesn't add much on that front compared to heating with the marginal impact of heating with condensing gas. The overall marginal cost of keeping nukes running is challenging against the cost of new cc-gas and wind power. With the CPP mandate legacy nukes may be getting a bit of life extension, since replacing them with cc-gas can't happen unless roughly twice as much coal-fired capacity is retired at the same time, or there would be an increase in state emissions, emissions that are mandated by regulation to become lower over time. But it's only a matter of time before they succumb to the accelerating cost reductions happening in wind & solar.

Running a quick spreadsheet calc against the EPA's 2012 estimated grid emissions numbers and the mandated numbers for MI in 2030. (http://www3.epa.gov/airquality/cpptoolbox/michigan.pdf )

In 2012 a mini-split operating at a seasonal average COP of 3 would have been dumping 188 lbs / MMBTU of CO2 into the atmosphere. It's already considerably less than that in 2015.

By 2030 under the CPP mandate it would be ~114 lbs/MMBTU.

Burning natural gas delivers ~117 lbs/source-fuel MMBTU into the atmosphere. ( https://www.eia.gov/tools/faqs/faq.cfm?id=73&t=11 )

At a seasonal average combustion efficiency of 95% that's 123 lbs/MMBTU-delivered , plus the carbon footprint of the power used by the pumps, air handler & controls etc.

So sure, on day-1 there's lower emissions from condensing gas, and a mini-split in 2016 might be as bad or worse than heating with code min 82% gas (when factoring in air handler power on a cheap split capacitor air handler motor). But by 2030 the mini-split be slightly lower than condensing gas if Michigan just barely complies with it's CPP target.

Odds are pretty good that MI will beat that with margin by 2025, given the exponential trend lines on the costs of wind & solar in that time frame.

Fred,

I think that the choice of windows will have little effect on the size of the furnace that BEopt computes. The peak heating load occurs at around 6 am when there is no solar energy entering the house. In fact, with high solar gain windows, the U values (thermal conductivity) will be slightly higher and therefore the peak heating load will be slightly higher.

However, the annual heating energy and costs will often be a little lower with the high solar gain windows since there is energy gain during the daylight hours. BEopt provides both energy usage (heating and cooling) and dollar costs (heating and cooling) in its output. I will try to run some numbers, but no promises.

The furnace size (heating capacity) looks about right to me, but I will try to take a look at it in more detail. I get a annual usage of 518.5 therms/yr of natural gas from BEopt for a similar sized house in Chicago climate with a similar peak heating load, which sounds reasonable depending on how well insulated the basement is from the house. At $0.80/therm, this would be an annual fuel cost of $415, excluding connection fees, which sounds very reasonable to me. Hot water heating, cooking, and any gas appliances would add to that value.

Fred,

In using BEopt, you must choose a value for air infiltration rates, and that has a major effect on heating loads. The default value is sort of high for a new house; I think that it is 7 ACH @ 50 Pa. It might be reasonable to target for 3 ACH @ 50 Pa, especially for that large a house.

What is the R-value for the SIPS. Depending on the rigid foam used, the values can vary.

For a walk-out basement, you might need to use significantly greater than code-minimum basement wall insulation, which it looks like the Xi wall provides (only code minimum) unless you fill in the area between the studs with more insulation.