Laura Diane
New Member
Posts:24
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| 03 Mar 2017 07:29 PM |
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Planning to build 1440 sqft. passive/active solar home on whole-house slab (24x60) with hydronic in-floor heat. trying to decide: propane or electric boiler? Considering electric since I have 35 ea. 75 watt solar panels(35x75=2625W) and a good amount of solar days where I live in northeast Oregon (Enterprise,OR) Winters are long and very cold here at 45 deg. latitude. Planning to utilize as many energy efficient features as I can afford -- triple glazed windows, extra insulation. Would like solar-heated water, if I can afford it, or to plan for adding at later date. In deciding propane or electric, I'm also considering propane for kitchen range, ribbon fireplace and patio firepit/BBQ. Houseplan similar to attached photo |
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ronmar
Basic Member
Posts:479
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| 03 Mar 2017 10:13 PM |
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The problem with solar electric for heat is that it will be at it's best when you need it the least due to passive gains and typically higher daytime temps. Unless you have some way to store the heat for when you need it or you are planning on net metering to offset your non daylight electric usage, I don't see your panels meeting a very large precentage of your heating or electric needs.
My ideal for this would be micro-inverter grid tied solar feeding an air source Heat Pump(and the rest of your house loads during the day). This HP would charge an insulated storage tank and be programmed to only run during the day unless the storage was drastically low. This has the advantage of multiplying your KW usage by the COP of the heat pump. IE: 2KW will give you roughly 7KBTU/Hour thru direct electric heating. Thru a heat pump at a 3.0 COP that same 2KW could give you 21K BTU/Hour, This sort of system would still make the most of your KilloWatt hours even if run at night. But it has the disadvantage of requiring space for heat storage and adding cost and complexity.
One thing you will need to know to help this decision is your energy requirement. So pick a target window U factor and envelope insulation standard. Total the surface areas at the various R values and using your design temps calculate a heat loss. There are programs out there to help you do this yourself or hire it done. A calculated usage along with prices for electricity and propane should help you with this decision and many others involving the way you meet the needs of this house. IMO it is step one and will drive many of the other decisions you make. That is one of the reasons I would initially do these calcs myself or use a piece of software. This way you can make changes to insulation values or window/door areas and see how they effect the energy required at a given outsde air temp.
Northwest electric power rates can be lower than other parts of the country, so it may be a tossup as to which is the most economical but you need the heat loss calcs to determine that. Insulation bought and paid for now however may drastically offset future energy increases...
Good Luck on your project. |
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Laura Diane
New Member
Posts:24
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| 03 Mar 2017 11:50 PM |
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Thanks for your input. Was planning on grid-tied solar. So you're saying your choice would be air source heat pump over hydronic, based on efficiency and overall performance? My builder didn't seem thrilled when I mentioned hydronic, didn't find out why, yet. Any links or reccs on who to hire for the heat loss calcs? Roughly how much space and added costs are you talking about, for the heat pump? |
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jonr
Senior Member
Posts:5341
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| 04 Mar 2017 08:51 AM |
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Take a look at the Chiltrix hydronic air source heat pump. The use of thermal storage depends on your grid-tie financial terms. Ie, if the grid is willing to provide low cost storage, use it. If not, a large tank of water + a hydronic heat pump can use PV solar for space and water heating with minimal use of batteries. |
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ronmar
Basic Member
Posts:479
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| 04 Mar 2017 01:33 PM |
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Posted By Laura Skovlin on 03 Mar 2017 11:50 PM
Thanks for your input. Was planning on grid-tied solar. So you're saying your choice would be air source heat pump over hydronic, based on efficiency and overall performance? My builder didn't seem thrilled when I mentioned hydronic, didn't find out why, yet. Any links or reccs on who to hire for the heat loss calcs? Roughly how much space and added costs are you talking about, for the heat pump?
Not a heat pump air heater, an air source heat pump water heater/boiler like the Chiltrix jon mentioned. Not a clue who to contract with for the heat loss calcs in your area as I do my own. For a DIY Try Borst engineering they have some pretty cool heat loss and hydronic calculators on their website free for personal use. Once you get your brain around the values you are entering(very detailed instructions), the are quite easy to manipulate and tweek to see how changes effect the heat loss/energy used. The space requirements i was refering to are only if you are trying to store heat(VERY large insulated water tank). Something like a chilltrix actually goes outside, it is basically the outside portion of a mini-split heat pump with a gas to water heat exchanger and water pump in place of the inside unit. That and either an electric or propane boiler as a backup/augment might be a good mix for you but you need the heat loss numbers to help choose which path. Your GC's reluctance on radiant may be because he has no experience(or a bad one) with it... |
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Dana1
Senior Member
Posts:6991
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| 06 Mar 2017 04:18 PM |
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What are your electric power rates? Do you have the option of time of use rates?
The upfront cost of an electric boiler is dirt-cheap and extremely low maintenance in comparison to propane, and your 99% design heat load is probably going to come in under 20,000 BTU/hr @ +10F (your approximate 99% outside design temp). A reversible chiller is even more expensive up front than a propane boiler, and there is the question of local support. Electric boilers are cheap, dumb as a box o' rocks, and quite rugged.
In your location an electric boiler operating off a floor thermostat to keep the floors toasty, and a 1-ton cold-climate mini-split for setting the air temperature would be a reasonable compromise, and would offer high efficiency air conditioning as well. You could size the mini-split to carry the full heat load if need be, which would use 1/3 the power of the electric boiler, but sizing the electric boiler for the full load is pretty cheap insurance, even if you're only using it for keeping the slab at a comfortable temperature.
But don't spec the mechanicals until/unless you've run the real heating & cooling load numbers. |
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loghomebuilder
Basic Member
Posts:119
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| 07 Mar 2017 06:06 PM |
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I don't mean to steal this thread however, I was told my heat loss calculations are 54,600 Btuh heat loss @ -9 degrees OAT.
I can't seem to find an air-to-water system that would supply these BTUs. Do they simply not exist???
I will say that while we do get into the single digits, we don't usually get below zero plus, so that part seams to me to be a bit extreme.
I will also have a wood stove and could fire that up on the coldest nights without issue. |
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toddm
Veteran Member
Posts:1151
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| 07 Mar 2017 08:29 PM |
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A smallish storage tank could greatly increase the efficiency and output of an air-to-water heat pump. The pump would be working at daily highs in COP as it charged the tank through the day. A modern (that is European) indoor wood stove boiler can handle the rest through the evening. http://www.hydro-to-heat-convertor.com/pricing.html I burn an British wood stove boiler 8 to 12 hours a day in deep winter to heat a 1600 sf house. The stove heats a 200 gallon tank which in turn heats radiant floors on thermostats. I use three to four cords of wood a season. |
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ronmar
Basic Member
Posts:479
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| 07 Mar 2017 08:53 PM |
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Posted By toddm on 07 Mar 2017 08:29 PM
A smallish storage tank could greatly increase the efficiency and output of an air-to-water heat pump. The pump would be working at daily highs in COP as it charged the tank through the day.
And when your grid-tied solar is providing most of the power it uses:).
Loghomebulder, 54Kbtu IS a lot. I know they make air source pool heaters that large, but not sure what their low temp outputs and efficiencies would be... |
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sailawayrb
Veteran Member
Posts:2275
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| 08 Mar 2017 11:50 AM |
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Laura, for heating I would suggest considering hydronic radiant floor heating and using a NextGen electric boiler. For cooling I would suggest a whole house attic fan. Unless you get your passive solar design badly wrong, you shouldn't need AC.
My 2400 sf single story home in southern OR is also passive solar (4' roof overhangs), hydronic radiant floor heating (using the smallest 4 kW or 13,652 Btu/h NextGen electric boiler which is almost twice my 19F design heat load), HRV, whole house attic fan (which eliminates any need for AC), constructed with BuildBlock ICF, uses much interior thermal mass (e.g., 5" thick stamped concrete floors, 22" thick castle-like brick/rock faced masonry interior wall, masonry heater (using Nobert Senf Heatkit core) and granite kitchen counters and has R60 ceiling insulation (combination of polyiso under the attic floor and blown fiberglass elsewhere). Many Summer day highs are generally over 90F and several are over 100F and can even reach 110F on occasion. Our Summer day lows are typically 40-50F lower than our highs. The house indoor temperature has never exceeded 70F. I also much prefer cool fresh evening air over AC air. Of course, this cooling strategy only works in low humidity diurnal climates, but this is how we design/build homes here.
Gayle |
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| Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do! |
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jonr
Senior Member
Posts:5341
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| 08 Mar 2017 12:24 PM |
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Consider a heat pump (hydronic or air) to provide most of your load plus an electric boiler to supplement it only when/if the HP can't keep up. |
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BadgerBoilerMN
Veteran Member
Posts:2010
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| 09 Mar 2017 11:29 AM |
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Dana is always right.
I have an Electric and a propane boiler, plus a dual-head (two zone) HyperHeat Fujitsu in my slab-on-ground office/shop.
First a proper heat load, then fuel cost comparison with consideration of the floor plan, especially for the air conditioning aspects including, filtration, ventilation and humidification.
Solar is a long-term investment with a short return. More especially when space heating in cold climates.
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| MA<br>www.badgerboilerservice.com |
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Dana1
Senior Member
Posts:6991
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| 09 Mar 2017 02:27 PM |
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Posted By BadgerBoilerMN on 09 Mar 2017 11:29 AM
Dana is always right.
I dunno 'bout that- maybe you should take that up with my wife! ;-)
Whenever we disagree one of us ends up apologizing, and the other always says "I know you mean well, Dana, and I'm sure you'll do better next time." |
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Laura Diane
New Member
Posts:24
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| 09 Mar 2017 03:05 PM |
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Power rate avg. is 11 cents/kwhour in Oregon
Time-of-Use rates? - Yes, we have that option
Grid storage - not sure how to answer. Power produced in one month can only be carried forward to future months, up until March billing, when the yearly cycle "starts over".
re: mini-split -- confused why I would need this? I don't need any A/C, and there will be no ductwork (just in-floor pex)
So, in addition to an electric boiler (which I'm now strongly leaning towards) what other components do I need? (do I NEED a mini-split?) or are you just recommending the mini-split as a cheaper backup option than using the electric boiler on cloudy days/no solar?
Does the electric boiler provide domestic hot water also?
What do you recc for that, in my scenario? As mentioned earlier, I may go with evac. solar tubes at a future date -- would this affect my choices now?
Sorry for my naivete here |
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Laura Diane
New Member
Posts:24
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| 09 Mar 2017 03:21 PM |
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Posted By Dana1 on 06 Mar 2017 04:18 PM
What are your electric power rates? 11 cents/kwh Do you have the option of time of use rates? YES WE DO
The upfront cost of an electric boiler is dirt-cheap and extremely low maintenance in comparison to propane, and your 99% design heat load is probably going to come in under 20,000 BTU/hr @ +10F (your approximate 99% outside design temp). A reversible chiller is even more expensive up front than a propane boiler, and there is the question of local support. Electric boilers are cheap, dumb as a box o' rocks, and quite rugged.
In your location an electric boiler operating off a floor thermostat to keep the floors toasty, and a 1-ton cold-climate mini-split for setting the air temperature would be a reasonable compromise, and would offer high efficiency air conditioning as well. DON'T PLAN ON NEEDING A/C AT ALL You could size the mini-split to carry the full heat load if need be, which would use 1/3 the power of the electric boiler, but sizing the electric boiler for the full load is pretty cheap insurance, even if you're only using it for keeping the slab at a comfortable temperature.
But don't spec the mechanicals until/unless you've run the real heating & cooling load numbers.
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Laura Diane
New Member
Posts:24
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| 09 Mar 2017 04:23 PM |
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Thanks for the reply. I also contacted you via your website, not sure if you got that, then read that you are booked up for '17, so figured I might not hear back.
Don't plan to have A/C, never have needed it in the past. With a 2/12 pitch shed roof, what should my overhangs be? Might have overglazed south wall (haven't done the calcs yet) but could easily take out south facing windows from the plan. Do love the "window wall" look and our view is stunning, but concerned about summer/fall overheating. Don't plan on having HRV. Where did you purchase your NextGen boiler? Or should I just tell my electrical contractor that is the brand I want? Would you recc. an air source heat pump, as others on here have, in addition to the NextGen? What about Domestic Hot Water heating? And the fact I'd like to add solar hot water at a later date....would that affect my choices now? |
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Laura Diane
New Member
Posts:24
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| 09 Mar 2017 04:26 PM |
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Thanks for the reply, Gayle. I also contacted you via your website, not sure if you got that, then read that you are booked up for '17, so figured I might not hear back. Don't plan to have A/C, never have needed it in the past. With a 2/12 pitch shed roof, what should my overhangs be? Might have overglazed south wall (haven't done the calcs yet) but could easily take out south facing windows from the plan. Do love the "window wall" look and our view is stunning, but concerned about summer/fall overheating. Don't plan on having HRV. Where did you purchase your NextGen boiler? Or should I just tell my electrical contractor that is the brand I want? Would you recc. an air source heat pump, as others on here have, in addition to the NextGen? What about Domestic Hot Water heating? And the fact I'd like to add solar hot water at a later date....would that affect my choices now? |
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Laura Diane
New Member
Posts:24
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| 09 Mar 2017 04:28 PM |
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Thanks for the reply, Gayle. I also contacted you via your website, not sure if you got that, then read that you are booked up for '17, so figured I might not hear back. Don't plan to have A/C, never have needed it in the past. With a 2/12 pitch shed roof, what should my overhangs be? Might have overglazed south wall (haven't done the calcs yet) but could easily take out south facing windows from the plan. Do love the "window wall" look and our view is stunning, but concerned about summer/fall overheating. Don't plan on having HRV. Where did you purchase your NextGen boiler? Or should I just tell my electrical contractor that is the brand I want? Would you recc. an air source heat pump, as others on here have, in addition to the NextGen? What about Domestic Hot Water heating? And the fact I'd like to add solar hot water at a later date....would that affect my choices now?
Posted By sailawayrb on 08 Mar 2017 11:50 AM
Laura, for heating I would suggest considering hydronic radiant floor heating and using a NextGen electric boiler. For cooling I would suggest a whole house attic fan. Unless you get your passive solar design badly wrong, you shouldn't need AC.
My 2000 sf single story home in southern OR is also passive solar (4' roof overhangs), hydronic radiant floor heating (8 kW NextGen electric boiler), HRV and whole house attic fan (no AC), constructed with ICF, and has R60 ceiling insulation (combination of polyiso under the attic floor and blown fiberglass elsewhere). Many Summer days are over 90F and several are over 100F. The house indoor temperature has never exceeded 75F. I also much prefer cool fresh evening air over AC air. Of course, this cooling strategy only works in low humidity diurnal climates.
Gayle
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Laura Diane
New Member
Posts:24
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| 09 Mar 2017 04:34 PM |
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Sorry for the multiple posts everyone..... obviously, I don't know how to reply to individual posts, or how to delete my duplicate posts. |
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Dana1
Senior Member
Posts:6991
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| 09 Mar 2017 05:16 PM |
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I don't have a website, so I assume that wasn't for me.
Solar hot water doesn't make economic sense anymore, now that there are heat pump water heaters and $3/watt photovoltaic (PV) power. A decade ago that wasn't the case. Spend the solar hot water money on more PV even if you skip the heat pump water heater and go with a cheap electric tank. PV is much lower maintenance, and has a much better financial rationale. Rooftop real-estate is limited, so use it for the premium output product (electricity), rather than low-grade thermal.
HRV ventilation is "worth it", even if it's just a single $1000-1600 non-ducted Lunos E2 or Nexxt At IRC 2015 code-maximum air leakage of 3ACH/50 many houses will not get sufficient "natural ventilation" (aka "infiltration"), and even if the volume of natural ventilation is enough for the house, there is no guarantee that it's going to the places that need it the most, or that the path where it comes in is acceptably clean. Building the house as tight as possible and installing ventilation in the appropriate places & volumes is really the right thing to do. Exhaust-only ventilation can work if you provide inlet vents in the appropriate places, but it adds to the heating load and injects an uncomfortably cool drafts at the inlet point(s).
Over-glazing induces overheating even in winter, and increases the peak heating load (even though it reduces heating energy use.) Spending some of the high-performance glass money on more insulation or rooftop PV is often a better investment in both comfort and energy cost savings. In your climate the heat from an appropriately sized decent quality ductless mini-split costs less than 1/3 of getting the same amount of heat from an electric boiler, so going sparingly on the radiant slab temperatures with the electric boiler and bumping up the air temperature with the mini-split will in most cases pay for the mini-split in less than 5 years, even if you never use it for air conditioning.
Over glazing the west wall can induce truly torrid peak air conditioning loads even in temperate climates, and west windows aren't readily shaded by overhangs. |
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