I'm in the early stages of designing a new house. I have many questions, but I think starting with two and depending on the answer(s) ask follow-up questions. Question #1 What is the most efficient form of heating? a] Radiant floor heating? b] Radiator on the wall? c] Forced air? d] Other My guess is floor heating because cold feet result in turning up the heat. I think it also has the most equal distribution of heat. Question #2 What is the most maintenance free and durable? I would greatly value expert input.

#1: Air Source Heat Pumps (aka minisplits)
#2: These are relatively new, although heat pumps have been around for decades, but they seem to be pretty trouble free. Follow Building Science Corp guidelines for an easy to heat, long lasting home.

THanks for the quick reply Bob!


Is that also true compared to natural gas?
Building in climate zone 4: http://energyiq.lbl.gov/EnergyIQ/images/climzonenew.gif
I don't know if it even can be compared.... for geothemal I read about COP 4-5. What's the COP of a minisplit?|

I've read the specs on the Mitsubishi site; while not claiming I understand it all, performance varies with outdoor temp (assuming constant indoor temp)

The COP of GSHP may be higher than ASHP since they are using warmer source. The initial cost of GSHP , however, is quite a bit higher. The COP was 2.5-3, but may have changed with the new models.

Natural gas costs about $1.05/therm = $0.036/kWh @80% efficiency that's 0.045 kWh
Electricity costs about $0.12/kWh. Adjusting for COP=3 that's $0.06 kWh.
Doesn't that mean gas heating is 33% cheaper?

You're building a new house, so I'm assuming you are thinking long term. Gas will (not "may") increase. If you install photovoltaic panels, the fuel price will remain constant at -0-, and your panels will be paid off years before the panels need replacement. We are building a 2200 sf house which will have an 8.7 kW system which should cover all of their electrical needs including heat & HW, & will cost the (net after rebates) under 18k.

Some tests:
http://www.nrel.gov/docs/fy11osti/52175.pdf
http://www.nrel.gov/docs/fy12osti/54846.pdf
The way I read it, COP is worst when it's needed most.

I've considered a PV system but it looks very costly to me. Especially the battery bank is very expensive. So I wonder how long it takes for a complete system to pay itself back.

Posted By NewHoosier on 04 Aug 2014 11:21 AM
Natural gas costs about $1.05/therm = $0.036/kWh @80% efficiency that's 0.045 kWh
Electricity costs about $0.12/kWh. Adjusting for COP=3 that's $0.06 kWh.
Doesn't that mean gas heating is 33% cheaper?

Math problem: $0.12/3.0= $0.04/kwh , and not $0.06/kwh

And in US climate zone 4 you would get a seasonally averaged COP of about 3.5 or better out of a better-class mini-split. In-situ field monitoring by the NEEA showed that a cluster of 12 older-model Mitsubishi -FE12s averaged a COP of about 3.0 in Idaho Falls ID, which is climate zone 6. As part of the same program the even larger averages over a wider range of models in Seattle (marine zone 4, with more losses to defrost cycles than Zones 4A & 4B) averaged 3.5 ish.)

$0.12/3.5= $0.034/kwh


The newer MSZ-FHxxNA series units are about 15-20% more efficient than the -FExx series. In a zone 4A climate you could be averaging a COP of 3.8-4.0 with one of those, which would put you at about 3 cents/kwh of heat, which is 33% cheaper than heating with 80% efficiency gas (assuming no system losses OR electricity use with the gas-fired system, which is never the case.)

"The way I read it, COP is worst when it's needed most. "

That's true of all air source heat pumps, but so what? Do you get billed as a function of your peak draw?  Size it such that it has sufficient  rated capacity at your 99% outside design temp, and let the thing modulate at part load 99% of the time, where the COP efficiency is much higher. The -FH12NA has a COP of 3.5 even at +17F at part load, and at -13F still pulls a COP of 2.0 at full speed. (It also has a turn down ratio of more than 5:1, which is better than prior generations- it'll modulate MOST of the time.) In the shoulder seasons it'll be running a COP of 4 or better.

BTW: Bob- these things are NOT relatively new (unless you're talking "relative" to hydronic boilers or something.)  Mini-splits were introduced in Japan in 1968 when Mitsubishi released the "Kirigame" mini-split air conditioner, a nearly instant success since window-shaker air conditioners were maladapted to Japanese architecture.  (That's more than 45 years ago!) Multilple vendors got into the game all over Asia prior to 1980.  Multiple speed heat pump versions have been around for more than 20 years now, and fully variable speed versions with scroll compressors and variable refrigerant showed up prior to the turn of the millenium. They're only "relatively new" to colder parts of the US where previously heat pumps weren't that viable, but even cold-climate mini-splits have a decade or more of US-installed cold climate experience behind them.  These are well evolved designs that developed in a cost & reliabity competitive environment, not some latest-craze gizmo idea soon to be scrapped.

Math problem: $0.12/3.0= $0.04/kwh , and not $0.06/kwh

Maybe I misunderstand COP....?
The way I understand the rating:
- COP=3
- The mini-split uses 1 unit of electricity. Say 1kWh.
- It adds heat to the room equivalent to 3 untis. That's 3kWh in my example.
- The 1 kWh used by the mini-split is not heating my house so it's wasted.
- So the net result is 3kWh(in my house)-1kWh(outdoors)=2kWh(saved on electricity)
????

"The way I read it, COP is worst when it's needed most. "

That's true of all air source heat pumps, but so what?

A lower COP is a longer earn back period because my electricity bill goes up. I also need a bigger (= more expensive) unit for really cold weather and if to cold it completly stops working? Maybe I need backup heating equipment which also adds to the cost?

The -FH12NA has a COP of 3.5 even at +17F at part load, and at -13F still pulls a COP of 2.0 at full speed.

So, at -17F natural gas is more cost efficient?

Please don't view my questions as doubting my your knowledge but as increasing mine :-)

Granted the original question was about efficiency, but because you said you are in the design stage there is something else to keep in mind about heating, and that is perceived comfort. Air source heat pumps, whether in a central forced air system or in a mini-split, have a much different feel than radiant heat. Not such a big deal in my mild climate where my ASHP is just fine. But in Indiana I suspect you have longer colder periods. A breeze of 68 degree air is not going to warm your bones.

Jelly, all input is welcome. I have MANY questions but decided to ask one at the time instead of dozens.
Comfort was/is on my list. Unfortunately, that's a trade off too. Floor heating is the most comfortable in theory. No carpets. That's the first tradeoff. But carpets aren't allowed for passive (sun) heating anyway (with the exception of a trombe wall)

The effect of floor heating lessens as the home gets more energy efficient. A very leaky home requires lots of heating. So the floor heating is running overtime. Comfy on the body but not on the wallet. Now consider a 100% efficient house. Heat spreads equally. The floor heating is off all day. Real life situations are somewhere in between. My point is that e comfort of floor heating only is present when heat is added. At that should be as little as possible. With a well insulated house the heat from a ASHP is distributed equally. In general I don't like 'mechanical draft'. Somehow it's always different from natural draft. Houses, offices, cars, air planes all have AC. None of them match a nice cool summer breeze.

But I'm old enough to know it's (next to) impossible to find ideal in this world.

BTW check out page 32 of this document. A breeze of up to 132 F.
http://www.nrel.gov/docs/fy11osti/52175.pdf

Posted By Jelly on 04 Aug 2014 04:08 PM
Granted the original question was about efficiency, but because you said you are in the design stage there is something else to keep in mind about heating, and that is perceived comfort. Air source heat pumps, whether in a central forced air system or in a mini-split, have a much different feel than radiant heat. Not such a big deal in my mild climate where my ASHP is just fine. But in Indiana I suspect you have longer colder periods. A breeze of 68 degree air is not going to warm your bones.

The exit air temp of mini-splits are north of 100F when it has 65F air coming in.  It's definitely closer to the warm summer-breeze, until it's SO tapped out on capacity with super low outdoor temps that the delta-T at the interior coil begins to drop.  For cold climate mini-splits chilling exit temps only  happen at outdoor temps well below zero at the maximum blower speeds, when it's fully tapped out on heating capacity.

Even ground source heat pumps & ducted ASHP systems typically deliver exit air north of 85F, and while it can be pretty tepid when sitting in the breeze, but nothing like the wind-chill you'd get with sub-75F air at the registers.

A COP of 3 doesn't mean the 1 kw of power used was wasted must be subtracted. It means that at 1kw of continuous input 3kw of continuous heat is being delivered inside the house. Some of that not-so-wasted 1k is heat in the blower motor, which is fully indoors, and some of it is compressor motor heat that made it into the refrigerant.

But COP is never measured at that micro-level, and it doesn't really matter where that 1kw ultimately ends up- the COP efficiency of the unit is always measured by the amount of heat actually DELIVERED for the amount of electricity used.

The binned hourly outdoor air temperatures in January at Hoosierville locations is about 25F, and warmer the rest of the heating season. Insert your zip code here, zoom in/out to cover the month of January and eyeball it using the cursors:

http://weatherspark.com/#!dashboard;a=USA/IN/Crawfordsville

The 99% outside design temps are all in positive digits F territory:

http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf

That means that you are only suffering that 2-ish COP for 1% of the time, and does not dramatically affect the seasonal average. The efficiency & load at the average winter temp is closer to what your full seasonal average will be. At ~+25F outdoor temps at 2/3 load you'll be hitting north of 3.0 with a -12RLS2-H, and north of 3.5 with an -FH12NA

Sure, at sub-zero temps, maybe even at +10F, at your utility rates 80% efficiency gas may be more cost effective than a mini-split but that's less than 10% of the time.

Most mini-splits never stop working, even at very cold temperatures. I've corresponded with folks in Quebec who heat with mini-splits who swear it's still putting out pretty good heat even at -30F, and MANY people in Vermont & Maine still use them in temps below -20F. It would be very unusual indeed to need a full back-up for the 99.9th percentile temperature bin- the mini-split will still be delivering the lions share of the load, if sized for the 99% outside design temp.

A 1500 Watt plug-in space heater costs maybe $50 up front for a nice oil-filled radiator version, and will deliver 5000 BTU/hr into a room. In a high-performance house that's more than 25% of the total heat load. (In my 2400' not-so-high-R 2x4 framed antique it's about 15-17% of the load at my 99th percentile temperature bin of +5F.) How much resistance auxiliary heating you use depends on how well you sized it, but it doesn't have to be a significant capital expense.

Some of that not-so-wasted 1k is heat in the blower motor, which is fully indoors, and some of it is compressor motor heat that made it into the refrigerant.

That's entirely correct, but also consider that the same not-so-wasted heat works against you when cooling the house. I'm in no way able to give you scientifically backed numbers but I think winter gain and summer losses my come close to zero when added. All mechanical engery is 'lost'.

An example of what I mean.

700Wh heat gained during the winter. That's COP1 heat
700Wh heat needs to be removed during the summer. At COP3 that costs me 700/3=233Wh
Net heat gain = 467Wh
During the winter 300Wh 'mechanical energy' is lost.
During the summer 300/3=100Wh 'mechanical energy' is lost.
467+300+100=867Wh
Add to that the fact is wears out the pump. The removing of the heat generates a bit of heat. That's getting pretty close to 1kWh.

BTW all the above doesn't mean I don't value the info in your message. On the contrary. It's just that for me to believe things it helps a lot if I understand them

I don't need al the details but how can Maual J be calculted by a professional?
When I build a new house nothing is know. I have no utility bills to show.
How do they take thinks like passive heating into account? How they know if I don't open windows when cooking or my dog constantly opens my door (just examples)
I think those are important questions for sizing the mini-split.

Is it possible to put a mini-split on the roof? I'm planning the utility room as the center of my house. The advange of that is lots less ductwork for conventional HVAC.. Basically all I need is 4 holes in the wall of my utility room to heat 4 parts of my house.
I know, if I understand thinks correctly, a mini-split has no ductwork but I just want to be as future proof as possible. Maybe mini-split is disappointing and I put in a gas furnace or geothermal.

As you surely have noticed from my spelling I'm not from the USA. I live in the Netherlands (and want to move to IN). Here the vast majority of homes are natural gas heated. So my mind is very conditioned in thinking about that sort of heating. Anyway some old houses have little fixednatural gas heaters the size of the 1500W space heater you mentioned. Could be an option as backup heater. Dunno if it cost me to get gas connected. (here it's free) I cook on gas.

How do they take thinks like passive heating into account?

It's a function of the home's siting, exposure, orientation, local weather, window size, location and construction among other things. Sometimes, it's just estimated.

How they know if I don't open windows when cooking or my dog constantly opens my door (just examples)

Some lifestyle factors need to be estimated. You might get a higher estimate for your air changes per hour.

I don't need al the details but how can Maual J be calculted by a professional?

It can be calculated from a houseplan which includes construction details.

Is it possible to put a mini-split on the roof?

It seems like a good place to put it in Indiana would be mounted on the wall, high up under the eaves where it is out of the sun, snow and rain.

The advantage of that is lots less ductwork for conventional HVAC

Don't forget to provide for ventilation if you use the minisplits. A ventilation system is much less involved than conventional HVAC forced air system.

Your attempting to parse the COP a bit finer than it is actually measured and specified. Yes, the summertime net-COP is reduced by the amount of heat dissipated by the sub-systems ( but not all of that heat is dissipated inside, most of it is dissipated in the outdoor unit). But the basic COP measurement is the same- it's the NET cooling, not the cooling minus the heat dissipated by the indoor unit that is measured & reported for mini-splits. Since there is no way to sub-measure that heat- it's the full-system net COP. With ground source heat pumps the manufacturers specify the COP of the heat pump unit itself, but the net system COP that covers all pumping & air handler power does not appear, since those system design details are not within the control of the manufacturer, and left up to the system designer. With mini-splits all power is delivered in one place- it's a "system in a can", and only the net-COP can be directly measured, not some sub-system COP. (The same is true for window air conditioners and point terminal heat pumps & air conditioners.) Subtracting off for the energy going into the unit would be double-dipping, producing a lower than reality efficiency number.

The cooling season average COP will be much higher than the heating season COP in Indiana's climate.

There are multiple heat load calculation software packages using Manual-J methods that are commonly used by professionals. Like any other calculation, the input data has to be reasonably accurate ( the garbage-in <==> garbage-out problem), but those packages are pretty easy to use. There are inputs to cover heating/cooling loads issues related to cooking, number of hot sweaty humans, (but not dogs :-) ), electrical plug loads, etc.. Heating loads for bedrooms are reduced by ~260 BTU/hour per human, which is of course only an estimate, as are the U-factors of the walls based on the construction materials, and the estimates of infiltration/ventilation rates can differ pretty widely from reality. The methods have inherent error, and the calculated loads are typically 15-25% higher than the eventual measured energy use would indicate.

It's possible to put a mini-split on the roof, but it's more protected from severe hail storms, ice storms, and snow if mounted on brackets under the overhang off the roof. Ice storms are fairly common event in IN, where rain falls from a warmer layer of atmosphere into sub-freezing air near the ground, coating everything in ice, sometimes an inch or more. That amount of ice is beyond what the normal defrost cycling of mini-splits is designed to handle. One solution is to put the mini-split into air-conditioning mode to heat up the coil on the outdoor unit to melt the ice, but it's better to just mount the thing out of direct exposure to rain & snow (and above the historical deepest local snow depth.)

Je bent nederlands he'?! Te gek! Eigenlijk, ik heb nog nooit gemerkd spel fouten of grammatische fouten in je posten. Woonde ik ook in nederland geweest. Dat was boven twintig jaren geleden (en slechts een tien maand verblijf) maar herinner ik nog een woord of tien. Lees ik nederlandse kranten online af en toe- sindts binnenkort iets over de vliegramp in Oekraïne. (Het erg spijt me.)

In most of the US there is a fee for installing a new gas line & meter, and often it is based on the length of new pipe between the gas main in the street to the meter at the house. The details vary- you would have to contact the local gas utility to know what charges (if any) there would be.

Cost is one thing, carbon footprint is another. Indiana's power grid is heavily coal fired, and even at an average COP of 3 it's not clear that the carbon emissions per MMBTU is going to be better than 80% efficiency natural gas. http://www.eia.gov/environment/emissions/state/analysis/images/figure_1-lg.jpg But the grid will get cleaner over time, and the methane emissions from natural gas extraction aren't (yet) nearly as well controlled as they arguably could- be (or the methane emissions from coal mining, for that matter.) It's sort of a coin-toss whether it's greener to go with heat pumps vs. natural gas heating in Indiana, since it requires guessing what policy decisions will be implemented over the 20-25 year lifecycle of the heating equipment. But the potential for much greater use of wind seems viable in IN:

http://ijec.org/2013/07/24/tilting-at-windmills-a-closer-look-at-indianas-expanding-wind-power-industry/

The detractors criticizing wind power in IN can take a lesson for how it works out in other midwestern states, once the learning curve on how to best utilize the wind is understood. Xcel Energy has been able to use big-data crunches to predict more precisely the fluctuating output, as well as how to make use of the ability of rapidly ramping the output of wind farms to stabilize the grid, REDUCING (rather than increasing) the amount of spinning reserves that would otherwise be required, contrary to what many detractors believe. (They are also finding that it's cheaper to include a large fraction of wind power to their grids and reducing the amount of new combined cycle gas in the generating mix.) Whether the policy makers in IN can make this happen or not has a lot of politics behind it- it's tough to guess which way they will go.

But unlike NL, there is a serious need for air-conditioning in IN to be comfortable in the summer, for both removing moisture from the air and lowering the indoor temperatures. Summertime outdoor air dew points are much higher in IN than NL, and the air temperatures are too. A gas heater won't help you much with the air conditioning, but a mini-split can.

With the utility room in the middle and with very short duct runs it's possible to use "mini-duct cassettes" with a mini-split compressor, and the output levels can be more appropriate for high-efficiency houses. A properly sized mini-duct cassette system can still average a heating season COP of 3 or slightly in Indiana's climate, if sized appropriately. The Mitsubishi M-series SEZ-KDxxNA dedicated mini-duct units can work pretty well for modest loads in that sort of configuration. I recently ran through some of the numbers on this series for a guy in Chicago on this thread on another forum:

http://www.greenbuildingadvisor.com/community/forum/mechanicals/36925/minisplit-designmanual-j-question

What's green or not is indeed a difficult discussion so I first aim for a green wallet :-)

Wind and solar energy don't save as much as is often assumed. At least here it isn't. We never have blackout because the there are a adequate (few spare) amount of power plants. What I mean can best be explained with an very extreme example. Assume the whole USA's grid is powered by windmills. But every powerplant needs to stand on stand by in case there is no or not enough wind. So wind power doesn't reduce the number of powerplants. A powerplant can't just switched on like a lightbulb so has to be on stand-by which still uses vast amount of energy. (40% of max?) A similar story for solar energy. The only small exception are tied-to-grid systems which deliver some juice to the grid.


It's not only hot in Indie, but also the winters... My flight back home was cancelled due to extreme cold. That was early January this year. I guess COP will be extremely bad then?


I guess I don't even need an utility room with a mini-split unit on the roof. Then I can just drill a few holes in the roof at the needed locations. But as said I want to be future proof. Just in case I somehow decide to go for gas or geothermal. For that reason I may even install ductwork when building my house. Is there a type of ductwork that is good for all systems currently on the market? If so, what's the size of the ductwork? What would be the best place for ductwork. Celing or floor? I could try to work all the ductwork into my design plan.




One final weird thougt
During ther winter it extracts heat from outside so I was thinking about a mini green house. A glass box with sufficient airflow. Maybe a reflecor to capture extra sunlight. I don't know if that makes sense because I have no if there is air outlit pipe on a unit. Or just a big reflector shining on the unit.