Heating, Cooling, Hot Water: What are my options?

Heating a home which has such a small heat load can be a little more complicated then you think.  Ultimately I think it depends on many factors including questions of the energy source, sustainability,  purpose, etc. You may think "use a heat pump and have it over with!".  But what about other options? Can it be done more efficiently?  Can you plan for less dependency on the grid?  Can you minimize energy to the point where solar voltaic panels become your route to net zero energy?

The nice thing about a Passive House is that you can't build a passive house unless its modelled.  Passive House is a performance standard not a prescriptive one.  A prescriptive standard, like the National Building Code of Canada, tells you how to build a structure to maintain safety, longevity and the health of the inhabitants but it doesn't tell you anything about the performance of the building.  It tells you about the performance of the whole package, upfront, before the building is erected.  As long as you can meet the performance measurements i.e. blower door test, insulation performance, your building will, for the most part, behave the same as the model.

In the previous post I presented the required heating loads for the home.  They are pretty small.  The total load according to wrightsoft is about 2.4 kW.  My designer has used the PHPP software to map out several options for heat/cooling sources.  The modelling has provided me with a way to compare site energy usage for different heat/cooling sources.   See the table below:



The base passive house case uses electricity for everything, but no cooling.  Basically electric resistance heaters for heat, a electric resistance water heater and appliances as energy star with some allowances for energy usage.  Total usage would be somewhere around 12365 kWh per year.  about 3100 kWh is for heating, about 4000 kWh is for hot water and the rest is for appliances.  Keep in mind actual appliance usage will probably be less given that he hasn't derated the power usage based on our appliance choices.

Adding a DMS (ductless mini split) decreases energy usage by about 2155 kWh/year.  Keep in mind that the heating demand was only 3100 kWh but the DMS modelled here also includes cooling.  Total energy usage would be 10210 kWh/year.

Using a HPWH wouldn't actual do anything.  Since a tank HPWH starves the building space of heat, the DMS will work more in the winter to provide heat scavenged from the space.  However, in the summer, the HPWH would cool the space effectively since it extracts heat from he space and sinks it into a hot water tank.  No energy savings but it is an efficient setup.

How about a wood stove in a passive house.  You just need to add a air intake and make sure that the stove has closed combustion....But..woodstoves typically get really hot and finding one with less than 4 kW output is pretty impossible.  That being said, using a wood stove is about as effective as adding a DMS to the house in terms of total energy savings and total yearly demand.  In this case the demand is about 10350 kWh.

How about if you have a system that can use multiple sources?  What if you had a way to heat water, to provide space heat in the winter, and a heat pump water heater to heat the water in the summer?  Now you could have an interestingly efficient system which would allow you to be less dependent on the grid.  Using a wood stove for ambient heat, to create hot water, along with low temperature hydronic radiators the energy usage drops by almost 4355 kWh/year to a total of 8010 kWh.  Now if you add a heat pump to the mix (inside the thermal envelope) the energy usage decreases to 7289 kWh/year!  At $0.0972/kWh, the total yearly electrical bill including heat, lights hot water will be about $708.  The heat pump would be the add on type (http://water.nyle.com/r-series/) and it sits in the mechanical room and can be ducted to the south rooms of the house.  It would draw in warm air from the dining room and expel cool air to the living room since it has the most glazing.

Our hybrid system will be the first of its kind used on one of Passive Design Solutions passive houses,  so it is a bit experimental but we trust the software.  The components will be

1.  WallTherm gasification wood stove (http://www.walltherm.ca).  It will provide air heat, hot water radiation through low temperature rads (30% more efficient than standard rads), and all of our hot water during the heating seasons. Its a beautiful stove and with it's secondary burn chamber its quite a site to watch on a cold evening.

2. The heat pump (http://water.nyle.com/r-series/) will provide us with our hot water in the summer.  It will feed heat through a solar coil exchanger built into the boiler.  The boiler naturally stratifies the water so the hot water stays at the top of the tank.

3. A couple of electric elements will be added to the boiler tank for those times in the shoulder season when you don't want to cool or heat the space.

So there it is.  Basically our hot water and heat will be taken care of in the heating seasons using about 0.5 to 0.75 cords of wood.  In addition, I won't have to run the stove daily if I don't want to. I can store water at 80 C!  So i can burn on a cold day and store enough heat for hot water to get through a couple of sunny days!  Or if it's cold outside, the water in the tank can be used for heating the space.  If we are on vacation, the electric elements in the tank will keep the tank warm.  as long as the water in the tank is above 55 C, the electric elements will never turn on.  In the summer, the heat pump will cool the space inside the house while providing hot water by dumping space heat into the hot water boiler.  Our space cooling requirement appear to almost match our hot water heating requirements so the space should be nice and cool in the summer....Hopefully!

It looks like a beautiful solution and we are going to implement it....I may still add the necessary wiring for a ductless mini split....Just in case!

Comments

  1. We are on much the same wavelength, but some concerns. Just had a quick read of your posting, , so I will comment later.
    Just one for now.....you trust your software. So did Nfld Hydro with Nostradamus for predicting peak load......until DarkNL,,,,,,and they blamed in part Nostradamus. But they neglected somethings you are aware of, like extreme windy cold weather. So now they have a P50 and a P90 forecast, because of the Liberty recommendation. Hydro should have known better! Meanwhile, Nfld is hard to predict with such unusual weather.......you will test and find out how good your software is.
    Do you intend a heatpump clothes dryer......

    Winston

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  2. The redundant system is that by code I have to provide heat to each room regardless of heating loads. the bedrooms will have baseboard heaters but they will be turned off. Apparently the observation is that they will never come on. My architects have said that typically they are seeing that people can live comfortably in a passive house for up to several days before heating becomes a concern. With less air infiltration from windy conditions (blower door test is tested at 50 Pa and 75 Pa) less random infiltration means less cold air entering the home and therefor less heating requirements. The nice thing about the wood system is that I can fire up the wood stove the day before a storm, cold spell, etc and store a huge amount of energy for heating and hot water. using a small generator, I can provide the pump power for hydronic radiators and the house will be warm. We'll see. And we are planning on installing a heat pump clothes dryer in the interest of energy efficiency and not penetrating the air barrier envelope. There will be two vents through the air barrier: the HRV exhaust, and the intake.

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  3. David, as I see it, the world is in a climate change crisis, caused by fossil fuel burning,with little chance of stopping the process. The world consumes the equivalent of our Hibernia field every 14 days, and coal and natural gas is on top of that. So passive house construction is the future, if there is much of a future as to the environment. I read that Germany now has 10,000 passive houses, and that data may be old. Passive is being the standard in many areas, but so few yet.
    Your energy needs seems to be half that of a R2000. While cost effectiveness may be an issue, to make the case for passive, the environmetal challenge requires passive as necessary.
    But what the best method for passive and what is accceptable to owners is debatable, with individual choices to some extent, including lifestyles. So my preferences may differ somewhat from yours, but I am open to having my mind changed on some issues, especially subject to results.
    Now as to your wood stove......at first I thought this the cat`s meaow, but on reading the literature, I am doubtful.
    initially it looked beautiful , with the flame visible, but it looked big. It is actually about twice the size of a regular stove and some 4 ft high. It appears about twice the capacity of what your house needs, and for houses up to 5100 sq ft. 14 kw capacity with 30 percent radiant and the balance for hot water. I think you will need the insulator kit to reduce the radiant from 4.6 kw to 2.25 kw. I figure this will reduce the overall efficiency of the unit.
    With soft wood the firing rate is about 3 hrs and 5 hrs for hardwood, so it will not hold the fire overnight. That you can fire it up and heat the tank and give extended time is good........but overall, the stove, the large tank, the piping, and radiators appears to be an expensive package, if contractor installed. DO you have a figure for that.
    And what is your holiday schedule,,,,,,if gone for 2 or 3 weeks you rely on electricity or come back to a cold house taking a day to fully warm up. You may be retired, but for a working couple, is the regularity of wood burning make sense. Yet for large buildings now using wood pellets, they come with a tandem load of pellets for a hopper once every 3 weeks......so I am not knocking wood, and this is being done for modern senior complexes.
    Also the chinmey here must be 2o ft above the top of the stove, ok for you, but not so nice for a bungalow. Chimneys and air intake some 6 to 7 in diameter. New gas boilers with 60 kw capacity need only 2 inch pipes, but then, this is fossil fuel.
    I guess there is no smaller wood stove of this style with 4 inch pipes. The long chimney seems necessary for sufficent air flow , as it sucks air down . And the stove needs maintenance....cleaning.
    I think wood for temporary or back up with minisplit as still the best option,lower cost and trouble free, but you may be convinced otherwise. DO you plan for heat in your garage......is this well insulated also........why not a large window on the south garage, if this a work shop.
    Winston

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  4. Hi Winston,

    I will need the insulation kit for this to happen. I will be burning birch because of the firing rate. The system is not typical but I have other more personal sustainability goals that I want to meet with this house....including being as carbon neutral as possible. This is also one of the goals of passive house. The system has the potential to be expensive. However some of the components I will be involved in so I will offset some of the expense. As for pellets, we looked at it and thought that it could work but decided that the carbon associated with transporting pellets and what not was quite different then wood that I can get locally...and wood is always available and renewable. The tank will also have a 2000W element for times when firing is not possible. and then the hot water distribution heats the house as if we were home...with the thermostats turned down of course. This being said, my passive house designer told me about one of the houses they built for a couple that live down south for the winter. They set their thermostats back pretty far and the house has never went below 12 oC in 8 years in the middle of winter....thats pretty impressive.

    The chimney will run up through the middle of the house since keeping it internal to the envelope is much more energy efficient. the chimney will be of the larger type but I think it will fit in with the style of the house fine. I agree that the stove will need maintenance and cleaning...we'll have to see how this goes. There is another stove with a smaller pipe but it's at least 4 kW. I am dedicated to the decision at this point and like I said, i have a goal in mind for comfort and sustainability, and being as green as possible and it just works out that wood is on the list.

    So I have new elevations for the garage and there are two windows on the south wall now, none on the other walls. I am planning on installing a sliding barn door in front of the garage door to overcome some of the wind blasts penetrating around the garage door. as for heat in the garage...not sure yet I use a propane radiant heater right now and its great for a shop, sealed combustion, no moving air, great for finishing furniture! but i want to get away from the fossil fuel dependency. I am still weighting options for the garage. The garage is not included in the model.

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  5. Good improvements on your latest view. The north window on your office and alundry would be good I think on the west for solar gain, but I guess for appearance you want them where they are.
    I wonder if your west window shuld be a bit larger, even if the south a little smaller. With the sun in going down in the west it has less gain potential.
    As to shading for south upper windows, I found that 24 inch ease gives me good shade in summer and gain in winter......just run these by you for consideration.
    As to wood.......my brother burns wood all the time. By the way is 20 percent moisture content hard to get.......
    For heat for garage, or house for shoulder seasons...in case you are not aware, minisplits in winter can be COP of about 4 , and in shoulder season of about 6 (due to part load operation.....150 watt in giving about 900 watts out. This is not much realized. Also, when munted in the attic, your attic is a low grade solar collector and improves efficiency, very much so in Mar to June........you would need a wooden chimney for this to work, as I have done.
    I beleive the 12 C with no heat. My cottage room with facing south and west glass, with no heat in winter is never below 55F, while east and north room on the opposite end can go down to 40F, having a lot of glass.
    Watched a you tube video for construction with SIP panels , two story house , walls erected floor in place, roof panels all on in 4 days. Suggest 40 percent saving as to regular construction as much faster. meanwhile, your info suggest as much as 11 layers of various material for walls......seems very time consuming as to panels.
    I have an old small stove , cast iron which has a date about 1864, we used it with hard coal in the 1950s occassionally. The grates are still rally good. This stove you will use, seems to go through grates, maybe because of the downdraft and really high temp. I also seee somedata say 93 percent efficiency, elsewhere in the mid eighty I think.

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  6. Right now, we have pretty much optimized solar gain for the winter. we tried adding more west glazing has shown to increase the overheating events in the summer. There are already some overheating events in the summer time due to the slight west orientation of the south elevation.. Getting rid of some west glazing makes it better in the summer but we have to add a little more heat in the winter. Adding the shade structure has decreased overheating potential by about 80%. this is pretty good.

    yeah the efficiency of the stoves depends greatly on moisture content. I have a good supplier for the first winter and can guarantee its less than 20 percent. I plan on purchasing my first load and will stack and dry it so I am always cycling the driest stuff from my pile. Still have to work on that plan

    A mini split for the garage might be an option. Ill have to think on it. the big issues with the garage is that it will be used as a wood working shop. I have a huge dust collector but dust still make its way around. and I use flammable finishes thats why the radiant tube heater was nice. it was closed combustion to the outside. i am a little scared about a wood stove. mainly because I sometime duct my dust collector to the outside and open a window...need to find a good option here.

    The stove I plan on using get the 93% efficiency from the secondary burn chamber where hydrocarbons from the wood gas reignite when oxygen is added in that second chamber. so its pretty high temp i.e. up to 800 deg I think, but most of that heat is soaked up in the water jacket.

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  7. Looking at your data a bit more closely........your scheme is pretty good if you don mind the wood chores, but I wonder if the data reflects a bias...
    You mention somewhere else that electricity for the grid has an efficiency of about 30 percent. That may be true if all was from Holyrood. But Holyrood is only 13 percent of our energy , with 87 percent hydro. And Hydro on the island has about 5 percent transmission loss, so give that 82 percent instead of 30 percent as you suggest.
    Also wood I calculated with pellets, as to BTU, was 30 percent cheaper than baseboard, but minisplit was 60 percent cheaper than baseboard. You show a wood stove on par with with minisplit.
    The hybrid wood for space and water is good in that it provides both.....for most of the heating season. But with your insulated stove jacket, I predict you will drop 15 percent on efficiency, as all of that radiant loss will not be absorbed by the water jacket......my opinion. And I rad that wood in bags borght in cnertal USA at stores tested at 66 percent moisture.......far from dry. My may get 20 percent on second year wood if stored i your heated garage, but otherwise I doubt if you obtain 20 percent moisture......., and also do you have a intake shutter to stop the cold air entering your stove when not in use, otherwise will the stove be a ice box.....please comment.
    Your demand showing 19 kw must be all appliances on at the same time, as in our R2000 max demand with minisplits and all appliances has not exceeded 10 kw due to randomness of operation.
    I have used low temp rads for space heat on commercial that are also good for residential,
    operated down to 100F water........have you a make in mind and performance data.
    I have looked previously at the Nyle hp water heater.......appears a nice package.
    Your cost does not appears to be contractor installed prices for anything.......equipment cost I assume.
    Winston

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  8. I mentioned the inefficiency because Passive house includes it as a way to convert the site energy use to source energy use. In other words, the site may say that we use 1000 kWh but those units of energy would take an energy equivalent of 3000 kWh of oil to generate. This is a fixed number that is applicable to all of north america. The standard assumes the each man woman and child gets a fixed amount of source energy. The purpose is to minimize an individuals impact on global warming. There are nuances in the standard that are different than other standards like R2000 and netzero ready that concentrate on minimizing source energy. I agree that the software is biased but there is no option to change it if I want to certify.

    The stove jacket actually increases the stove efficiency for hot water. That efficiency is measured. with the stove jacket on, the 70/30 (hot water/air split) changes to about 85/15. the efficiency doesn't change much according to what I have seen. in the end the flue gases coming out the stove pipe are about 120 C. This is pretty low given that the temp in the burn chamber can be >800C.

    that 19 number is actually in kBTU, the number to the left of it is in kWh so the total yearly demand 12365 kWh / year and is based on fairly average loading/usage factors. The loads are harder to estimate since heating loads are instantaneous and would required minute by minute simulation with time output. the static calculation used here is great for determine energy usage though and can estimate the maximum heating load during the year.

    I have not yet made up my mind on low temp rads for the project. I am currently researching. I am open to suggestions!

    The nyle should work for this application and since its stand alone it fits nicely. given the performance, it would be like adding a solar thermal system to the tank but its now all inside the envelope and i get cooling using it.

    the intake duct will run under the slab and into the building there will be a blast gate somewhere in the mix of things. the decision on where to place it is still under question.

    the pricing is pure price at this point and I will be doing some work myself....we'll see how much!

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  9. actually its 19 kBTU/sf. I have converted it to kWh just to the right. Im not completely sure but between us we may be getting messed up in terminology here. passive house site energy demand refers to energy used. the load refers to the instantaneous energy draw in time (power). That table shows demand or total energy used. in the form of electricity. I still need to purchase the wood. but wood is considered a renewable and carbon neutral so its primary energy factor is small compared to electricity (as I mentioned before, the model penalizes energy sources based on a primary energy factor. electricity is 3.16. so for every unit used, the source energy is actually multiplied by 3.16. for wood, that factor is 0.2. the assumption is that with wood there is no processing. Its cut, its dried outside, then its burned. from this point of view there is very little embodied energy in terms of sinking man made energy into processing.


    I forgot to mention...I am woodworker...wood and moisture...a major headache. It typically takes 1 year per inch of thickness to get down to the point where the wood starts loosing water bound between the lignin. This water can typically be pushed out with heat. I recently used a solar kiln to take a piece of 3" thick elm from 180% moisture content down to 15% in 4 months. The last 15 percent took almost 2 months. But the sun did all the work! I am planning a small solar kiln for drying live edge slabs which can easily accomodate the 1-2 to 3/4 cord that I will need per year. the wood will then be stored in the porch that connects to the garage.

    BTW, as I mentioned above, if you have any ideas for rads let me know!

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  10. I assumed you were a wood worker, seeing you mentioned a dust collector and other info relating to your garage. DO you plan to constantly heat your garage, or once or twice week or whatever. I wonder your floor type and if ceiling will be insulated. High thermal mass is good, so concrete slab if steadily heated, but low thermal mass if occasionally heated, as it can heat up quickly.
    I am all for efficient wood burning, but when cut with a chain saw, pulled out with a ATV, hauled with a truck, cut with a chain saw into 14 in long pieces, split with an electric long splitter, it leavesa carbon foot print, unless you have a lot in your back yard and do all manually. For Nfld, vs electricity, especially heatpump added, the latter I suggest has a lower carbon foootprint(given the water shed forest was destroyed decades ago. But to burden the point. As wood chips and pellets is from waste from sawmill etc.....overall I would not knock wood, except where it required more attention and cannot set and forget it like electriciy heating.
    I remain sceptical on the overall efficiency of your stove....and Volkswagon cheating on performance for emmissions comes to mind. Gas furnaces rated at 95 percent efficient have temperatures leaving considerably lower and use just 2 inch plastic pipe for hot exhaust. Granted with the stove jacket, the water will get more gain, but overall reduced efficieny I expect. I have read that any moisture in wood higher than 20 percent reduces efficieny a lot. One source since 40 percent moisture reduces by 12 percent, another said up to 50 percent loss but was not specific on moisture content. You know how to dry wood....will it stay at 20 percent in the location you indicate.......is this an unheated area, and will it re-absorb moisture. But in the end if you use a cord instead of .5 cord, what the hell....I beleeive my brother in law uses 5 cords!
    Use have considered a 12,000 BTU minisplit, just for comparison. If your worse winter cold day needs 2.4 kw of heat, the 1 ton(12000 btu , which is actually cooling capaacity) will not do it. It will top out in the 1.5 to 2 kw range I suggest. And if you overload, the efficiency drops a lot. A 18-20,000 Btu will give you 3 kw of heat, and will operate at part load, so efficiency is beeter than the factory suggests. You might run that by your engineer, whether he is familiar with that aspect.
    Is your storage tank insulated. Will you heat that one tank from both the stove and nyle hp. If the tank is over 125 F from the stove source, then it is not efficient to heat further from the hp, ....the nyle will likely have a COP of 3 or 4 at low water temp, 1.5 at 120F and 2 average. When above 140 the cop may be only 1.
    As to rads. I have a few steel rads that were samples, that you could have, that may do upstairs,but wonder if needed at all up there. Others are copper tube and alum fin type that can be ordered. For low temperature water these have about 4 times normal copper and alum for heat transfer, cabint width 4.5 in, ht from 6 to 12 inch dependng on capacity. If you have btu need and quantity I can do some sizing for dimensions for you.
    Most of you prices for heating option seems very low. Example the installed price of a 12,000 Btr minisplit woulld not be less than 3000.00 plus tax. 1500 for unit and other material, and balance for labour and profit, I suggest.
    Winston

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  11. Hi David
    I do not see a few comments I sent.......I imagine if some concerns I raise you may not want to post or at least until you check things out.
    My email is ........engineeringspecialties@hotmail.com
    You can reply there if your prefer. I read the site for your architech and I assume your engineer, who is civil, and I wonder if he is up on some of the mechanical and electrical issues, .......I don`t mind sharing my experience on some of this if it helps, hopefully we all learn more as we go along.
    Winston

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