PV energy less expensive than natural gas.

[cdev]

Water will condense under the core in the winter and it will need to be conducted into a drain or outside in a way that doesn't/can't freeze shut. We have a little tube that goes down to the basement laundry sink. For me there is usually very little water but the climate where I live (East Coast US) is very mild compared to Canada where you live. The HRV keeps the house warm and even in the winter the air coming in is warm enough to not be a shock, its cool but not cold at that point, when its well below freezing outside. I mean to set up a set of sensors so I can have some numbers on its performance. I think it is definitely performing as advertised. Even in the winter nights we turn the heat way down so it only kicks in when its really really cold in the winter. I sleep better that way. The HRV keeps it warm enough in the house for that to work fine. There is enough residual heat to make the air coming in quite a bit warmer all night long. Right now its on fairly continuously at a low setting.

One thing that is non standard on mine is the unit itself is upstairs, not in the basement. I wanted the air intake and exhaust to be up high, not down low. Its cleaner and picks up much less crap. Its hanging from hooks to isolate the sound.

[cdev]

My unit has a complex controller board that manages the dampers and fan speeds. It has a expensive wall mounted controller panel - an option- that I would very much like to be able to emulate - I am pretty sure it could have multiple instances on the same loop, so emulation would likely work well.

Most of the time we just are using it all the time but we change the settings for speed and duty cycle (time on vs time off) to suit the weather and time of day and whether we have windows open. The reason I would like more control is that there are only three speeds and three duty cycle settings and there is no way to tell it not to operate say when its just finished raining outside in the summer and its much more humid outside than in. It understands the need to exhaust high indoor humidity but not the desire to change the program when its just rained outside. There are a few other relatively minor things that I would like it to do that it doesnt.

The controller board is made by Kanalflakt. My unit is now basically pretty old and so I have no idea what they use now. I just want to do this for myself.

[electrodacus]

Water will condense under the core in the winter and it will need to be conducted into a drain or outside in a way that doesn't/can't freeze shut. We have a little tube that goes down to the basement laundry sink. For me there is usually very little water but the climate where I live (East Coast US) is very mild compared to Canada where you live. The HRV keeps the house warm and even in the winter the air coming in is warm enough to not be a shock, its cool but not cold at that point, when its well below freezing outside. I mean to set up a set of sensors so I can have some numbers on its performance. I think it is definitely performing as advertised. Even in the winter nights we turn the heat way down so it only kicks in when its really really cold in the winter. I sleep better that way. The HRV keeps it warm enough in the house for that to work fine. There is enough residual heat to make the air coming in quite a bit warmer all night long. Right now its on fairly continuously at a low setting.

I researched about all this in the past so I know what I need to do is just the implementation that is more challenging. I also already have the input and output holes setup with thermal sensors so I can calculate the efficiency but should be in the 60 to 80% range. Still the amount of energy stored in the air is not great and thus total saving on heating are just in the 5 to 10% range compared to not using a HRV.
I also have CO2 sensor that will be used to control the amount of ventilation to keep things as efficient as possible and I will have to build my own speed controller and algorithm I'm just to busy with more urgent things at the moment and this is low priority as mentioned savings will not be that large but sufficient to worth having a HRV. 

[coppice]

I also have CO2 sensor that will be used to control the amount of ventilation to keep things as efficient as possible

You might need a more elaborate scheme that just monitoring CO2. In many circumstances it gets kinda smelly long before the CO2 rises much when you are in an enclosed space.

[cdev]

With the caveat that I have an AC-running system, which likely is quite different in philosophy and layout than a DC PV powered system, also I have a conventional hydronic heating system too, the main benefit of the HRV has been cleaner air year round, so much so that its not been musty and humid indoors in a very long time.
It also seems like to me that with this system I do save a lot of energy because in my experience, its extremely wasteful of energy to leave windows open in the winter.

Unless the heat is on, opening a window will make the entire house chilly very quickly. Contrast that to the HRV which is a fan so it moves a lot of air, not making the house cold at all. Opening a window while the HRV is running will screw up the HRV's balancing and it may get much colder depending on what window is open. It works best when all the windows are shut.

Id be interested in the different design philosophy with a PV system. I am gathering that the 150 cfm my HRV pushes is probably much more than in some zero net energy houses, hence the mustiness?

[electrodacus]

You might need a more elaborate scheme that just monitoring CO2. In many circumstances it gets kinda smelly long before the CO2 rises much when you are in an enclosed space.

From my tests CO2 is a fairly good indication. Most modern house here have a lot of bad materials like glues for carpets and badly made furniture and appliances that will constantly release a lot of nasty compounds plus some houses have leaked radon trough bad foundations and penetrations none of this apply to my house.
So yes in vast majority of standard build house is just best to set a minimum air flow around one full air exchange in 3h and do not care about other indicators but for me the CO2 detection should work well (I will see when I get this implemented and adjust accordingly).
I do not have guests often and 95% we are at home as we work from home thus CO2 rate will be fairly constant with slight variation between day and night.
It is sad that most houses are badly designed considering how much knowledge we have today about all aspects.

[cdev]

Not only do all those fake wood products emit formaldehyde in abundance, god forbid that they get more than superficially wet, do you know what happens then? (in addition to much more formaldehyde offgassing for the rest of their life- which may not be very long.)

Okay here is the answer to my question, fakje wood products that have been wet - in addition to offgassing substantially more fumes, also lose structural strength leading to a potential for sudden catastrophic failures.

One failure mode is 'delamination'

[coppice]

You might need a more elaborate scheme that just monitoring CO2. In many circumstances it gets kinda smelly long before the CO2 rises much when you are in an enclosed space.

From my tests CO2 is a fairly good indication. Most modern house here have a lot of bad materials like glues for carpets and badly made furniture and appliances that will constantly release a lot of nasty compounds plus some houses have leaked radon trough bad foundations and penetrations none of this apply to my house.
So yes in vast majority of standard build house is just best to set a minimum air flow around one full air exchange in 3h and do not care about other indicators but for me the CO2 detection should work well (I will see when I get this implemented and adjust accordingly).
I do not have guests often and 95% we are at home as we work from home thus CO2 rate will be fairly constant with slight variation between day and night.
It is sad that most houses are badly designed considering how much knowledge we have today about all aspects.

Those are all valid potential issues, but I was thinking more of the smells originating from the occupants of the house - cooking, exercising, pets, bringing something into the house which turns out to be a bad decision, etc.

[Nusa]

For amortization cost, you left out the most important factor: the investment value of that $15,000. You may be a lousy investor, so this is easiest to calculate if we treat it as borrowed money. For example, if you can find a $15000 30-year loan at 5%, you'd have 360 payments (30 years) of $81/month, for a total of nearly $29000 to pay it off. The purchase value of money would likely decrease during that period, and your income will likely rise, so it's not quite as bad as it sounds. But it's more than the $42/month you quoted, with all 360 payments paid in advance.

The number we haven't heard is what the average monthy costs were before this system was installed. That number minus your amortized cost is what determines how worthwhile this project is from the financial standpoint. If it's > 0, you're still looking good, since utility costs also will rise over time, barring a breakthrough in cold fusion or the like.

[cdev]

Utility costs may rise quite a bit in the next few years because of the export of LNG.

Because of the price rise in natural gas, electricity prices track natural gas prices, according to LA Times, so will likely also rise a lot. So PV makes a lot of sense, and will make even more sense in the near future.

[Nusa]

Coal is currently huge political button here in the US, never mind any logical arguments on either side. It's not nice to go there on someone else's thread. Let's leave it at utility prices historically rise over time, and the value of monetary units historically decreases over time.

[electrodacus]

For amortization cost, you left out the most important factor: the investment value of that $15,000. You may be a lousy investor, so this is easiest to calculate if we treat it as borrowed money. For example, if you can find a $15000 30-year loan at 5%, you'd have 360 payments (30 years) of $81/month, for a total of nearly $29000 to pay it off. The purchase value of money would likely decrease during that period, and your income will likely rise, so it's not quite as bad as it sounds. But it's more than the $42/month you quoted, with all 360 payments paid in advance.

The number we haven't heard is what the average monthy costs were before this system was installed. That number minus your amortized cost is what determines how worthwhile this project is from the financial standpoint. If it's > 0, you're still looking good, since utility costs also will rise over time, barring a breakthrough in cold fusion or the like.

This is a new house build in the middle of nowhere so offgrid. The temporary heating solution was small 8kg propane tanks that powered a thankless water heater that in turn circulated warm water trough pex tubing embedded in the concrete floor.
The cost of one of those propane tanks was around 25 to 29CAD so about 20 to US$25 and around 12 of those where needed in coldest month and around 55 to 60 of them for the entire heating season each of those barbecue stile 8kg (2lb) propane tanks have about 100kWh of energy but the heating system was just around 80% efficient.
so for a heating season I was paying about 1100 to $1200 and this was just heating it was not including the house electricity that was still provided by PV just with a much smaller PV array.
Now the combined heating + electricity is just $500/year so no doubt a huge improvement considering just the heating it may be a 4x or more reduction in cost.
Also the cost of the propane heater was not include (was cheap but failed after about 4 years) and the fact that I needed to transport those propane tanks thus extra transportation cost and inconvenience.

For a relatively save investment the 3% or so annual interest will likely not even cover the inflation.

I can give you a better way I can earn money. We drink 4liter (one gallon) of distilled water per day that up to now were purchasing at grocery store for about 2CAD  1.5USD and now since I have much more electricity I can do at home with a small distiller that uses around 3.5kWh to produce those 4 liters per day and amount of energy used is irrelevant as in winter that will still end up as heat so there is no need for extra PV panels and in summer this distiller can be outside so it will not heat up the house.
Those $1.5/day mean $547.5/year in saving thus that saving alone more than pays for the entire installation and leave my heating and electricity as free plus a $47/year bonus
There are quite a few other things that can do the same for me like I will be using a electric hand dryer to save even more on on paper towel's. Will likely get more ideas over time as half of the energy is unused and the one used in winter can have first another use then end up as heat.

[Marco]

Thermal storage in concrete costs nothing if the house is designed to take advantage of the structural concrete that is already needed as it is my case with the 14m³ concrete floor 30 tones that is also the house foundation (insulated slab on grade).

Did you add a lot of new floor insulation and use the pex tubing to circulate water to heaters on demand? Otherwise I don't see how to turn the slab's thermal inertia to thermal storage.

[electrodacus]

Did you add a lot of new floor insulation and use the pex tubing to circulate water to heaters on demand? Otherwise I don't see how to turn the slab's thermal inertia to thermal storage.

This house was designed and build by me not modifications to an old house. What you call thermal inertia is the same thing as thermal storage.
Thermal insulation will have been needed anyway if you want an energy efficient house and up to a point adding thermal insulation will be the most cost effective thing to do.
I currently no longer use the pex as I added electric heating wires (just normal silicone isolated copper wires 22 AWG to 18 AWG will work fine and they work at 30 to 33V DC no conversion just max power point from the PV array).   

[Marco]

This house was designed and build by me not modifications to an old house. What you call thermal inertia is the same thing as thermal storage.

Bit of semantics but I'd say storage should be able to tapped at a desired power output. Then it lets you set a thermostat while providing all the necessary power. A building's thermal inertia obviously only lets you save on heating if you want to set a thermostat.

[electrodacus]

Bit of semantics but I'd say storage should be able to tapped at a desired power output. Then it lets you set a thermostat while providing all the necessary power. A building's thermal inertia obviously only lets you save on heating if you want to set a thermostat.

Since delta between ambient and floor temperature is just maybe 2C the floor works as a thermal mass storage. As it is now if I stop any sort of heating and outside temperature is -5C to -10C then there will be a 1.5 to 2C loss in internal temperature over a 24h period.
Like it was overcast for the past 4 days and I started with 25.4C (4 days ago) outside temperature is around freezing few degree negative at night and maybe +1C or so max during the day and right now I have +19.9C and tomorrow should snow and be the last overcast day thus I will be fine but I will need that additional 60kWh water thermal storage to have a bit larger autonomy and a bit more constant temperature even if is hard to notice changes that are this slow like just a bit over 1C drop in 24h

[gildasd]

As an aside, I have a « D » ventilation system.
Works really well, I clean the filter with a vacuum once awhile and that is it.
I would recommend it over a B system with slotted windows.

It is self installed system from Easykit.

[f4eru]

Heat pumps are not cost effective when talking about PV solar heating as they have a limited life and fairly high cost's.

Not so fast. Depends on a lot of factors.
Heat pumps have an efficiency advantage of about 3x over resistive heating !
Heat pump for hot water + heating is a big plus in the times you don't get PV, and must get this energy from the grid. Then resistive heating is a huge bill at once !
If you reinject the overproduced PV, the energy you consume on your resistive heating is also going to lose you the amount you auto-consume at the rate you get paid for reinjection ! That may be a huge contributor when you consume 3x more.

So factoring in those 2 parameters, I think heat pump is often a huge advantage, even if it needs replacement or bigger maintenance after 15 Years.

For an approximation for hot water :  https://www.quora.com/How-can-I-estimate-the-kWh-of-electricity-when-I-take-a-shower

when you take a hot shower, you consume half a kWh per minute

- Let's say you get 8 cent/kWh if you reinject PV to the grid, and have 30min of shower/day in the house (everybody combined).
- let's say you pay 16 cent/kWh  for electricity you consume from the grid
- let's say the water heater is intelligent enough to heat and modulate the boiler only during daylight to maximize the use of the PV for hot water.
- let's say you have 40 days/Year with insufficient PV output for your hot water, you have to use the grid.

With Resistive, you'll miss 486€/Year
With Heat pump you'll miss 162€/Year

Over 15 Years, the difference is 4860€ -> that'll probably amortize the higher cost for the heat pump boiler, not sure how much those cost over a resistive boiler, somebody has a figure ?

Multiply those figures by 5 to 10 for heating of the house with resistive, it gets crazyly expensive at that point.

I have resistive heating from the grid, but it's only emergency use to avoid freezing the house when away for long periods and nobody lights the wood burner for days in the winter.

From my experience, heating the house with thermal solar or PV+heat pump is pointless if you have a good isolation and big south-oriented windows. In that case, the direct heating through the windows bring more heat to the house than the complex heating system.

This means: If you have a modern house and install solar heating, be prepared to get most of the heating energy from the grid, not from solar, be it thermal, or PV based. You basically need 90% of heat energy exactly at the times when solar is not available !
I had that lesson learned as I overdimensionned my thermal solar thinking I'll get heating from it. In retrospect it gets hot water, that's it.

Again : YMMV widely depending on a lot of local and individual factors

[DougSpindler]

Heat pumps are not cost effective when talking about PV solar heating as they have a limited life and fairly high cost's.

Not so fast. Depends on a lot of factors.
Heat pumps have an efficiency advantage of about 3x over resistive heating !
Heat pump for hot water + heating is a big plus in the times you don't get PV, and must get this energy from the grid. Then resistive heating is a huge bill at once !
If you reinject the overproduced PV, the energy you consume on your resistive heating is also going to lose you the amount you auto-consume at the rate you get paid for reinjection ! That may be a huge contributor when you consume 3x more.

So factoring in those 2 parameters, I think heat pump is often a huge advantage, even if it needs replacement or bigger maintenance after 15 Years.

For an approximation for hot water :  https://www.quora.com/How-can-I-estimate-the-kWh-of-electricity-when-I-take-a-shower

when you take a hot shower, you consume half a kWh per minute

- Let's say you get 8 cent/kWh if you reinject PV to the grid, and have 30min of shower/day in the house (everybody combined).
- let's say you pay 16 cent/kWh  for electricity you consume from the grid
- let's say the water heater is intelligent enough to heat and modulate the boiler only during daylight to maximize the use of the PV for hot water.
- let's say you have 40 days/Year with insufficient PV output for your hot water, you have to use the grid.

With Resistive, you'll miss 486€/Year
With Heat pump you'll miss 162€/Year

Over 15 Years, the difference is 4860€ -> that'll probably amortize the higher cost for the heat pump boiler, not sure how much those cost over a resistive boiler, somebody has a figure ?

Multiply those figures by 5 to 10 for heating of the house with resistive, it gets crazyly expensive at that point.

I have resistive heating from the grid, but it's only emergency use to avoid freezing the house when away for long periods and nobody lights the wood burner for days in the winter.

From my experience, heating the house with thermal solar or PV+heat pump is pointless if you have a good isolation and big south-oriented windows. In that case, the direct heating through the windows bring more heat to the house than the complex heating system.

This means: If you have a modern house and install solar heating, be prepared to get most of the heating energy from the grid, not from solar, be it thermal, or PV based. You basically need 90% of heat energy exactly at the times when solar is not available !
I had that lesson learned as I overdimensionned my thermal solar thinking I'll get heating from it. In retrospect it gets hot water, that's it.

Again : YMMV widely depending on a lot of local and individual factors

Numbers would be quite different in California.  We have time out use billing and the power company will buy electricity from customers for $0.48 kWhr and customers can but that electricty back for as little as $0.12.

[Nusa]

f4eru, you need to read the thread. The OP has already said this is an off-grid house in the middle of nowhere. The wires aren't there, the grid isn't there. If he can't use or store what his panels generate, either in battery or thermal banks, it's lost. His backup heat source is propane.

[f4eru]

OK, sorry, I missed that.
That's more critical if the grid cannot buffer, and needs really careful planning, or even an approximate model simulation for an optimal decision IMHO.
From your propane heating experience, what do you feel is the relationship between solar availability and heating need in your case ?

[cdev]

Volcanic eruption- a big one, as happens every once in a while, randomly.

What happens to PV, hydro, natural gas and other fuel prices, food availability and prices, and climate?

[Marco]

Like it was overcast for the past 4 days and I started with 25.4C (4 days ago)

So do you just wear shorts? You can get 2 1000L IBC tanks for 50 Euros here, throw on some insulation and you have 150 kWh of storage at 80 degrees Celsius which you can use with temperature control. Heated slab on the whole has never made much sense to me, you can have far superior insulation above the slab than below it and I find thermal inertia more problem than benefit.

[9aplus]

@electrodacus
Nice system and great way of limited resources use.

I am on sunny Adriatic but for 2-3 months in winter we
need heating to keep the house dry from sea moisture.
Your cheap way of direct DC floor heating may be feasible
for us too.

[electrodacus]

OK, sorry, I missed that.
That's more critical if the grid cannot buffer, and needs really careful planning, or even an approximate model simulation for an optimal decision IMHO.
From your propane heating experience, what do you feel is the relationship between solar availability and heating need in your case ?

I do not use any backup source as it will not be needed that was in the past when my solar heating system was not complete now is 100% solar heating with no backup.

As for the heat pump that will not be cost effective in any situation including grid as heat pump has a cost associated with it and a limited life (will require a few replacements over a 30 year period).
Keep in mind my system total cost was $15K and climate is fairly harsh with average temperature for January -16.7C thus an air to air heat pump will not work and a geothermal installation will cost significantly more than my entire solar system.
It is likely that even in ideal conditions a heat pump will not be cost effective in best case scenario it will just recover the investment before it needs a replacement.

The electricity generated by PV is almost free at 2 cent/kWh and thermal storage even more so with as low as 1 cent/kWh thus there is no way for a heat pump to be added and have any financial advantage as they where designed to barely break even with grid prices around 20 to 30 cent/kWh in a moderate climate.

Natural gas that can be as low as 3 to 5 cent/kWh is the closest competitor to direct solar PV heating and this only assuming house is already connected to natural gas line.

So do you just wear shorts? You can get 2 1000L IBC tanks for 50 Euros here, throw on some insulation and you have 150 kWh of storage at 80 degrees Celsius which you can use with temperature control. Heated slab on the whole has never made much sense to me, you can have far superior insulation above the slab than below it and I find thermal inertia more problem than benefit.

You can not get a standard 1000L IBC tank trough a normal size door and having this outside is not feasible as even with a lot of expensive thermal insulation loss will be fairly high plus other complications with bringing the heat inside.
Also the max temperature allowed with those IBC tanks is 60C so your max storage capacity for one of them is 1000L x 40C delta x 1.16 = 46.4kWh
There are special water tanks that can fit trough a normal door so I can get that inside (a fair bit more expensive) and since is narow and tall it will not use much space inside the house and have a 1500 liter capacity with about 60kWh storage capacity again +60C max temperature so I will use it in the 20C to 55C range 35C delta and that is also ideal range for the pex that I already have installed in the floor. No thermal insulation will be needed as temperature of the tank will be low and surface area very small so the loss rate will not be high enough to overheat the house and if needed little thermal insulation can correct the "loss" so that is in the acceptable range.

Also an important fact is that water thermal storage while great has disadvantages compared to concrete floor as it is my case where I mentioned the capacity of the floor is 97kWh that is from +18C to +30C but when you get to +18C it dose not mean your thermal storage is empty and in a few hour your house will be below freezing if is -30C outside as is often the case here as you may need about 24kWh of energy for 24h to maintain the temperature that means another 3C temperature drop so now is +15C assuming heating is broken and you just use thermal storage.
With water storage when water gets to 20C so empty is basically empty especially with a high temperature water storage and there is no extra buffer there you will just freeze

With thermal solar there is nothing to break and even if my DMPPT450 thermal controller breaks I can still directly connect the PV panels to the restive heat elements and there will be almost no difference until I can fix or replace the DMPPT450.  Reliability of the heating system is very important to me because of the harsh climate here and nothing will be as reliable as direct solar PV heating on top of that it just happens that is also the most cost effective