OK so the mini split thing is a kind of good idea.. I bought 4 Rheem 96%EF modulating furnaces with EC blowers (DC Variable speed) 60K BTU output each furnace. and a 20 seer Rheem 2 Ton modulating Condenser (variable from 20% output to 100% in 1% steps) and a set of High Efficiency coils with housing included for 4000.00 USD delivered. the AC was 1000 and the coils were 200 600 for each furnace.. so at 1200 that's pretty darn cheap for a 20 seer AC. the mini split probably cost ya a little bit more then that.
I wanted to throw something at ya that I built.
I used a simple Arduino Uno and 6 thermisters and an ethernet shield for the Arduino
I used 2 thermisters for each of my 3 furnaces. I put one into the intake plenum before the filter. and the second went in the output plenum about 12" from the exchanger but out of direct view of it. wired them up to the Arduino. I collect input and output temperature readings. get the difference between the 2 (delta-t rise). If you look on the label inside the door on your furnace it will tell you what the max delta-t rise is for the furnace. I plug this number into the program.. and presto I now have notifications of when my filters need to be changed. This is a real world thing and not based on a length of time. It all depends on how much dust and dirt if floating around in the house.. so say if I am doing some construction work I would have to change my filter more often. This tells me exactly when it needs to be replaced.
if (out_temp - input_temp) >= max_delta_t_rise - 1:
trigger a notification
I have mine set up to send me an sms text message to my phone to change the filter.
The reason why this works is because when the filter gets clogged up the air moving through it slows down. and this slow moving air takes longer to cross the heat exchanger providing more time for the air to collect heat. if that temperature gets to high the furnace will short cycle.
One of the things I want to be able to do when i finally get around to going full tilt into writing the software to interface with ClimateTalk is I am going to add an outdoor air temp sensor. I am then going to code in a learning routine so it will know how long the temperature is going to take to drop in my house. I want to design the thing so the furnaces never turn off. I want them to stay running all of the time.
you may think that is bonkers.. So take this math.
a good furnace cycling time is 4-5 times an hour and it should run for 7-10 minutes each time.
so call it 4 times an hour at 8 minutes runtime.
some rounding and that's 30 minutes out of every single hour the furnace is going to run for,
100K btu furnace. this is going to consume 50K btu's of heat energy per hour.
so if i run a furnace at 50% for the whole hour there is no additional cost.
benefits are 1/2 as loud.
no fluctuation in the temperature in the house
less wear and tear on the furnace.
It's funny how the math actually works. because when a conventional furnace turns on it is running at 100%. it has to heat the house by usually 4 degrees. when you set the thermostat to a temperature it will not turn a furnace on until it is 1 - 2 degrees below that set temperature. there is also a "warmup time" for the furnace.. so lets make the number an event 2.. well the same thing applies when it turns off. it somewhere between 1 and 2 degrees above the set temperature..
If the furnace is running all of the time you are not making 4 degree swings in the temperature. so if the furnace is running all of the time you would need to set it to output a lot less then 50%. this is where that outside temperature helps in the calculations. that outside temp is what is going to dictate the btu output. You can do it without also by sampling the temperature in the house measuring the time it takes for the temperature to change and make adjustments according to that. I would use a combination of both.
also EC motors become more efficient the slower the speed they are at.. so you have electricity savings as well..
I had to install 3 furnaces because they do not make a high efficiency furnace that outputs over 120K BTUs unless you go commercial. plus my house is 3 stories tall and i got tired of having 3 different climates in my house. the original furnace was to small for the home and the ductwork was completely wrong. They had a single return for the furnace and 7 registers 4 of the 7 registers were 3" ducts and the rest was 6". my house is almost 3000 sqft poor insulation (r7 walls, r19 roof no attic). now I have 24 registers 19 of them have 6" ducts. and the rest are 4" they are all insulated rigid ducts. I also have 9 returns one in each bedroom and the rest scattered about the house. my gas consumption dropped by 50% from the old furnace which was a 120K btu. where as I am at 180K now. now my furnaces actually turn off when it's -20F (-29C) outside.
OK so the mini split thing is a kind of good idea.. I bought 4 Rheem 96%EF modulating furnaces with EC blowers (DC Variable speed) 60K BTU output each furnace. and a 20 seer Rheem 2 Ton modulating Condenser (variable from 20% output to 100% in 1% steps) and a set of High Efficiency coils with housing included for 4000.00 USD delivered. the AC was 1000 and the coils were 200 600 for each furnace.. so at 1200 that's pretty darn cheap for a 20 seer AC. the mini split probably cost ya a little bit more then that.
I wanted to throw something at ya that I built.
I used a simple Arduino Uno and 6 thermisters and an ethernet shield for the Arduino
I used 2 thermisters for each of my 3 furnaces. I put one into the intake plenum before the filter. and the second went in the output plenum about 12" from the exchanger but out of direct view of it. wired them up to the Arduino. I collect input and output temperature readings. get the difference between the 2 (delta-t rise). If you look on the label inside the door on your furnace it will tell you what the max delta-t rise is for the furnace. I plug this number into the program.. and presto I now have notifications of when my filters need to be changed. This is a real world thing and not based on a length of time. It all depends on how much dust and dirt if floating around in the house.. so say if I am doing some construction work I would have to change my filter more often. This tells me exactly when it needs to be replaced.
I have mine set up to send me an sms text message to my phone to change the filter.
The reason why this works is because when the filter gets clogged up the air moving through it slows down. and this slow moving air takes longer to cross the heat exchanger providing more time for the air to collect heat. if that temperature gets to high the furnace will short cycle.
One of the things I want to be able to do when i finally get around to going full tilt into writing the software to interface with ClimateTalk is I am going to add an outdoor air temp sensor. I am then going to code in a learning routine so it will know how long the temperature is going to take to drop in my house. I want to design the thing so the furnaces never turn off. I want them to stay running all of the time.
you may think that is bonkers.. So take this math.
a good furnace cycling time is 4-5 times an hour and it should run for 7-10 minutes each time.
so call it 4 times an hour at 8 minutes runtime.
some rounding and that's 30 minutes out of every single hour the furnace is going to run for,
100K btu furnace. this is going to consume 50K btu's of heat energy per hour.
so if i run a furnace at 50% for the whole hour there is no additional cost.
benefits are 1/2 as loud.
no fluctuation in the temperature in the house
less wear and tear on the furnace.
It's funny how the math actually works. because when a conventional furnace turns on it is running at 100%. it has to heat the house by usually 4 degrees. when you set the thermostat to a temperature it will not turn a furnace on until it is 1 - 2 degrees below that set temperature. there is also a "warmup time" for the furnace.. so lets make the number an event 2.. well the same thing applies when it turns off. it somewhere between 1 and 2 degrees above the set temperature..
If the furnace is running all of the time you are not making 4 degree swings in the temperature. so if the furnace is running all of the time you would need to set it to output a lot less then 50%. this is where that outside temperature helps in the calculations. that outside temp is what is going to dictate the btu output. You can do it without also by sampling the temperature in the house measuring the time it takes for the temperature to change and make adjustments according to that. I would use a combination of both.
also EC motors become more efficient the slower the speed they are at.. so you have electricity savings as well..
I had to install 3 furnaces because they do not make a high efficiency furnace that outputs over 120K BTUs unless you go commercial. plus my house is 3 stories tall and i got tired of having 3 different climates in my house. the original furnace was to small for the home and the ductwork was completely wrong. They had a single return for the furnace and 7 registers 4 of the 7 registers were 3" ducts and the rest was 6". my house is almost 3000 sqft poor insulation (r7 walls, r19 roof no attic). now I have 24 registers 19 of them have 6" ducts. and the rest are 4" they are all insulated rigid ducts. I also have 9 returns one in each bedroom and the rest scattered about the house. my gas consumption dropped by 50% from the old furnace which was a 120K btu. where as I am at 180K now. now my furnaces actually turn off when it's -20F (-29C) outside.