Hobby_Man22
Well-known member
How do these work? Around here when it's not 100 degrees outside the hvac systems are usually oversized when it's only 60 degrees outside. It may turn on and run for only 7 minutes and shut off.
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Are 2 stage hvac systems complex?
- Thread starter Hobby_Man22
- Start date
You talking A/C or heat? Or both?
I have two stage heat in my HVAC systems in the house. Most of the time only the 1st stage is used, but when it is really cold (or when you spike the thermostat) the 2nd stage kicks in, along with it a higher blower fan speed.
I have two stage heat in my HVAC systems in the house. Most of the time only the 1st stage is used, but when it is really cold (or when you spike the thermostat) the 2nd stage kicks in, along with it a higher blower fan speed.
If you are talking about heat pumps. Two-stage cooling means the air conditioner or heat pump has a compressor with two levels of operation: high for hot summer days and low for milder days. Since the low setting is adequate to meet household-cooling demands 80% of the time, a two-stage unit runs for longer periods and produces more even temperatures.
For propane/ natural gas furnace. A 2-Stage Furnace is a Condensing Furnace that has two levels of heat output: ... High Output at 100% of full heating capacity, for the coldest winter days. When Low Output mode is insufficient, the furnace will automatically switch to High Output mode in order to maintain your comfort.
For propane/ natural gas furnace. A 2-Stage Furnace is a Condensing Furnace that has two levels of heat output: ... High Output at 100% of full heating capacity, for the coldest winter days. When Low Output mode is insufficient, the furnace will automatically switch to High Output mode in order to maintain your comfort.
Today with variable speed drives the compressors have inverters that can change the speeds -- this works very well with rotory compressors. The two stage scroll unit work a bit differently.
Tow stage equipment was the earliest -- two stage heat has been around for a long time -- 40 years. Two stage AC/Heat pumps have been common for around 20 years. Early ones prior to that time period required two separate compressors ($$)
The goal with all of this is to match the load ..... in heat matching the load get comfort --- in AC you get proper humidity control.
With two stage equipment it was easy to make multi-speed fan motors to match the speeds. As things got more complex there was a need to move to variable speed fan motors to match output .... one of the first was a furnace with 10 stages. Then companies developed thermostats to work with the equipment. In most of the better equipment you have to use the manufacturers thermostat .... it know the equipment and the inside and outside temps and humidity.
Two stage equipment is very common today --- in many states the rebates have made single stage more expensive. That's the case in NJ --
Tow stage equipment was the earliest -- two stage heat has been around for a long time -- 40 years. Two stage AC/Heat pumps have been common for around 20 years. Early ones prior to that time period required two separate compressors ($$)
The goal with all of this is to match the load ..... in heat matching the load get comfort --- in AC you get proper humidity control.
With two stage equipment it was easy to make multi-speed fan motors to match the speeds. As things got more complex there was a need to move to variable speed fan motors to match output .... one of the first was a furnace with 10 stages. Then companies developed thermostats to work with the equipment. In most of the better equipment you have to use the manufacturers thermostat .... it know the equipment and the inside and outside temps and humidity.
Two stage equipment is very common today --- in many states the rebates have made single stage more expensive. That's the case in NJ --
The thing to watch for on two stage is the spread in firing rate. I have seen two stage furnaces that were 100kbtu max and the low fire was 70-80k. You may as well call them single stage. If I was looking at a 100k furnace I’d want a 40-50 k low fire. It will likely run on low 90% of the time.
Most two stage furnaces I am aware of are about 70% on low fire. I am not aware of any that go lower.The thing to watch for on two stage is the spread in firing rate. I have seen two stage furnaces that were 100kbtu max and the low fire was 70-80k. You may as well call them single stage. If I was looking at a 100k furnace I’d want a 40-50 k low fire. It will likely run on low 90% of the time.
Now fully modulating it different. I have a Ruud mod furnace in my house and it will run at 40% on low fire.
It was quite a learning experience when I installed the Ruud. I suspected it was too large, but better than the 80,000 BTU I took out, plus it was modulating, it should just run on low fire if needed. After I installed it is didn't seem to modulate at all. It should run a long time on low fire to heat the house, it would turn on, then shut down in a few minutes. It did keep the house at set point. Finally, one day I decided to try something. I can set the furnace for two stage, low fire at 40% and high fire, 100%. It had heated my house for years on low fire, 24,000 BTU input, about 22,800 output. I never connected second stage until a couple years back and we had -35F a few times, then it would not keep up. I disconnect the second stage wire unless I need it.
My house it the standard 1950's rambler. I have blown a bunch of insulation in the attic, and lately resided and replaced the windows, but the wall insulation is pathetic at best. In hind sight I should have stripped all the wall board off and re-insulated the walls from the outside, then probably used 1" foam for exterior wall board, then resided.
This is the problem with the scroll compressor .... the two speeds are not far enough apart. I'm sure they are working on the problem -- but, the design is a challenge for VS. The rotary has 25% -- with no problem.The thing to watch for on two stage is the spread in firing rate. I have seen two stage furnaces that were 100kbtu max and the low fire was 70-80k. You may as well call them single stage. If I was looking at a 100k furnace I’d want a 40-50 k low fire. It will likely run on low 90% of the time.
Full VS with gas valves has made the newest stuff able to go very low as well ... There is a point to having a properly sized boilers -- some of the condensing units work best a bit oversized id in steady very cold temps ... you want that baby to condense.