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    HVAC Performance Data and Control

    I'm attaching a set of data that shows the behavior of a HVAC system that is comprised of a heat pump and propane furnace and the controls that are provided by my specific thermostat. Each location and each system will have different behaviors, but this forms a reference point of actual collected data. The situation for this set of data is consists of a scheduled set-point transition from 60 degrees to 62 and then to 64 degrees. I do not have automation with the thermostat (Bryant Evolution) so the specific setpoint data is not shown on the graph. I do know that the thermostat does ramp the setpoint over a 90 minute interval rather than using a step function. This type of control is much better for multistage furnace and even more so for heat pump which does not have BTUs to support rapid changes.

    The temperature data shown consists of the following:
    Pagoda (Blue) - Outside
    Nook (Green) - Thermostat
    Air Return (Teal) - Return air duct at top of furnace. This is the source air from which the heat pump or furnace will be heating
    HVAC Exhaust (Orange) - Exit of heat exchanger. This is the temperature that enters the distribution system. The delta between it and "Air Return" is the energy added by the heat pump or furnace.
    HVAC Register (Pink) - Exit of most remote duct of where heated air enters the room. The delta temperature between it and the "HVAC Exhaust" is the loss of energy through the distribution ducting. In my case it is R8 insulation going through temperatures typically at 45 degrees and total run is about 50 or 60 ft.
    Heat Pump (Red) - Entry of Puron into the heat exchanger from the heat pump. Line is about 30 ft from compressor with foam insulation through typically 45 degree space.

    At 2:00 PM the heat pump cycled for a short 20 minute period to maintain the 60 degree setpoint.
    At 3:00 PM the heat pump ran for about 10 minutes in 1st stage then kicked up to 2nd stage until 62 degree set-point reached.
    At 3:40 PM the heat pump ran for about 10 minutes in 1st stage then in 2nd stage until 5:00 PM.
    At 5:05 PM the furnace engages 1st stage for about 30 minutes. Note the "HVAC Exhaust" temperature changes from 95 degrees for heat pump to 130 degrees for furnace 1st stage. Note also the "Air Return" slope is higher due to the increase in energy transfer for furnace vs. heat pump.
    At 5:30 PM the heat pump restarts to maintain the 64 degree temperature that was achieved with the help of the furnace.
    Attached Files
    Last edited by Michael McSharry; January 18, 2011, 10:12 PM.

    #2
    Michael,

    This is interesting data particularily since I am planning to replace my heating system this year with a geothermal heat pump/propane furnace.

    What I find interesting is how the propane furnace turns on in order to bring the temperature up more quickly. If I understand correctly, the furnace turns on in response to a 2-4 degree set point increase. I am assuming the furnace would not turn on if a constant set point of 64 degrees is maintained and the outside temperature stays around 40 degrees.

    So using a set back thermostat in your situation would increase the amount of propane used compared to just leaving the T-stat at a constant temperature. I wonder if one could calculate the break-even point based on outside temperature (HDD - heating degree days) versus the number of hours and degrees of setback.

    Here in Michigan, the furnace will run a lot (outside temperature is almost always less than 25 this time of year). But there should still be some optimal amount of set back to achieve maximum energy savings.

    What would really be sweet would be to let Homeseer calculate the optimal amount of set back to apply based on outside temperature and prehaps the forecasted temperature.

    Steve Q
    HomeSeer Version: HS3 Pro Edition 3.0.0.368, Operating System: Microsoft Windows 10 - Home, Number of Devices: 373, Number of Events: 666, Enabled Plug-Ins
    2.0.83.0: BLRF, 2.0.10.0: BLUSBUIRT, 3.0.0.75: HSTouch Server, 3.0.0.58: mcsXap, 3.0.0.11: NetCAM, 3.0.0.36: X10, 3.0.1.25: Z-Wave,Alexa,HomeKit

    Comment


      #3
      This is a situation where external logic likely could save some money. One needs to get a handle on the BTU/Hr capability of the heat pump vs. the heat loss. The heat loss would be a factor of time of day, forecasted outside temperature and state of items that affect the heat loss (e.g. window shades). The setback temperature would be dynamic to always assure that the heat pump's BTU's would be sufficient to arrive at the desired temperature at the time the setback is no longer desired.

      In WA the electricy cost of $0.10/KWH is low compared to the Propane of $2.50/gal. My 9.7 HSPF heat pump in 2nd stage uses abut 4KW/H and produces 1/3 the BTU of my furnace in 2nd stage. If I run the heat pump for 3 hours it costs 3*4*0.1=$1.20 while if I run my furnace for 1 hour it costs $2.50 so I have about a 2:1 preference for using heat pump vs. furnace. I have not run the numbers, but intuitively this tells me that my setback should only be done on mild days where the needed BTUs to recover from the lower temperatue can be delivered by the heat pump. The dynamics of this calculation is too much for a typical thermostat but could be done somewhere like HS.

      My thermostat has quite a bit of flexibility in tweaking the control algorithm, but it does place limits. The one that gives me the greatest angst is a maximum of 60 minutes heat pump run time for furnace lockout before the furnace is engaged. It also has a maximum 5 degree delta for which the heat pump will be used. This means that if the heat pump cannot reach the desired temperature in 60 minutes then the furnance will start. It also means that if a large setback is used and the room temperature does go down to the setback then the furnance will be guaranteed to run. These type of control limits are fine to maximize comfort, but dont work as well to maximze cost saving.

      With the geothermal at your location you will be able to run the heat pump with low outside termperatures. In my case I set the balance point at 35 degrees. You just need to be certain that your control will provide the desired behavior to achieve your desired objectives and that the unit is sized properly to work with the type of control you are expecting to be able to use. If you are basing a purchase decision on cost savings, then you do need to consider that your setbacks cannot be as large as you now have. The "30%" savings advertised for using setback thermostats will not be possible. This is likely something the sales folks omit.

      Comment


        #4
        My energy costs are about the same as yours. But I am also on a peak billing program where my Electricty cost is $.16 /KWhr from 3-7 PM. So it will be quite complicated to figure out how to handle the setback during these hours. Right now, the more my propane furnace runs, the more it costs. So any kind of setback will save money.

        I forgot about being able to run the geothermal heat pump at temperatures below 35. I guess I could use the heat pump exclusively until the BTU heat loss of the house exceeds the BTU output of the heatpump. At that point the furnace would have to kick in.

        I was not aware the heatpump was required to run for a fixed amount of time (60 minutes in your case) before the furnace is allowed to run. I assume this is part of the control logic built into the system. Is this true even when the t-stat is changed from 60 to 70 degrees?

        My big question now is, what kind of thermostat will give me the most flexibility (via Homeseer control). In my area the choice of HVAC contractors is limited. None of them have a clue about home automation/computer controlled t-stats. I'm pretty sure I will hear," You have to use XYZ thermostat; we can't warranty anything else".

        Steve Q
        HomeSeer Version: HS3 Pro Edition 3.0.0.368, Operating System: Microsoft Windows 10 - Home, Number of Devices: 373, Number of Events: 666, Enabled Plug-Ins
        2.0.83.0: BLRF, 2.0.10.0: BLUSBUIRT, 3.0.0.75: HSTouch Server, 3.0.0.58: mcsXap, 3.0.0.11: NetCAM, 3.0.0.36: X10, 3.0.1.25: Z-Wave,Alexa,HomeKit

        Comment


          #5
          I built my system comprised of 3 zones with 3 small 24 SEER heatpump units and a single 95% efficient natural gas furnace.. one central blower.. and dampers on the returns and supplies.. as well as a 500 CFM "economizer" outside air feed for cooling or air freshening....

          each heat pump is variable speed compressor, variable speed outdoor fan and electronic expansion valve.. with each coil being located close to the zone it is conditioning very little heat loss (or heat gain) is incurred in the ductwork..

          each heat pump's own controller is designed to maintain a middle coil tube temperature of 115 at 20 degrees and below outside.. down to a 105 degree middle pipe temperature at 50 degrees outside and above..

          by varying the amount of airflow over each coil (dampers and precise main blower speed control.. as well as static pressure measurement).. I can effectively control the heatpumps themselves.. as they will work to maintain the above coil temperatures regardless of the airflow I push over the coils...

          Inverter type heatpumps are Most efficient when running at less than 80% of their rated max frequency...

          the gas furnace has a modulated gas valve that I control based on what I need in the way of heat... I never run both the heatpumps and the gas heat at the same time.. since the gas heat is 95% efficient I change over below 32 outside temperature.. or anytime below 42 when i need more than a 4 degree rise to reach setpoint...

          since I designed and installed the system my fuel bills have plummeted and comfort level has gone way up.. i am able to maintain with forced air..the same comfort level acheived by that of water heat.. with a big cost savings over water heat.. as well as do a really good job with summer cooling and humidity removal...

          I would Love to figure out a way to graph my system performance and energy usage to see if i can further optimize the system for maximum comfort and energy savings.. I dont know where to start...

          http://www.cadillackid.com:88 gives you an idea of what temperatures and parameters I monitor...... as well as the screen below...
          -Christopher
          Attached Files
          PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

          Comment


            #6
            Christopher,

            Very nice system! Very impressive monitoring and control system.

            For me the bottom line for HVAC is the operating cost. Of course, comfort is a big issue, but it is very subjective and my wife and I rarely agree on "what is comfortable". Since you have a zoned system you have the ability to provide different comfort levels in different parts of the house; that is really great.

            In terms of a graphic presention of HVAC, I primarily look at power consumption (electricity and gas(propane)). I have current transformers on my AC compressor, furnace fan, ceiling fans, and auxilliary electric baseboard heaters. Right now, I am looking at graphs from each of these HVAC items in a qualitative way to see how often they are running and how much power they are using relative to other items in the house. Below is a sample graph. This is very helpful when it comes to seeing the impact of changing a setback from 65 to 60.

            I also monitor the total Heating BTUs that I use (electric versus propane) in a more quantitative way. See Graph below. This data is calculated based on the ON time for the furnace and electric heat. I have 3 years of data.

            These are a few ideas; I'm sure you can improve on them.

            Steve Q
            Attached Files
            HomeSeer Version: HS3 Pro Edition 3.0.0.368, Operating System: Microsoft Windows 10 - Home, Number of Devices: 373, Number of Events: 666, Enabled Plug-Ins
            2.0.83.0: BLRF, 2.0.10.0: BLUSBUIRT, 3.0.0.75: HSTouch Server, 3.0.0.58: mcsXap, 3.0.0.11: NetCAM, 3.0.0.36: X10, 3.0.1.25: Z-Wave,Alexa,HomeKit

            Comment


              #7
              what hardware and plugins do you use to monitor your electricity usage?

              I could see monitoring each heat pump separately.. and then being able to come up with the exact best efficiency to run them.. doing similar to what you do.. logging degree days, outside conditions inside conditions ,etc..

              I love it!!

              how do you monitor natural gas usage? are there transducers readily available for that? with electric heat or an on / off type gas furnace it would be easy for me to measure BTU output..

              for my heatpumps I have to calculate it by knowing what my static pressure is, size of ducting, and temperature difference from air to coil, i can calculate that im pushing so many BTU into each zone...

              Most people's use of a zone system is to equalize temperatures throughout the house.. mine is unique and that my roommate and I would rarely ever agree on a temperature.. so I zoned for that reason... well and just to see if i could build it..

              if I knew the amount of natural gas flowing through the lines i could actually calculate whether im increasing or decreasing efficiency pf the furnace by modulating the gas valve.. and at one point...

              I never thought of using NWS degree-day data like you do to track.. thats a great idea!..

              and once I introduce Solar into the Mix I want to be able to find out how much money it really will save me (or cost me)..

              great stuff!

              -Christopher
              PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

              Comment


                #8
                Christopher,

                I am not using any Homeseer plug-ins for electricity monitoring. Several years ago I designed some small circuit boards that use a CR3110 current transformer to send data to my xAP network or to a DS10A. For example, on my electric baseboard heaters the CR3110 senses when the heater turns on and sends a signal to my xAp network which then tells homeseer the heater is ON. I use a script to log this information. Each morning, Homeseer runs an Excel spreadsheet that analyzes the log data and adds up all the ON time for all the heaters and calculates the number of KWhrs used. The current monitors on the various circuit branches in my house use a DS2438 to output voltage (which is proportional to current) to my xAP network. I collect this data via xapmcsdatabase. The graphs are created by Excel.

                I monitor my natural gas usage in a similar manner. My furnace controller board has a "humidifier" output that sends a signal to the humidifier whenever the burner is ON. I have a DS10A connected to this output. Homeseer keeps track of the furnace ON time. Again I use an Excel spreadsheet to add up the ON time and calculate the total BTUs output by the furnace. This is not necessarily a highly accurate way to measure gas consumption but it works quite well. I use the same approach for my gas fireplace. Since you are using a modulating gas valve, I don't think this approach will work for you. But you might be able to count the pulses via an xAP pulse counter. There are some forum threads about gas/water pulse metering devices.

                Regarding "heating degree days"; I spent a lot of time on the NOAA website researching this. It took me a while to figure out how to use this information. One thing I discovered about HDDs is they do not take into account the "wind chill factor". My house is situated at the bottom of a hill. It is protected from the wind except when the wind is from the East. When the wind blows from the East, the BTUs lost (i.e. the BTUs needed for heating) goes way up. Therefore in my BTU vs HDD graphs, I apply a "wind chill factor" when the wind is from the East (E, ENE, ESE, etc.) I use the wind chill data from the National Weather Service.

                I am also interested in Solar and I installed my first Panel (photo-voltaic) last summer. Not sure where I will go with this. My biggest learning so far: the output of the solar panel here in Michigan in Dec, Jan, (and I expect Feb) is ZERO. I'm not sure it is worth the effort!

                Steve Q
                HomeSeer Version: HS3 Pro Edition 3.0.0.368, Operating System: Microsoft Windows 10 - Home, Number of Devices: 373, Number of Events: 666, Enabled Plug-Ins
                2.0.83.0: BLRF, 2.0.10.0: BLUSBUIRT, 3.0.0.75: HSTouch Server, 3.0.0.58: mcsXap, 3.0.0.11: NetCAM, 3.0.0.36: X10, 3.0.1.25: Z-Wave,Alexa,HomeKit

                Comment


                  #9
                  Originally posted by Steve Q View Post
                  Christopher,
                  but it is very subjective and my wife and I rarely agree on "what is comfortable".
                  so, you are wrong more often then not?

                  :-)

                  --Dan
                  Tasker, to a person who does Homeautomation...is like walking up to a Crack Treatment facility with a truck full of 3lb bags of crack. Then for each person that walks in and out smack them in the face with an open bag.

                  Comment


                    #10
                    good stuff!!.. in fact great stuff!!.. I found recently that i can intercept the data on the heatpumps that goes from the main outdoor processor board to the drive board.. very simple RS-485 connection.. so i can see what the compressor command rate is and also the outdoor fan command.. however since electricity usage varies greatly with head pressure i still need to monitor power usage.. im probably going to go wit ha commercial device for this.. not that I dont build my own boards.. but when it comes to getting near high voltages I like to be sure ive got it right...

                    as for what im looking to do with solar at first is "pre=heat" the house during unoccupied times or pre-heat the return air in occupied times..

                    the idea being a bank of solar water (glycol) heating boxes.. and an electric solar panel enough to run a small pump that would push the glycol solution into a 2 pass coil in the return plenum of the gas furnace..

                    an ECM fan motor on equalization cycle uses very little electricity and would push some heat into the house.. presumably all zones during unoccupied status.. during occupied status the glycol coil would simply temper the return air before it entered the heat cycle..

                    even in dead of winter solar energy can be amazing for heat.. even just laying Black painted Plywood behind the heat pumps at the back of the house makes a huge difference in how much heat output I get for a commanded compressor frequency...

                    the modulating gas valve is a big issue for measurement as i really dont have any idea how many BTU output I get other than when its on max opening im getting the rated 80,000 BTU of the furnace as inout BTU.. output efficiency of a condensing furnace relies a great deal on the amount of water you condense out of the exhaust in the secondary heat exchanger.. get that secondary heat exchanger too warm by too much flame and not enough airflow and the efficiency goes right down the tubes.. (or out the flue)..

                    so I have to watch the exhaust temperatures pretty close..

                    the other whammy is if you drop the flame burn too low the air temperature feels cool to the occupants.. and so the thermostat gets turned up higher.. defeating the purpose of efficiency.. LoL..

                    however the difference between a 92, 95, and 98% effcient furnace seems to just be the size or number of passes in the secondary heat exchanger.. unfortunately United states AFUE ratings dont take into account the extra electricity that is needed to run a bigger blower motor when dealing with larger or more-pass heat exchangers..

                    I honestly think you and I take more tests and readings on our HVAC than the factories do when manufacturing the equipment....

                    -Christopher
                    PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

                    Comment


                      #11
                      Christopher,

                      Great discussion, HVAC is a fascinating subject; especially when the temperature outside is 4 degrees and the wind chill is -13!

                      I think the Brultech 1240 is a good off-the-shelf unit. Although I have no experience with it. The only thing available when I built my first current sensor was the Kill-a-watt. There are more offerings now. Also, don't forget about your power company. I have a smart meter on my house and my power company puts the data on its website. I can check my my usage on an hourly basis. Although the data is usually a day or 2 behind, it can be helpful.

                      I am also thinking about using solar to preheat the water to my water heater. I use well water, it is very cold. I like the idea of a glycol heat exchanger, but I have extremely limited space and the plumbing is a major engineering challenge! Another idea I have been thinking about is to use a small solar powered water pump (in the summer time) to pump warm water from a nearby pond into an insulated holding tank and use that tank as the heat sink for a geothermal heating unit. Perhaps too ambitious but its fun to consider how to better utilize the natural resources that are available!

                      Not sure how you could monitor your gas usage. Perhaps you could calculate the BTUs output from the furnace based on plenum and flue temperatures. I'm sure Michael McSharry could provide some ideas. This approach might not be extremely accurate, but it could still provide lots of information about how various scenarios impact HVAC efficiency.

                      Steve Q
                      HomeSeer Version: HS3 Pro Edition 3.0.0.368, Operating System: Microsoft Windows 10 - Home, Number of Devices: 373, Number of Events: 666, Enabled Plug-Ins
                      2.0.83.0: BLRF, 2.0.10.0: BLUSBUIRT, 3.0.0.75: HSTouch Server, 3.0.0.58: mcsXap, 3.0.0.11: NetCAM, 3.0.0.36: X10, 3.0.1.25: Z-Wave,Alexa,HomeKit

                      Comment


                        #12
                        Originally posted by drozwood90 View Post
                        so, you are wrong more often then not?

                        :-)

                        --Dan
                        Of course, I am always wrong! I just say the magic words "Yes Dear!"

                        Steve Q
                        HomeSeer Version: HS3 Pro Edition 3.0.0.368, Operating System: Microsoft Windows 10 - Home, Number of Devices: 373, Number of Events: 666, Enabled Plug-Ins
                        2.0.83.0: BLRF, 2.0.10.0: BLUSBUIRT, 3.0.0.75: HSTouch Server, 3.0.0.58: mcsXap, 3.0.0.11: NetCAM, 3.0.0.36: X10, 3.0.1.25: Z-Wave,Alexa,HomeKit

                        Comment


                          #13
                          Originally posted by Steve Q View Post
                          Michael,

                          I wonder if one could calculate the break-even point based on outside temperature (HDD - heating degree days) versus the number of hours and degrees of setback.

                          What would really be sweet would be to let Homeseer calculate the optimal amount of set back to apply based on outside temperature and prehaps the forecasted temperature.

                          Steve Q

                          This is something I have been wanting to attempt for quite some time. You mentioned in another post and I agree - wind would play a role in this as well. I know there's potential here - just have to find the time and do some planning.

                          Brian

                          Comment


                            #14
                            Just have to pop in and state that this is the coolest thread. This inspires me to do so much more with my own HVAC system. Thanks, all!

                            Comment


                              #15
                              Originally posted by Steve Q View Post
                              Christopher,

                              Great discussion, HVAC is a fascinating subject; especially when the temperature outside is 4 degrees and the wind chill is -13!

                              I think the Brultech 1240 is a good off-the-shelf unit. Although I have no experience with it. The only thing available when I built my first current sensor was the Kill-a-watt. There are more offerings now. Also, don't forget about your power company. I have a smart meter on my house and my power company puts the data on its website. I can check my my usage on an hourly basis. Although the data is usually a day or 2 behind, it can be helpful.

                              I am also thinking about using solar to preheat the water to my water heater. I use well water, it is very cold. I like the idea of a glycol heat exchanger, but I have extremely limited space and the plumbing is a major engineering challenge! Another idea I have been thinking about is to use a small solar powered water pump (in the summer time) to pump warm water from a nearby pond into an insulated holding tank and use that tank as the heat sink for a geothermal heating unit. Perhaps too ambitious but its fun to consider how to better utilize the natural resources that are available!

                              Not sure how you could monitor your gas usage. Perhaps you could calculate the BTUs output from the furnace based on plenum and flue temperatures. I'm sure Michael McSharry could provide some ideas. This approach might not be extremely accurate, but it could still provide lots of information about how various scenarios impact HVAC efficiency.

                              Steve Q
                              I wish AEP would put a smart meter on my house.. however my neighborhood even though brand new seems to be at the "end of the line" on all new technology.. so we get very little in the way of the latest stuff until last and its 4 generations back...

                              im leaning towards the brultech systems as they look easy to get set up and running.. im also finding that there are natural gas transducers out there with output of either MODBUS or standard pulse out which is easy to measure...

                              I have a few extra heatpumps in my basement to play with the idea of geothermal and how to measure their energy usage and such..

                              there is a lot to be done i think with free energy and HVAC / domestic water...

                              the trick is to make it all work and not spend too much money to save just a little money...

                              unless the idea would be to make a 'super green' house in which to be featured in mags and on TV.. then you could make more than it cost.. LoL..
                              -Christopher
                              PerfecTemp - the Most advanced HVAC system I've ever Built - and its in my House

                              Comment

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