Dual fuel heat pump efficiency - need a sanity check in my logic
M&S
7 years ago
Featured Answer
Sort by:Oldest
Comments (9)
Austin Air Companie
7 years agoRelated Discussions
diff between heat pump & aux lockout temperatures in dual fuel
Comments (45)No problem and I appreciate you being ok with me bumping into your exchange here- I am following this with alot of interest. Just quickly, on my issue, the installer came back out. At first he said this was normal as shared earlier and had to be told (from a non-expert) that this was not normal at all. It seems that he made some type of wiring adjustments (unknown since my wife cant follow any of this when she was watching and asking) and then adjusted settings within the setup of the Edge Thermidisstat. We are currently running oil heated-water baseboard as the backup and then the Performance series HP system (EER 12.5, SEER 15.5 and HSPF 9) cant find the AHRI# handy. Temps have been consistently at between 28 and 34 degrees here in Viginia for the last 5-7 days. We are having to manually switch from HP to the oil heat system for right now since I dont want this installer messing with anyting else to connect a relay that allows both to be working from the one thermostat. I will do that later (hence reason for following this discussion closely) I am tracking kW useage off the meter. Here's what I am seeing: Set the HP Edge at 68 degrees and it holds house temp steady wihtout having to use AUX at all. Set the oil heat-boiler at 66 setpoint(manual) It seems that only infrequently will the boiler kick on to augment the HP (running simul right now) Energy useage has been between 3.12 and 3.77 kW per hour across last 5 days (taken in 24 hr periods). VaPOwer is at about .06 cents per kW right now I think, so I'm looking at what 744 hours per month at avg 3.44 kW (.20 cents) per hour= $153.00/month. This is for a brick ranch, 1820 sq ft house...See MoreHeat pump or AC unit w/ High efficient furnace?
Comments (9)We already have a 2 speed 18seer unit and it works VERY well. Variable speed blowers were not yet mainstream when the unit was purchased. The furnace blower has 5 different speeds, 3 of which are used. 2 for the 2 stages of cooling, and a lower one for the furnace. I realize a bit of efficiency is lost over a variable speed blower but without an inverter driven variable speed compressor, there is not much advantage to the variable speed blower. They use fixed speed setpoints anyway for the two speed condensers. My question was with regard to configuring the system as a hybrid heat pump with gas furnace instead of straigh AC with gas furnace. Can anyone answer this? Most hybrid systems place the cooling coil upstream of the furnace heat exchanger so that both heat sources can be used at the same time, in my arrangement, it would have to be either gas or hp, never both. Is it worth the $200 difference in cost or is there something else I am overlooking?...See Moredual fuel vs stand-alone heat pump
Comments (11)nash as far as nat gas,I think price will be more of a concern than supply and that the price difference between the two fuel sources will only widen. I am attaching a fuel comparison calculator for your use. I generally like straight high eff HPs with air handler and backup aux strips but with older homes not well insulated or tight envelope, then I think dual fuel is a better choice. Of course, you need a professionally performed heat/cool load calculation for correctly sizing new HVAC as well as ductwork to be thoroughly inspected for size, insulation qualities, leaks, etc. If you have any hot/cold spots in your home, now is the time to address these issues. here is a quick synopsis of Nashville climate from Trane's site. I personally think it underreports both cooling and heating but that's just my idea. anyway, it gives you an idea. Climate averages for: NASHVILLE, TN, 37203 Hot weather Cold weather Average days per year above 75: 153 Average high temperature: 88.7 Average days per year below 40: 31 Average low temperature: 36.8 I would not have a Lennox HP because of poor performance/eff numbers. Regardless of brand, you want a var speed blower whether air handler or furnace. BTW, what is the model of the upstairs HP? let me know if you have other questions. IMO Good Luck! Here is a link that might be useful: Fuel Comparison Calculator...See MoreDual Fuel Heat Pump Cost Analysis?
Comments (20)"I was under the impression that changing a heat pump's temp more than a few degrees at a time would eliminate any cost savings? Or are the newer ones more efficient and don't run long periods of time to change the temp?" What you are describing is a thermostat control issue. If you raise the temperature on a thermostat controlling a heat pump in heat mode by more than 2 degrees, the thermostat will likely turn on the auxiliary heat (electric heat strips) in an attempt to raise the temperature in a short period of time. It will do this regardless of the outside temperature. If the outside temperature is in the 40s or 50s the heat pump will be able to heat the house relatively quickly without the heat strips. This is the reason why large temperature set backs don't work well with heat pumps. The problem can be solved by having a outside temperature monitor connected to the thermostat. This would allow you to lock out the heat strips when the outside temperature is above a set level. This would allow you to set back the temperature most of the time without using additional electricity. This does have its limits since at some outside temperatures the heat strips will be needed. In North Carolina the outside winter design temperature is about 35 degrees so the heat strips are probably are not needed that often. I also use setbacks for my AC. A setback of 3-4 degrees works well for me. Anything larger has a long recovery period when the temperature is in the 90s. I personally think the smart recovery feature wastes energy. It is intended for comfort not savings. I turned off the feature on my new thermostats the week they were installed....See MoreAustin Air Companie
7 years agoM&S
7 years agomike_home
7 years agoM&S
7 years agotigerdunes
7 years agoM&S
7 years agoweedmeister
7 years ago
Related Stories
BARN HOMESHouzz Tour: An Energy-Efficient Barn Graces the Nebraska Landscape
Passive-house technologies and a rain-harvesting and greywater system conserve natural resources in this weekend country home
Full StoryLIVING ROOMS8 Reasons to Nix Your Fireplace (Yes, for Real)
Dare you consider trading that 'coveted' design feature for something you'll actually use? This logic can help
Full StoryGREEN BUILDINGHouzz Tour: See a Maine House With a $240 Annual Energy Bill
Airtight and powered by the sun, this energy-efficient home in a cold-winter climate is an architectural feat
Full StoryFIREPLACESUpdated Woodstoves Keep Home Fires Burning
Better technology means more efficiency than ever for modern woodstoves
Full StoryGREEN BUILDINGHouzz Tour: Pickle Factory Now an Energy-Wise Live-Work Space
A charming but poorly insulated 1880s Philadelphia commercial building becomes a spacious energy-efficient home and studio
Full StoryGREAT HOME PROJECTSHow to Switch to a Tankless Water Heater
New project for a new year: Swap your conventional heater for an energy-saving model — and don’t be fooled by misinformation
Full StoryLIVING ROOMSHow to Convert Your Wood-Burning Fireplace
Learn about inserts and other options for switching your fireplace from wood to gas or electric
Full StorySAVING WATER11 Ways to Save Water at Home
Whether you live in a drought-stricken area or just want to help preserve a precious resource, here are things you can do to use less water
Full StoryGREEN BUILDINGZero Net Energy: A Hardworking-House Term to Know
Homes that consume only as much energy as they produce by renewable means are a goal for builders. Learn what ZNE means for you
Full StoryLIFEThe Top 5 Ways to Save Water at Home
Get on the fast track to preserving a valuable resource and saving money too with these smart, effective strategies
Full Story
mike_home