Backup heat for central IN

Discussion in 'General Discussions' started by Nicholas Bethard, Mar 23, 2021.

  1. Nicholas Bethard

    Nicholas Bethard New Member

    So if I'm understanding the data here right, let me summarize...

    1) For a 2 stage system (e.g., WF5), the geo+propane aux heat style makes some sense because of the difficulty in matching heating capacity without waaayy overdoing the cooling capacity.
    2) For a variable speed system (e.g., WF7), you can potentially go all geo (no aux heat) because the system can be sized for the needed heating capacity without blowing cooling capacity out of the water (and losing dehumidification effects, etc.).
     
  2. gsmith22

    gsmith22 Active Member Forum Leader

    If it was me, I would go all geo and find a heat pump maker whos equipment fit my situation better if the heating/cooling capacities of the 3 and 5 series WF units are what SShaw says (I have spent no time reading their catalog and he always knows what he is talking about so...). The only way I would consider auxiliary help to a geo system was if I had a single stage unit. But even then, my frustration with the propane system I had prior to geo would lead me to electric strip heat and a lot of solar panels to net out the energy usage with the PoCo over the year (Could always do batteries too as Noobie does back in post 12). I have 7 series WF units and have been very happy but at the end of the day, 2 stage heat pump equipment is not new tech and there are lots of players in that game. Climatemaster makes both 2 stage and variable speed. I don't really hear about their variable speed tech much though. Lots of people with CM 2 stage units on this board.
     
    SShaw likes this.
  3. Nicholas Bethard

    Nicholas Bethard New Member

    From what I understand about HP's (either AS or GS), the heating and cooling capacities are usually similar. Makes sense, as its the same system just running in different directions. That's why I don't see how a 2 stage system without any aux heat could realistically work for me.

    The 2 stage system with propane aux heat that was already quoted is based around the Tetco ES5. Tetco (Enertech) has a really cool VS GSHP, but its water to water and Enertech told him it wouldn't really make sense in a house without radiant heat. He's digging into both the WF7 and ClimateMaster VS systems. WF7 may end up being my only VS option because its the only one with a split option. My basement/crawl space is a bit odd and a big packaged unit down there may not be realistic. We'll see.
     
  4. gsmith22

    gsmith22 Active Member Forum Leader

    a ground source heat pump's capacity is highly dependent on the incoming water temperature (its not constant) and as the water temperature drops, so does the capacity. It doesn't drop nearly as drastically as an air source heat pump does with lower air temp, but its lower none the less. If you are putting in a closed loop system, I would design for incoming water temp of 30F for heating and an incoming water temp of 90F for cooling and you will need your loop to have antifreeze (methanol or ethanol, don't use PG). Closed loop systems can have big swings in their temperature. So your "4 ton" unit won't have 4 tons of heating at 30F incoming water temp - likely something less than 4tons (maybe 3.8). And it will likely have more than 4 tons of cooling at 90F incoming water temp (maybe 4.3). I believe the naming of the units comes from how they are rated by AHRI which is typically at some in between incoming water temp (which you will rarely see during either heating or cooling so their rating method is useless for actual use). Each heat pump manufacturer should have a specification booklet that gives you all of the unit capacity data at a range of incoming water temps. Use that for sizing and not the generic unit naming.

    Two stage systems can work without aux heat because they use the first and second stage for their design season (so heating for you) and then only use the first stage for shoulder seasons (heating or cooling) and summer (in cooling). But, you still get unit off/on in stage 1 (if in stage 2 it likely jumps down to stage 1 instead of turning off). But, they turn off/on less than a single speed unit would. Variable speed units run nearly constantly at very low speeds.

    A very optimized two stage system might be slightly undersized for heating (so manual J shows you need 75k BTHU and you put in 60 BTHU-5 tons). Manual J is using the historical worst (99%) heating temp so the vast majority of cold winters and all of warm winters get handled by heat pump and say 1 week every few years your system uses some electric heat at night for a few days to make up that extra 15k BTHU. Stage 1 in that system is probably around 30k BTHU so it will turn on/off a little bit during cooling season (because you only hit that cooling load 1% of the time) but its not single speed equipment cycling. Your situation isn't unique. there are lots of 2 stage systems handling it. variable speed tech only came about in 2012.

    Spec books have the physical sizes of the units so you should be able to judge space constraints before you get too far down the road. For what its worth, my units fit in the exact same space/connect to the same ductwork as the propane furnaces that were taken out.
     
  5. SShaw

    SShaw Member Forum Leader

    Here is the data I was looking at on the 5 Series. You can see the water temps used for the rating.

    The Climatemaster 2-stage GSHPs look to have higher cooling capacity than heating also. So does the WF Series 7, but WF plays some games with the rating. The compressor has 12 stages, but WF declares stage 9 as 100% in cooling operation, versus stage 12 in heating, so the output is more level.

    Regarding the WF 7 split... You'll need to look at the size data. I believe you must use their communicating SVH air handler. You cannot use a fan coil on a furnace like you could with a 5 Series. The SVH is shallower, but it's 58" tall, whereas the 3T and 4T packaged units are 4" shorter.

    Untitled.png
     
  6. Nicholas Bethard

    Nicholas Bethard New Member

    More cooling capacity than heating would be inverse of what my home needs. Hence the issue. If I end up going 2 stage, it seems like it'll need to be as I mentioned above...properly sized for cooling with propane aux to make up the difference in heating capacity. If I go GSHP only with a 2 stage, then I'm essentially buying a 1 stage AC system with 2 stage heating, which just makes no sense to me.

    Regarding VS, something I sort of mentioned by didn't reiterate when I posted my ManJ load numbers was that its TWO systems...one downstairs and one up. Plus I sorted out how to enter better details about my windows, doors, and internal loads, which altered the numbers (for the better) quite a bit...downstairs heating/cooling 42k/21k, upstairs heating/cooling 23k/18k.

    As for the size/dimensional challenge, the current downstairs system is wedged into an area that isn't really big enough for it. The plenum coming off the top is way too short and the return air ductwork is a huge mess, coming in from three different directions. We're going to clean all that up, but doing so might require the system be split. That isn't totally clear yet.
     
  7. SShaw

    SShaw Member Forum Leader

    You'd have to see what your installer thinks, but if you oversized the loop a bit to keep the EWT above 40 (or relied on AUX heat for a couple hours/year) then I think two 3T WF 7 Series should work well. If the ductwork was possible, a single 5T 7 Series split into two zones would probably work well too. At 40-deg EWT the 5T outputs 68.5K BTUH.
     
  8. Nicholas Bethard

    Nicholas Bethard New Member

    Zoning upstairs/downstairs is a cool idea, but would mean eating the majority of a closest to get from basement/crawl space to the upstairs attic. The original house plans had the upstairs mechanical closet directly above a large chase going down to the basement, but the builder decided instead to make the upstairs bathroom insanely large and put the mechanical closet elsewhere. Shucks.

    I think the idea right now is probably 4T down/3T up since 3T is the smallest they make for WF7. And as mentioned also looking at the CM Trilogy, but difficultly wrangling a horizontal unit into the crawl space may negate that option. Plus if we put a package unit upstairs, its water lines would be going through unconditioned attic space.

    I also have another building with a third system we were planning to just do a midline ASHP+propane furnace in. I need to do the ManJ for that building and then do the math to see if there's any financial sense in looking at geo over there. Yeesh.
     
  9. Nicholas Bethard

    Nicholas Bethard New Member

    Ending up with three ClimateMaster Trilogy systems, all sized for full heat load of their respective spaces. Propane usage on the property will be relegated to our range until the propane company starts charging tank rent, then it goes away and in comes an induction range. If we ever do a propane generator, we'll buy a tank at that point.

    Thanks everyone for your thoughts and feedback.
     
  10. gsmith22

    gsmith22 Active Member Forum Leader

    All electric is the future - and probably not too distant a future. It took me a while to get there (old habits die hard and being comfortable with what you know) but the cost of propane really pushed me toward it. we are better for it and I suspect you will be too. Congrats and good luck.
     
    Nicholas Bethard likes this.
  11. Noobie

    Noobie Member

    What we did (although we kept the propane for generator). A leak in our old propane cooktop (so old that parts weren’t available) convinced us to go all electric inside the house. Induction range took a little while to get used to, but is actually very convenient.

    Good on ‘ya.
     
    Nicholas Bethard likes this.

Share This Page