Replies

1. 
   Peter Yost | Feb 23, 2019 12:12pm | #1

   Hi Frank -

   I am not an HVAC expert but here are two critical concerns nonetheless:

   1. There is no climate for which air tightness is not a leading concern for energy efficiency, indoor air quality, and thermal comfort. You have completed your "envelope upgrade" but don't describe in any detail, including no blower door test results. Both you and your HVAC contractor need to know this part of your envelope upgrade (and so do we in the GBA Q&A community).

   2. I tried to use the detailed specs you provided for each of the system options to identify the Sensible Heat Ratio (SHR) for each of your options and that proved too time-consuming. But you need to know the SHR for each heat pump and ensure that for your climate the SHR is no greater than 0.70, to make sure that you are adequately addressing the latent load (humidity) in your home.

   This is particularly important since none of the three packages includes a whole-house dehumidifier, which frankly would be the best system in my opinion.

   Peter

2. 
   FrankFulton | Feb 24, 2019 09:20am | #2

   Peter,
   Thank you.
   1. We will perform a final blower door before long, and I will post the results.
   2. The Greenspeed claims to have dehumidifier function, but I am also not an expert so cannot interpret whether this is sufficient (or should we require an extra feature).

   Do any other GBAers have insight into the Greenspeed (or other above models) and dehumidification?

3. 
   Jon_R | Feb 24, 2019 11:38am | #3

   Even a SHR < .70 won't keep the house comfortable when there is high humidity and no sensible load. But a dehumidifier can.

   All installers have performed a Manual J, S, T, & D?

4. 
   FrankFulton | Feb 24, 2019 12:25pm | #4

   Jon R,

   We've had manual J load calcs and are comfortable with our phase one approach (replace central unit, with knowledge that if 2nd floor isn't sufficiently warmed then we will add a mini-split in the future).

   We have not had manual S, T, or D. Several of the guys used a ductulator (?) and measured ducts and trunk around the units - all agreed we can move >2100cfm. Frankly it was a serious struggle to find someone who would perform a Manual D, and I eventually decided that given the serious retrofit situation (1950 original custom ducts), replacing the central unit as a first step made the most sense.

   My two questions are about dehumidification (if we go w the Greenspeed) and 10KW as backup heat, which would cover supplemental heat in very cold temps but not a HP failure.

   Thoughts?

5. Expert Member
   Dana Dorsett | Feb 24, 2019 12:34pm | #5

   The 99% heat loads all seem a bit on the high side (particularly the basement, unless there is zero foundation insulation at the walls, which can and probably should be rectified), but the total heat load can be sanity checked against your oil consumption using these methods:

   https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/out-old-new

   Run the load numbers on the "after upgrades" condition of the house, and resist the temptation to oversize "just in case". The turn down ratio of the Greenspeed & similar is only 2.5:1, and duty cycle matters.

   A 5 ton ducted system is probably sub-optimally oversized. Even a 4 tonner might be. Depending on your average wintertime heat load a 3-tonner w/auxiliary heat strips might be the "right" solution. Nate Adams (a retrofit performance home contractor in Ohio) has pretty much settled in on 3-tons at the most optimal size for 90% of the homes he has been dealing with, most of which are in locations with design temps in single (but positive) digits.

   "Normal" sized house with heat loads that would not be covered with 3-4 tons of heat pump usually have enough low hanging fruit worth chasing on the building envelope improvement to make those envelope improvements a better investment in comfort & efficiency that up-sizing the heat pump by a ton (or two). A 3-ton 2-stager is pretty cheap compared to a modulating 5 ton Greenspeed, and spending the difference on fixing the house is usually the "right" place to spend it for best comfort, even at a lower annual return on investment when looking only at net-present-value of future energy savings.

   https://cleantechnica.com/2015/12/10/how-to-really-improve-home-energy-efficiency/

   https://www.greentechmedia.com/articles/read/electrify-everything#gs.aXYoIx5B

   http://www.natethehousewhisperer.com/blog

   https://www.greenbuildingadvisor.com/article/hard-truths-of-home-performance

   https://www.greenbuildingadvisor.com/article/how-an-efficiency-program-killed-my-business

6. 
   FrankFulton | Feb 24, 2019 12:51pm | #6

   Dana, Thank you. I am reading the links now. And I will contact our oil company tomorrow and perform the sanity check that you suggest, and post the results.

   The house is large (3800sqft above grade) , with uninsulated stone and brick walls on the first floor, and uninsulated (but finished) basement walls. I think the load calcs could be accurate. Given the calcs and fact that we are ditching a super-egregiously oversized (168,000 BTUH) oil furnace, seeking 60,000 on the central unit seems reasonable.

   Does any of this additional information change your recommendation regarding a 3 or 4 ton unit?

   Thanks.

7. Expert Member
   Dana Dorsett | Feb 24, 2019 01:54pm | #7

   If the masonry walls are not insulated the load numbers might be real. Insulating those walls would do more for comfort than more heat pump though.

   >"Envelope upgrades nearly complete, so the below heating load calcs will come down slightly."

   What envelope upgrades are currently in process?

   >"The house is large (3800sqft above grade)

   2700' + 800' seems more like 3500' above grade- where does the other 300' come from?

8. 
   FrankFulton | Feb 24, 2019 02:14pm | #8

   Thank you.

   1 Insulating the masonry walls is simply more than we can or want to take on - it would require gutting the house. The good news is that the walls seem to work very well, from a moisture management perspective.

   2. We have air sealed and insulated top attic, crawlspaces (R13 walls and R38 ceiling), kneewalls (along the roofline), and created a few overkill double thermal boundaries, eg above our bedroom we have kneewall roofline and also blew cellulose. We replaced 15 single pane windows with double pane casements and awnings (wooden, to match others in house).

   In terms of current work, we still have one major air leak behind a propane fireplace, which I hope will either be fixed by dense packing exterior wall behind the fireplace, or we will have to remove/seal/reinstall the firebox. After that, the only thing remaining is a poorly insulated flat roof, which we will probably live with for now, then add external insulation when we reroof in 5-10y.

   3. I have two different measures that differ slightly in terms of above grade sqft, which explains the discrepancy.

   Dana, what do you think of the 5ton Greenspeed (or other options above), both for size and performance. You know more about HVAC than nearly anyone on GBA. I appreciate your thoughts.

9. Expert Member
   Dana Dorsett | Feb 24, 2019 02:34pm | #9

   I have no first-hand experience with the Greenspeed, but the specs are pretty good for efficiency and capacity at your 99% outside design temperature.

   Some friends of my spouse went with a 5 ton Trane XV18 on an 18th century antique masonry home that was broken into 3-4 zones. They're generally satisfied with the performance but found the thermostats that came with it unduly complex, and had some difficultly keeping different zones at their desired dramatically different temperatures. (I don't have all the details on that, but it probably doesn't apply to you.)

   Before committing to a system it's important to sanity-check the load calculations against the whole-house fuel-use inferred load numbers. Exact fill-up dates and amounts, or "K-factors", if using a regular fill-up service would be enough. If the propane fireplace was used as a heating appliance regularly, the propane use needs to be factored in as well.

10. 
    FrankFulton | Feb 24, 2019 02:41pm | #10

    Thanks @ Dana.

    Last question: because the 5 ton will be very oversized for cooling (cooling loads 40K BTUH), will the system be able to modulate down and still dehumidify? Or do we need a whole house humidifier?

1. Expert Member
   Dana Dorsett | Feb 24, 2019 02:56pm | #11

   At it's minimum speed a 5 ton Greenspeed is only a 2-tonner, and if set up to run at the minimum blower speed in cooling mode should deliver pretty good humidity control. See if you can download the manuals to figure out what control & setup options the proposed air handler has.

1. 
   FrankFulton | Feb 27, 2019 08:50pm | #13

   OK, working on sanity check for 5-ton vs 4-ton. The salesman was here today for final walkthrough (at my request), and 3 issues came up:
   1. Do we need ducts in the basement? Currently we have no ducts in the basement. 50% of the basement is used as our kid's playroom, and 50% is not used much. To date, the basement has been kept pleasantly warm by radiant heat from the oversized oil furnace. He suggested adding 2x 6" supplies to help relieve potential static pressure in the ducts, and then closing these ducts in the summer. My concerns are comfort for kids and humidity, of course. (Note he also wants me to sign a release about risk of static pressure problems that could require future additional supply ducts being added. None of the other folks saw this as a risk.)
   2. He recommended against the heavy duty filter because it could increase static pressure and does not perform well after the initial period. Is this correct?
   3. Please confirm: If our loads are indeed 60-70k+ (sanity-checked by oil bill), and the 5-ton unit produces 58k BTUH, we should purchase the 5-tonner (w/10KW heat strip) rather than the 4-tonner (w/20+KW heat strip), because the $700 price difference for extra ton will be justified by lower operating costs over time.

   Thank you!

1. Expert Member
   Dana Dorsett | Feb 28, 2019 02:14pm | #15

   If the fuel use numbers indicate a 5 ton or slightly higher load, a 5 tonner it is then, unless you can calculate a one ton or greater reduction in load from your window upgrades (maybe, maybe not.)

   It doesn't hurt to have supply ducts to an uninsulated basement that is used as a play room. The heat pump won't be throwing off nearly as much jacket or duct heat as a high-temp fossil burner does.

   Static pressure issues are equipment & duct system specific, not suitable for a quick analysis via web-forum.

11. 
    user-971368 | Feb 25, 2019 08:21pm | #12

    Why not a ducted heat pump with integral electric coil...Daikin VRVs4 or equivalent. 3-5 ton offerings for outdoor unit, multi position air handler with electric resistance coil. Much better turn down on compressor, 20% or better

    Address the tail wagging the dog first with envelope upgrades - apply an appropriately sized vrv/f

12. 
    walta100 | Feb 28, 2019 02:02pm | #14

    If you trust your manual J then go with its number. If not I feel the smallest unit your installer is comfortable with is still likely to be oversized.

    I think the key features you should shop for are.

    1Two or more speed compressor.
    2 Electronic expansion valves. This device controls the flow of refrigerant one for heating in the outdoor unit and another for cooling in the indoor unit.
    3 Communicating thermostat. This is very important and often overlooked. It allows the indoor unit and outdoor unit to know what the other is doing and work together.

    For dehumidification the smaller the unit is the longer its run time will be. Long run times are what you need to get dehumidification.

    I think if you are happy with the current basement temp then make no changes.

    When you say you are switching to a heat pump as a “comfort upgrade” This statement has me concerned as a heat pump can heat your house but comfortably can be a matter of opinion. My guess is you current oil burner is likely to be blowing 130° air at you and it feels great. You need to understand if you set it at 69° a variable speed heat pump on its lowers speed will be blowing air at 82°. If you duct work points the air directly at you will be very uncomfortable. Please do not get me wrong I like my heat pump but 130° air is a wonderful thing. In my opinion heat pump comfort has a lot to do with your ductwork and your expectations.

    If you want to use the high MERV filter have your installer build a filter rack the will hold 2 filter instead of 1 doubling the surface area and reducing the pressure drop.

    https://www.greenbuildingadvisor.com/article/high-merv-filters-always-reduce-air-flow

    Walta

1. 
   FrankFulton | Feb 28, 2019 02:56pm | #16

   Walta,

   Thank you

   The greenspeed is variable speed compressor and variable speed air handler. At its lowest, it can function as a 2-ton.
   Does this address your concern re run times?

   When I indicated “comfort” in the basement, I was asking if we need ducts to keep it comfortable down there, for kids (since we’ll no longer have oil furnace radiating so much heat). Also, my understanding is that these high end heat pumps blow air at 105 or so, not oil but better than a 2-stage for sure.

1. Expert Member
   Dana Dorsett | Feb 28, 2019 03:23pm | #17

   The Greenspeed is pretty good when right-sized for the load, and it seems you've taken the time to get a good handle on the actual loads.

   Yes, you will need to actively heat the basement with supply ducts to keep it comfortable in winter, not so much in summer.

1. 
   FrankFulton | Feb 28, 2019 05:17pm | #18

   Dana, GBA should add a "buy you a beer (coffee, etc)" feature. Thank you!

13. 
    walta100 | Feb 28, 2019 05:21pm | #19

    Yes you will sometimes see 105° air when it is 5° outside and the unit is running at high speed. But most of the winter it is 40° the unit will be running on lower speeds heating the air about 10-12 degrees over your thermostat setting.

    Another thing to get use to is that it will be running almost continuously if it is 20° outside mine will run 15 or 20 hours Greenspeed likely even more.

    We found it necessary to rise our thermostat set point one degree when moved to the new house with a heat pump.

    Again I am not trying to talk you out of a heat pump but I want you to have realistic expiations.

    Walta

1. 
   FrankFulton | Feb 28, 2019 07:36pm | #20

   Walta,
   Are you suggesting that longer runtimes will produce hotter air? I My understanding was, that the variable speed compressor/variable speed blower units will generate hotter (105*) air during heating, and that these settings (including fan speed) were highly customizable in the system. We've been spending $600 mo for the awesome 130* oil heat, and that is too much. We don't want to drop to 82*, but 105* would be fine. Thanks.

1. Expert Member
   Dana Dorsett | Feb 28, 2019 08:19pm | #21

   Higher modulation levels on the compressor produce hotter air. When the loads are low the compressor is loping along at minimum speed, but the air handler's minimum speed won't necessarily go low enough to keep the exit air temps very high. Another way to put it is, the modulation range on the compressor is greater than the modulation range on the air handler.

1. 
   FrankFulton | Feb 28, 2019 08:38pm | #22

   I'm learning, thank you. Given the turndown ratios of the greenspeed, any guesses whether we can produce hot (105*) air most of the time in CZ4 with a design temp of 17*? Hopefully, with experimentation of the various settings, we can get it right.