Number crunching

Wow, hard math indeed
Single zone worked for my house because the room layout and machine placement was ideal., for my daughter's house ,a 2 story house, the went with a multizone and it does the job .The last winter was very cold . All of my electric radiant heater were set to OFF , one exception is the bathroom that i kept on. The only time i needed to put the electric heater on was during a blizzard storm at -10F ...the unit was defrosting a lot to keep the evaporator unclogged by the blowing snow. While defrosting no heat is available..it hapenned once last winter ,usually when it snows it is quite mild and the machine performs very well ....

 

For our 2-story house with a single zone central heating by aging oil boiler hydronic baseboard radiators, as described in my comment #101, the biggest problem is heating the downstairs while the 2nd floor is heated by the heat pump. Without changing any of the existing heating systems, the addition of the 15000BTU heat pump on the wall of the central kitchen/dining/family room will heat only that room and two additional rooms on that floor. The downstairs rooms will likely freeze on a very cold night. But to keep the minimal heating downstairs, I would have to keep the thermostat up causing the heat pump upstare not to come on.

As much as I want to get rid of the oil boiler, it seems impractical to completely remove the boiler system and replace it with heat pumps and radiant electric heaters for backups. For one thing, in the case of a power outage which we frequently encounter, there will be no heat without electricity. Our current 7500W portable generator hooked up as a whole-house backup is adequate for running the deep well pump for water, lights and most essential electric appliances (except for oven-grill and clothes dryer), and the central heating system (control unit and fans). If we are to switch to 100% electric heating, I have to upgrade our backup generator to a very substantial size, costing tens of thousands of dollars. Plus we are currently on the 100A main breaker panel. The addition of a single 15000BTU heat pump is OK, but for anything bigger with a multi-zone system, I have a feeling that the main panel has to be upgraded to 200A. I don't have a clue as to what that would cost, but won't be cheap.

It seems the most cost-effective way to upgrade is to replace our boiler with a more efficient modern boiler with an integrated water heater (either oil at max 91% efficiency or propane at max 97% efficiency) and modify it to two zones (upstairs and downstairs), then add a single zone heat pump in the central location in the second floor. Still, it is going to be very expensive. $13K for the boiler, maybe $2K for adding a zone, and $6K for a single zone mini-split, roughly $20K project at a minimum.

 

OH yes i can understand the multiple chalenges you are facing .
Just to add info on my daughter's 2- story house , the multizone has one 12000btu on each floor and with their experience they say that in winter the unit on the first floor works harder than the unit on the second floor ....and in the summer when cooling it's the opposite.
Originally the house was centrally heated by a forced air oil furnace . They replaced the oil by and electric furnace . This systeme is a back up if the heatpump fails in winter...... they have a 200A main panel like i have also.
no backup generator in either house to feed the heating system ....cost would be to high .Major Power outages does not occur frequently ...maybe once in 20 years.

 

Thanks. That is at least one number I can compare to when I get a new quote for a muti-zone system. I don't have any good reference points to compare, so I don't know if that is good or bad. Certainly, if that price applies to my application, meaning being able to heat 3 zones in our home with a single 36,000BTU multi-zone heat pump that would be much cheaper than installing two single-zone 15,000BTU heat pumps at $6000 each.

 

I have a propane fired fireplace in what is my large upper level. 4 D-cell battery start in a pinch. Cost to fill tank is significant. In the winter, to keep it tested, I run it for maybe a half hour in the morning to take the chill off and ease the load on a heat pump that turns to resistance heating if it gets too cold out. A tank lasts maybe two-three years using it that way.

I suspect running it if the power was out would at least keep the pipes from freezing.

 

Do you use thermostat setbacks at night, turning the temperature back up in the morning? If so, have you tried NOT setting back, to see if the heat pump can hold up overnight and not need supplemental heat (resistance or propane) in the morning? With a heat pump, the less efficient backup or supplemental heat can very easily outweigh the setback savings.

I've heard stories of some HVAC outfits telling their residential customers to not use setbacks because it takes more energy to rewarm a house than the setback saves. But this should never be true with common combustion and electric resistance heat, absent some unusual non-linearity in the heating system.

Heat pumps do have such non-linearities, so could very easily fall into this trap. But there are enough variables to preclude a simple or general answer, other than doing your best to avoid the backup heat. Careful analysis, beyond the resources of most homeowners, is needed to get a better answer.

Because my first heat pump is not central, just a single zone ductless unit in the largest area and trying to get some heat to flow to the far end of the house and displace some of the electric resistance there, I quit using overnight setbacks almost immediately after installing it. This also made the house more comfortable, as there is no morning chill that takes a long time to recover. Heat pumps, being lower power than most other heat systems, take longer to recover.

We do still use setbacks for multi-day absences.

 

Yes you are right , things happens slowly with a ductless heatpump and setting back is conterproductive. If I may add , turning them off in winter is not a good idea, most of them after 30 minutes of inactivity will consume electricity to keep the rotary compressor warm.

 

Here is a study on home temperature setback to determine if it is myth or fact.

Myth Buster: Using a thermostat setback for energy savings - Powerley

If You Think Thermostat Setbacks Don't Save Energy, You're Wrong! - Energy Vanguard

May thermostats have provisions to control the rate of temperature recovery to prevent emergency heat from coming on or/and provisions to temporary 'lock out' emergency heat in certain situations.

Example you setback your temperature 5 degrees at night. In the morning the thermostat anticipated you want your temperature 5 degrees warmer and will begin heating up your home to this temperature at a rate of 1 degree per hour or whatever rate you set it at to insure your home is at the proper temperature when you wake in the morning.

One of the overlooked aspects of temperature setback is it decreases the amount of temperature loss in the home at your lower temperature setpoint. Your heat pump will still need to run it just won't run as much or work as hard during the setback period.

A good point was made in that it is imperative your emergency heat remain inactive in the recovery period or your savings may evaporate when the home is bought back to temperature

 

I also have heard/read that the constant thermostat setting saves more. I am a bit skeptical of such a claim. I don't know how the temperature setback affects the HP operation in a cold climate especially if it is linked to some type of emergency heat source such as a resistance-based electric heater. As pointed out by @John321, I can imagine that if the setback triggers a low-efficiency emergency heat source more often, then it is understandable that the practice will not save any energy or money.

But for our single-source oil boiler-based central heating, the setback does save fuel and money as we lower the thermostat temperature setting. However, we do our setbacks quite opposite of what most people do. We set the thermostat's temperature lower during the day. During the day, we are more active, and putting on more layers if chilly is no big deal. Plus, during the day, we get solar gain from windows that heats our house. During our typical winter day, we set the thermostat at around 56-58F. During the nighttime, we tend to notch up a bit to 60 to 62F.

 

Here is an example of a thermostat that can be used - the mode is called smart recovery that must be accessed

What is Smart Recovery and how does it work? (ecobee.com)

"Note: Smart Recovery is a learning algorithm and can take a couple of weeks to fully determine how far in advance to turn on your equipment. You may notice that the thermostat is engaging earlier than it should however it will be continually learning your HVAC equipment's efficiency and become more accurate with use."

Many of these thermostats are now programable and have blue tooth access. They are microcomputers and can control your system and its components to work however you desire within safe limits. You can program and control the heating and cooling system throughout the day for each day of the week and tailor the heating/cooling system to your lifestyle and the thermostat will automatically find the most efficient cost-effective way to have the system perform to meet your families comfort goals.

Some thermostats allow this programming access to owners and other thermostats require an unlocking code so only qualified personal can access their advanced settings

 

we have the same problem with radiant heat. you can't set it back much, or it takes forever to rewarm the floors, furniture, etc.

 

Here you can see data from the manufacturer for my Cold weather heatpump , For easy interpretation I circled the data.
IP= Input power in Kilowatts
the example shows that for a given outdor temp i.e -5 F reducing the inside temp setting from 70 to 65 F reduces the input power from 2.24KW to 2.20 KW ......40watts saving for chilling the house it looks counterproductive to me

 

A couple seasons ago, I bought a bed warmer thingy. It has a pad with tubing, and a separate unit that heats and pumps water through.

Its marketing kind of aims at people who are worried about EMF from electric blankets, which isn't really me, but I was aware of some possible electric blanket hot-spot failure modes that could be burn or ignition risks. and the water tube thingy is free of those too.

It allows programming of both the water temperature and the time of operation. After some experimenting, I landed on 42 ℃ and a two-hour run time, which ideally I start a half hour or so before I turn in.

In those two hours, it imparts enough heat to the mattress, bedding, and me to keep me toasty the rest of the night, and uses about 1/4 of a kWh*, while meanwhile I've made my nighttime thermostat setback a full ℃ deeper than it was before.

Their newer version of the product includes a TE cooler, so it can circulate cool water in summer, as well as warm in the winter. I don't have that one.

* edit: I wrote 3/4 first, but it's 400 watts, so 3/4 kWh is about what it would use in two hours running flat out. Set for 42 ℃, it cycles, and when I was running on my Kill-A-Watt, more like 1/4 kWh per night is what I'm remembering as I think about it more.

 

Notice that neither of these articles is specific to heat pumps. The first doesn't mention heat pumps at all, its discussion portion mentions only natural gas.

The second mention heat pumps only in passing, after the Conclusion. Its analogy, "your HVAC system is like a faucet and your building envelope like a cup," and the accompanying math, properly describe only fixed-efficiency heating plants such as electric resistance and most combustion (natural gas, oil, etc.) systems. Heat pumps have variable efficiency, depending on temperatures. In addition, ductless minisplits are nearly always variable speed inverter driven systems, not a constant single speed as the old-era heat pumps were. Their efficiency varies with load too, being more efficient at low and rated loads than at maximum loads. So the differential equations are different, and these articles don't address that at all.

For fixed-efficiency heat systems, your skepticism is very well placed. The differential equation solutions pretty much prove that the "constant thermostat setting saves more" claims, violate basic physics.

But variable-speed, variable-efficiency heat pumps are different. Heat output from the pump is not an accurate proxy for electric energy input. Even in normal DHP operation, without other back-up sources, high load make-up heat while catching up in the morning is less efficient than constant lower-load heat. The trade-off is -- undetermined without considerably more information, some of which is specific to a particular building and installation and to the weather de jour.


I should also note that the better the building envelope, the longer it takes to cool enough for there to be any meaningful savings from setbacks. E.g. dad's really old house (when I was growing up, before a couple significant improvements) would get noticeably cold in about 15 minutes after the power went out, even with some wood furnace heat still leaking upwards. My much newer house, with numerous building envelope improvements, doesn't get similarly chilled for 4-8 hours. During a spate of power outages last winter, I didn't even think about firing up the old wood stove until the outages dragged beyond 6 hours.

 

Kind of like Don Quixote tilting at windmills and fighting dragons that aren't really there.

Heating setbacks are a great energy saver for those who want to use them. There is no argument. I won't fight, or get into a contest, you'll need to find someone else. The information is for people who may find a use for it and are interested in ways to optimize systems and save energy

Programmable thermostat myths: Know the facts and boost your profits | ACHR News

"Now for the heat pump part of the myth. The fact is, programmable thermostats do work on heat pumps.

True, the first programmable thermostats didn’t have advanced features like Adaptive Intelligent Recovery and would sometimes bring on auxiliary heat to recover from setback, thereby reducing energy savings. But they still saved energy. And today’s “intelligent” programmable thermostats provide excellent performance.

The best new programmable thermostats minimize the use of costly secondary heat, which is typically electric heat. According to the EPA, energy savings garnered by Energy Star-listed programmable thermostats and heat pumps are impressive.

As for that recurring myth that the energy savings you get during setback (or setup) are lost during recovery: It just isn’t so."

ChapmanF suggestion is a simply wonderful way for a homeowner to feel comfortable through the night and not even know they are in setback mode. They even make these sleep blankets in dual zones where couples can sleep in their own comfortable setting.

 

Not one peep about heat pumps there.

Unfortunately, that article is written too much in the form of marketing fluff, focused mostly on seller profits.

Also unfortunately, that article has no supporting links for references, so I had to go looking for them myself. Here is what I found (emphasis added):

Energystar.gov: ENERGY STAR Most Efficient 2022— Central Air Conditioners and Air Source Heat Pumps

"The ENERGY STAR Most Efficient 2022 designation recognizes the most efficient products among those that are ENERGY STAR certified. These exceptional central air conditioners and air source heat pumps represent the leading edge in energy efficient products this year. These systems are designed to provide the best comfort for the least energy with the associated thermostat, controller, or application identified below. For most of them, an ENERGY STAR certified thermostat may not be the best option for control. ..."


Energystar.gov: Energy Efficiency Program Sponsor Frequently Asked Questions About ENERGY STAR Smart Thermostats

"Are there certain customer types or home/equipment characteristics that are likely to yield greater or lesser energy savings?

Yes, homes that experience extreme changes in temperature over the course of a year will generally see greater savings with ENERGY STAR-certified smart thermostats. Temperate climates usually spend less on HVAC bills and thus, savings are generally slightly lower. Regardless of climate, homes that are always occupied will see less savings. In addition, homes with variable capacity (as opposed to single-speed) heat pumps or air conditioning will generally perform best with a manufacturer-recommended thermostat regardless of whether it is ENERGY STAR certified."

I never claimed that programmable thermostats can't work with heat pumps, only that this is a more complicated issue and in some cases may not work as expected. With modern variable-speed heat pump equipment, the answer isn't nearly as clear cut as it is with other forms of heating plants.

 

I have never used a heat pump to heat our house, so I don't have any first-hand experiences or data to share. But I found this piece of article. It is an "ask an expert" type of newspaper column on energy saving. It kinda makes sense to me. In a nutshell, a setback on the heat pump can end up costing more energy, but that is only because it may use the backup resistance heater to shorten the recovery time.

Setback System On Heat Pump Might Actually Be Energy Waster

Two questions came to my mind.

1. Are all heat pumps have built-in electric resistance ``secondary (auxiliary or backup) heat'' system?
   
2. How is the special heat-pump setback thermostats mentioned in the article differ from other "smart" thermostats?

Now, what I think is that if a heat pump does not have a built-in electric resistance heater, plus no other secondary backup heater would be turned on in the room where the heat pump is located, and the operator is fine with slow recovery time and some discomfort in the cold morning after the setback. Wouldn't it make sense that a lower thermostat setting during the day (or night) would certainly save energy compared to keeping the thermostat at the high point all day long even in a house solely heated by a heat pump? For example, setting the thermostat at 68F all day long vs setting it back to 62F for 8 hours during the night then bringing it up again to 68F in the morning. I understand that the energy saved may not be a lot, but still, less energy will be used overall, isn't it?

 

My variable capacity gas furnace can be configured to work with a manufacturer-proprietary stat or a conventional one. The proprietary one communicates with the furnace using the four basic stat wires as a serial comm link, and it can tell the furnace things like "temp is this far from setpoint" and the furnace can directly choose an appropriate firing rate.

When operated by a conventional stat that only says "heat please", the furnace has its own heuristic where it starts at a firing rate similar to the last cycle, and increases it gradually if the call for heat lasts longer than expected, or decreases it some if the call doesn't last as long as expected.

I considered the proprietary stat, but it was $400, and then I would have locked in the brand of the furnace (or required another change of stat down the road). So I got a fairly smart, but conventional, Honeywell instead.

Clearly, the operation with the proprietary one would be more optimal, but things work out pretty well with the conventional one. It's interesting that the furnace and the stat both seem to have learning algorithms in play, and they play reasonably well together, and converge on some sensible behavior, rather than continually surprising each other.

If I had the multi-stage A/C or heat pump that matched the furnace (I don't), the proprietary stat could also control that directly. But the conventional Honeywell is at least able to ask for two stages of cooling and to be configured for a heat pump, though I'm not using either feature at present.

 

no built in electric resistance in cold climate inverter driven heatpump please look at post 133 before contemplating smart thermostat