Heat Pump?

[jvlgato]

Considering getting one (Bosch brand) as an upgrade to go with the soon to be installed completely new furnace and AC system.

 

Sounds awesome. Energy savings, save money after several years, current rebate from ComEd, and we have wind sourced electricity.

 

Especially concerned about reliability and durability due to Chicago winters. Also a new model and apparently the first that can be used with any other brand AC/furnace.

 

Anyone have experience?

[Dusty Chalk]

When I was married back in the 90s, we had a house built with a heat pump, and ever since, we jokingly refer to it as a heat suck.  I think the ex-wife has since made things better, but we constantly had to raise the temperature a few degrees higher than we actually wanted it, because when it was always on, the evaporative effect had to fight with the heat pump to keep one comfortable.  But it was the primary source of heat, so hopefully it will work better for you as a supplement.  And hopefully the technology has come a little way since then.

[grawk]

As long as it's a supplementary system to your furnace you shouldn't have any problems. They're only good to a little below freezing. As long as you're not getting a goodman it should be reliable.

[jvlgato]

Thank you both!

This would be a supplement to the main system. And I plan to get a smart thermostat to pair with it. I've heard the technology has improved over the years.

I'm just used to covering my AC compressor over the winter and can't imagine leaving it out there in the elements and even running it through the whole winter.

[Dusty Chalk]

Sounds good.  And yay for saving money and being greener at the same time.

To others considering it as their primary source of heating and cooling:  we were offered the "bury it in the ground" option, don't remember why we didn't do it (I think because the builder didn't want to, he was only offering it to be polite, but he asked while shaking his head subliminally or something), but in hindsight, we really wish we did.  If that's an option, look into it.  The basic concept is, it never gets below freezing once you get below the permafrost layer, which isn't really that thick.  In which case, it can work as a primary system.

[grawk]

In Maryland there isn't a permafrost layer so it's really not thick

[dsavitsk]

Not sure if this applies to your situation, but when we were considering HE boilers versus older ones, we found that the expected life (and the warranty) of the HE unit was about half as long (10 vs 20 years), and was just long enough such that just as it paid for itself, it was likely going to need replacement. Meaning that over time it would cost 2x as much and, in an effort to move from 90% to 95% efficiency, it would result in an extra boiler being dumped in a landfill.

[n_maher]

8 hours ago, grawk said:

As long as it's a supplementary system to your furnace you shouldn't have any problems. They're only good to a little below freezing. As long as you're not getting a goodman it should be reliable.

Not true anymore, Dan, at least with some units.  The Bosch unit that we just had installed in the addition is reasonably efficient down to -15F and provides both heat and AC.

[Dusty Chalk]

3 hours ago, grawk said:

In Maryland there isn't a permafrost layer so it's really not thick

"Permafrost" was not the correct term, but the concept I meant to convey was that below 7 to 12 meters, the temperature stops changing and the ground can act as a heat sink (or cold sink, as it were).

[GrindingThud]

If you are going to have AC, might as well be a heat pump. They are very efficient with some caveats. The BTU output is typically matched to the house size for AC to prevent re-evaporation or short run times. This produces long very long run times in winter to the extent that most home setups reach a balance point around 15-18F where the losses in the house exceed the BTU output and you get 100% run. In Maryland (Where I live) this rarely happens and heat pumps typically keep the house at whatever temp you set the thermostat at without calling for "backup" below the balance point. In the event the heat pump can not keep up (18F for my setup), backup is called. For me, that is electric, which is wicked expensive. In the north, I'd expect the backup system is something other than electric, probably natural gas. Usually when non-electric backup is used, there is an outdoor thermostat that can be set to just swap over the heat pump to the backup (not run both at same time). This is pretty convenient and you can set it at something nice like 25F or so and minimize long run times and maximize your furnace "backup". Heat pumps have an outdoor unit that gets colder than the ambient air in winter (heat) mode. This will cause frost on the outdoor unit. In humid areas (coastal) this frost can be excessive. Most units have a "Defrost Cycle" to get rid of the frost. The way this works is by automatically running the AC (and turning off the outdoor fan) for a few minutes every hour to move heat from the house to the outdoor coils and melt the ice. Some use a sensor to do this rather than a timer. Either way, when it happens, it blows cold air through the house, which many people totally hate. The backup heat is used to minimize the chill, but most people notice it (Dusty Chalks "Heat Suck!"). I'm a heat pump fan, but I'm not sure I would be in Chicago unless I had a good backup.     

47 minutes ago, Dusty Chalk said:

"Permafrost" was not the correct term, but the concept I meant to convey was that below 7 to 12 meters, the temperature stops changing and the ground can act as a heat sink (or cold sink, as it were).

In Maryland, the typical way we do Geothermal is to drill auxiliary wells into the shallow aquifer here. It's cheaper and more efficient than a horizontal trench system. 

Edited April 27, 2017 by GrindingThud

[jvlgato]

I may get the details wrong here, but my guy said there's one control board in the outside unit, one on the inside main, and then the thermostat. The main unit will have the ability to blow air through the house at continuously variable speeds, and will probably run more often than it won't run, but at very low speeds. This will keep the house temp and humidity more evenly controlled. He also explained how the two control boards will work together to figure out which unit should be used - heat pump or gas furnace, as well as fan speed, and this will all work in coordination with the smart thermostat. He explained it much better than I just did, but you get the idea.

It's a $1,000 dollar upgrade, but he said before this particular unit came out, it would usually be a $3,000-4,000 premium for this type of combined unit. Also, there's a $400 rebate from ComEd, so it's a $600 net upgrade cost. Seemed like a good deal to me.

The main concern to me was that he went out of his way to inform me that we'd be his first installation of this particular unit. I thought this was really good and honest of him to tell me, but it did worry me a bit. He said to expect a free service call or two while they learn to fine tune it, but he seriously doubted any major issues, as Bosch is really good, and the coils they chose to use are well known to him to be excellent and heavy duty coils. I didn't understand what 'fine tuning' would entail exactly, but GrindingThud's info likely explains this. And then it just feels weird to run an AC compressor outside in the winter. I get the physics and the heat sink reversal business, but it just feels weird after so many years of shutting it down and covering it in the winter for so many years.

I do appreciate the info everyone, I think I'm going for it.