AirGenerate AirTap Hybrid Heat Pump Water Heater

[wassermeister]

There is a new water heater manufacturer in the United States that is building cold climate, all in one, heat pump water heaters. AirGenerate has developed a heat pump water heater that can generate hot water with ambient temperature down to 20 degrees Fahrenheit. Most other heat pump water heaters in the US such as the Rheem HP50 and the GE Geospring only work in heat pump mode (the energy efficient mode) with ambient temperatures down to 40 or 45 degrees Fahrenheit. Once it dips into lower temperatures the water heater only operates in electric resistant mode, which is the same as all other conventional electric tank type water heaters. The AirGenerate product seems to be more suitable for Northern climates, since they can generate hot water even in colder winter months.

Does anybody have any experience with the AirGenerate AirTap Hybrid water heaters? I am talking about the all-in one units...the ATI50 or ATI66....

I am wondering what the contractor and home owner perspectives are on this water heaters. Stainless steel seems to be good when the home is on well water.

BUT does it really work? How does it stack up against the GE Geospring, the Rheem HP50, Bosch, or AO Smith unit?

The manufacturer's website is not really that great. I found some information on a smaller website.

What about the price? Is it worthwhile to pay $1,700 for the 50 gallon unit or $2,000 for the 66 gallon tanks?

[Dana]

If the water heater is in conditioned/semi-conditioned space the overall efficiency of a heat pump water heater is pretty much wasted in a heating-dominated climate such as Portland (whether it's Portland ME in US climate zone 6 or in OR climate zone 4.) Putting it in an unconditioned garage or something,even if it's still capable of making hot water at +20F the coefficient of performance (COP) / EF takes a serious dive at those low temps.

The in-situ EF at the average annualized temp of the space where it's located gives you it's electric-heating efficiency, but does not factor in the increased space heating load on the heating system created by pulling heat from conditioned/semi-conditioned space, nor the fuel source & AFUE of the heating system that supports that load. If it's sucking heat out of conditioned space in a house heated with a low efficiency fossil-fired steam heating system you'd be way kinder to the planet and yourself doing something else for hot water. But if it's' in conditioned/semi-conditioned house is heated with a high-efficiency ductless heat pump or ground source heat pump it's likely to be a financial net-win, but whether it's better for the planet than condensing gas-fired system depends on the actual local power-grid sources.

These water heaters are much better suited to cooling dominated or mixed climates like US climate zones 1-3 where there it's more likely to net-win than US climate zones 4-7.

[wassermeister]

Dana,

Your insights make complete sense. My understanding for the AirGenerate AirTap Hybrid is that they are supposed to be adapted to colder climate conditions. I completely agree that they can be difficult in conditioned space with inefficient heating systems.

The climate (at least in the continental US) should only be an issue for up to 3 months of the year when ambient temperatures are low - right? The remainder of the year we should see some savings (depending on gas availability and heating system). In essence we would eliminate or reduce for a few months and save a ton of energy through the rest of the year.

Gas seems to be cheaper if you can get natural gas to the home. Once it gets to rural living propane gas is such an expensive option. I think that electric wins most of the time in such situations unless the home needs a ton of hot water quickly.

Would you agree that a AirGenerate cold climate HPWH is a decent option for electrically heated homes (without access to gas)? Or do you think that a standard electric water heater or Rheem Marathon is better?

[Dana]

Heat pumps only move the energy, and the laws of thermodynamics apply: Any heat pumped into the hot water heater is heat removed from the conditioned space, to be re-supplied by the heating system If the heating system's heat is supplied by using resistive electric heating, the portion of heat pumped into the water from the air is heat obtained at exactly the same efficiency as a resistance heating element in a conventional hot water heater- it's just being moved by the heat pump.

Thus, in an electrically heated home with a conventional electric tank, 3/4 of the year the standby loss of the hot water heater is supporting the heat load at exactly the same heating efficiency as the heating baseboards. A heat pump water would be ADDING to the electric-heated home's heat load, and the savings during 3/4 of the year would be exactly zero.

But during the cooling season the heat pump water heater would lower the cooling load, for a modest savings over those few months. The total annualized net savings on the the combined space & hot water heating would be on the order of 3% at the high end, and the simple payback for the hot water heater would be effectively never- more than 2x the anticipated life cycle of a hot water heater.

For cold-climate electrically heated homes, applying the hot-water heater money toward a ductless air source heat pump (mini-split/multi-split) would be a much better investment, even if the ductless isn't a total solution to the heating. Even in US climate zone 6 a better-class ductless uses only about 40% of the power of resistance heating for the amount of heat delivered (a 60% savings!), and there are many models that still deliver a decent amount of heat even at -5F/-20C (and some with specified output at -13F/-25C). A 2-ton mini-split runs ~$5K installed, and would cut the heating power use of an average sized electrically heated home by more than half, even if the heat load at the design temperature couldn't be met by the mini-split alone. In US climate zone 4 (Portland OR) the heat supplied by the ductless would be more like 30-35% that of electric baseboards (a 65-70% savings). In most cases the simple payback on a ductless in an electric heated home is less than 5 years, and it's often under 3. (Similar or even better economics work in propane-heated homes.)

See: http://neea.org/docs/reports/ductles....pdf?sfvrsn=16

In a house heated electrically with a ductless heat pump or combination of ductless + resistance heat a heat pump water heater would then have a significant efficiency advantage over a conventional HW heater, enough so that it might even pay off before it fails. This is because the BTUs the HW heater takes from the conditioned space during the heating season are being replaced for a fraction of the power used by a resistance element in a conventional hot water heater.

The AirTap Hybrid may still be a net-win over standard electric HW heaters if placed completely outside of conditioned space on a porch or in an unheated garage in those parts of US climate zone 4 where the average annual temp is ~60F, where it works at reasonable efficiency and the 99% outside design temperature for heating systems is above 20F (where it at least still works, where other heat pump water heaters can't.) But every situation is different- there are no simple answers about where they might make sense in cooler climates. The average annual temp in Portland OR is about 57F and the heating design temp is 27F, so there would likely be a net-savings in an electrically heated home if it's out on the porch or in the garage, so long as it is insulated from the conditioned space.

[wassermeister]

Dana,

Makes sense. I would not install a heat pump water heater in conditioned space when the home is heated with electric baseboards. The ductless mini-split upgrade makes sense to get rid of baseboard heaters first.

I read the nwalliance link and they seem to be pushing the Northern climate AirGenerate AirTap product exclusively in electrically heated homes. They allow for the product to get installed in the living space, basement, as well as garages as long as it routes the exhaust air to the exterior. They even got a $1,000 rebate on the product.

Why would they do that if the savings can be neglected in so many electric homes once we install it inside?

[Dana]

I missed the point that the AirTap has the option of taking it's heat from ducted outdoor air rather than from conditioned-space air. (mea culpa!). In the ducted configureation where the AirTap pulls it's heat from the outdoors it would be roughly comparable to installing a competitors heat pump water heater outdoors (slightly better though) and would in fact be more efficient than any competitors unit mounted indoors. With the ducted configuration in conditioned space it takes almost all of it's heat from the outdoors rather than from conditioned space, yet most of it's standby loss it to the conditioned space, and presents no load to the heating system. Key to getting the savings is ducting in outdoor air to the unit. In a configuration that used indoor air it would be pretty much the same as it's competitors.

Getting rid of the baseboards isn't usually advisable when retrofitting ductless, for a couple of reasons: Room to room balance, and absolute heating capacity.

The ductless only puts the heat into the house where it's interior head or heads are mounted. Going with multiple heads is about a $1200-1500 cost adder per additional head. Extremely-well insulated very tight houses can get by with one head per floor, but at conventional R values there will be room-to-room temperature imbalances at the outdoor temperature extremes. The way to manage it for optimal efficiency is to put the ductless head in a larger more open space, and "set and forget" the ductless (no overnight setbacks) to 70F-72F, and set the baseboard thermostat in that room (and others) to 68F (or lower, when unoccupied).

With the main-zone heated via ductless at a few degrees higher than the baseboard-only rooms, a good portion of the heat to the remote rooms will still be coming from the ductless, since the R-values of partition walls and open hallways are very low compared to the exterior walls- there is at least some air-convection moving between zones (the more open the floor plan, the more effective it is).

As outdoor temperatures drop the raw output capacity of air-source heat pumps fall. It's best to size them to be able to have sufficient output handle the load at the 99th percentile outside design temperature or maybe a bit more. But on the freak-day when the temp bottoms out at 0F the ductless doesn't have the capacity to keep up, but with some help from the baseboards to make up the difference you stay comfortable.

Leaving the temperature settings of the ductless alone (rather than setting back overnight or while you are away for several hours) uses less power. This is because maintaining temp has a much lower blower & compressor speed than cranking full blast on a temperature recovery ramp. In these fully-modulating systems the efficiency at the lowest speed can easily be 2x the efficiency at high speed (it depends also on the outdoor temp), and recovering from setbacks eats up any power savings of the lower heat loss of the setback. But if you're leaving for the weekend, by all means bump the temps down.

Retrofitting a one-head mini-split at my mother's place (in Port Orchard WA) resulted in more than 70% reduction in her heating energy use, despite the occasional use of baseboard heat in the bedroom on the coldest days. Hers is one-story with a fairly open floor plan. She still has a ducted hot air resistance electric furnace as the "Hail Mary" backup for extreme events, but has not used it since installing the ductless. It's been keeping up with the recent hot weather just fine in cooling mode too, despite rather low-R value walls and high solar gain windows.

[jadnashua]

I wonder if you ran the duct into the attic and pulled air from there, the dynamics would be better or worse for the house overall...I guess it would depend on how well the attic was vented and sealed from the living space. For much of the year, that air is considerably hotter than the outside air. Maybe run it outside as well, and flip a damper during the winter, if the dynamics were bad.

[wassermeister]

My understanding is that the AirGenerate Airtap is using a Panasonic compressor with fan that pushes 400CFM. There is a $1,000 rebate on this unit for installations in the Pacific Northwest. Qualifying installations must use a so called flow regulator that reduces the airflow to 150-200CFM....the equivalent to 2-3 bathroom fans....

I guess they must have thought about the pressure balance within the home?

The current AirGenerate AirTap Hybrid generations: ATI50 or ATI66 only have an air exhaust duct hook-up. Neither one of them has an air intake duct yet.

The manufacturer seems to have a sealed model with air intake and air exhaust available in Canada. It is not available in the US just yet.

[jadnashua]

Blowing that much air out means sucking in that amount of unconditioned air...doesn't seem too efficient to me! Until you can get one with an external inlet, I'd be leary. If you do have any combustion devices in the house (gas stove, dryer, fireplace, etc.), it could be a danger.

[wassermeister]

You are right. I see weatherization contractors changing out natural draft gas water heaters for Marathon water heaters when they diagnose back drafting of exhaust gases in homes (not a problem for power vented gas water heaters). I would agree that you can run into issues replacing an electric water heater with an AirGenerate AirTap Hybrid water heater....especially if you do have natural gas or propane gas fired appliances. Pulling 400 cubic feet of air from your home may lead to negative air pressure that can prevent the gas appliances from venting properly.

The utilities up in the Pacific Northwest require a carbon monoxide detector and a exhaust air flow regulator that reduces CFMs to 150-200.

[Dana]

If it's exhaust only, it's only more efficient during the heating season than the competition if the air it exhausts is colder than the outdoor air it's pulling in, so it's only going to be a significant advantage in the warmer parts of US climate zone 4 (or warmer.)

[wassermeister]

I just found out that Energy Trust of Oregon is offering a $500 rebate on heat pump water heaters. They are limiting it to the AirGenerate water heater model with exhaust duct. This means that consumers living in Oregon and with electric service by Portland General Electric and Pacific Power (PacifiCorp) can get rebates on heat pump water heaters.

Pretty cool. I guess I have to discuss this with my significant other this week. She will be mad.

[Dana]

I don't know if wassermeister is still paying attention, but I recently stumbled into this relevant resource available in much of OR:

http://www.cleanenergyworksoregon.org/

Before blowing any cash on a highest efficiency water heater, it looks like their free whole house energy assessment is more thorough than any freebies available to me, and they seem to have a "best bang for buck" approach.

[wassermeister]

I don't know if wassermeister is still paying attention, but I recently stumbled into this relevant resource available in much of OR:

http://www.cleanenergyworksoregon.org/

Before blowing any cash on a highest efficiency water heater, it looks like their free whole house energy assessment is more thorough than any freebies available to me, and they seem to have a "best bang for buck" approach.

I am aware of the program. It is good if you need to do an entire energy retrofit. I have a great furnance, insulation, etc.....I am really down to a few little things. I think that the Clean Energy Works program is good for folks that need to get a lot of home upgrades done, don't have any money, and need support. Great program for sure.