Air-to-Water Heat Pumps

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Air-to-Water Heat Pumps

Should residential designers consider using an air-source chiller for space heating and cooling?

Posted on Jan 8 2016 by Martin Holladay

Most air conditioners and heat pumps sold in the U.S. — including most split-system air conditioners and ductless minisplits — are air-to-air heat pumps. During the winter, these appliances extract heat from the outdoor air and deliver warm air to a house through ducts or small fan-coil units. During the summer, these appliances deliver cool air to a house and dump unwanted heat into the outdoor air.

Another type of heat pump, an air-to-water heat pump, produces hot water (or chilled water). When used for air conditioning, an air-to-water heat pump is called a chiller. Almost all air conditioners cool an air stream by blowing air past a copper coil. In a conventional split system air conditioner — called a DX (or “direct expansion”) system — the fluid in the copper coil is a refrigerant. In a chiller-based system, however, the fluid in the copper coil is water (or in some cases, a solution of water and antifreeze).

When used for space heating, an air-to-water heat pump fills the role usually held by a boiler; it requires a hydronic (water-based) distribution system. The heat pump makes hot water; the hot water can be pumped through fin-tube baseboard units, in-floor PEXCross-linked polyethylene. Specialized type of polyethylene plastic that is strengthened by chemical bonds formed in addition to the usual bonds in the polymerization process. PEX is used primarily as tubing for hot- and cold-water distribution and radiant-floor heating. tubing, or a fan-coil unit. (A system with such a fan-coil unit is called a hydro-air system.) The fan-coil unit can be a small wall-mounted unit that looks like the indoor unit of a ductless minisplit system, or it can be a large fan-coil unit connected to a conventional forced-air duct system.

Hydronic systems have pluses and minuses

The main reason that American homes usually use ducts to distribute heat is that most Americans require air conditioning. In climates where air conditioning isn’t required — for example, in northern Europe — space heating systems are usually hydronic rather than duct-based.

Most mechanical engineers love hydronic heating systems, for several reasons. For one, small-diameter water pipes can transfer heat more effectively than small-diameter ducts. (By mass, water has four times the heat capacity of air. By volume, water has a 3500-to-1 advantage over air.) Moreover, water pipes are usually installed to a higher standard than ducts — meaning that unlike ducts, water pipes usually don’t leak. Finally, the circulators used in hydronic distribution systems usually require less energy than the fans used in forced-air distribution systems.

Although hydronic heat distribution systems have a certain elegance, they also have an Achilles’ heel: they are expensive.

The least expensive way to heat and cool a house in North America is usually with a simple forced-air system equipped with a furnace or heat pump. Another low-cost approach is a system using just a few ductless minisplits.

While hydronic systems perform very well, they almost always cost more than either a forced-air system or minisplits.

Ductless minisplits aren’t perfect

While ductless minisplit air-to-air heat pumps are very efficient, they aren’t perfect. Problems with these systems usually have to do with uneven heat distribution (or uneven cooling). These problems arise from the fact that a well-insulated home can usually be heated and cooled with just one or two ductless minisplits. If you need two minisplits, you usually put one in the living room and one in the upstairs hallway; that means that most bedrooms don’t have any space heating or cooling. If bedroom doors stay closed all day, the bedrooms can be cold during the winter or hot during the summer.

In theory, an air-to-water heat pump can solve the distribution problem. With a hydronic distribution system, each bedroom can be equipped with fin-tube baseboard units, panel radiators, or in-floor PEX tubing. That makes sense, except for two problems: (1) as noted before, hydronic distribution systems are expensive, and (2) you still need a solution for air conditioning. (While hydronic cooling systems exist, designers of such systems have to come up with a plan to prevent condensation, puddles, and drips.)

The lower the water temperature, the more efficient the system

Here are a few things to keep in mind if you are considering a hydronic heating system using an air-to-water heat pump:

  • The outdoor unit of an air-to-water heat pump is connected to indoor equipment with tubing that (in most cases) carries water or a solution of water and antifreeze (glycol). In cold climates, the fluid in the tubing can freeze if the percentage of antifreeze is insufficient. Moreover, the tubing connecting the outdoor unit to indoor equipment needs to be very well insulated. Heat lost to the outdoors lowers the unit’s efficiency.
  • Hydronic heating and cooling systems that incorporate an air-to-water heat pump aren’t plug-and-play systems. To design and install such a system, you’ll probably need the help of mechanical engineer, a skilled contractor experienced at designing hydronic systems, or both. For example, most air-to-water heat pumps include a circulator, but the factory-supplied circulator may be inadequate to move water through the system’s hydronic distribution system. The system designer needs to perform flow and head calculations to determine whether the distribution system will require an auxiliary circulator. While contractors who have experience with hydronic systems are familiar with these calculations, such contractors may be hard to find in some regions of the U.S. As GBA reader Dana Dorsett noted, “Read the capacity and temperature [specifications] carefully, there’s still plenty of ways to screw it up. … As with a ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures., the actual as-used efficiency is highly dependent upon the talents of the system designer — it’s not a ‘system in a can’ the way minisplits are.”
  • It’s important to keep the water temperature as low as possible, because most air-to-water heat pumps struggle to make high-temperature water. (The exception is any heat pump that uses carbon dioxide as a refrigerant; in Japan, this type of air-to-water heat pump is called an EcoCute heat pump. The only such heat pump available in North America is manufactured by Sanden.) The lower the water temperature, the greater the heating capacity and efficiency of the air-to-water heat pump. Hydronic expert John Siegenthaler advises installers of air-to-water heat pumps , “Design your distribution system so that it can supply design heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. using a supply water temperature no higher than 120ºF.” Since conventional hydronic systems using fin-tube baseboard units are often designed for a water temperature of between 150ºF and 180ºF, the lower water temperatures produced by an air-to-water heat pump will affect the design of the distribution system.
  • If you’re thinking of designing a hydro-air system, remember that you’ll probably need a special type of air handler — one with more surface area on the copper heat-exchange coil. As Reid Baldwin noted in a comment posted on GBA, “Many air handlers don’t work with chillers, but First Co makes some that do.”

Four air-to-water heat pumps

Because residential air-to-water heat pumps are rarely used for residential systems in North America, few designers and builders are likely to volunteer as guinea pigs for this type of system. For the brave few, however, the first question will probably be: How many air-to-water heat pumps are there to choose from?

If we limit ourselves to energy-efficient residential-sized equipment, four appliances are probably worth considering: the Daikin Altherma, the Sanden, the Chiltrix, and the SpacePak Solstice Extreme.

The Daikin Altherma. While the Daikin Altherma has been distributed in North America for several years, it has struggled to gain much market share — mostly due to its high price. (Installed prices for this type of heating system range from $16,000 to $36,000.)

The Daikin Altherma is an air-to-water heat pump that transfers heat to a water storage tank equipped with a backup electric resistance element. The hot water produced by the Altherma heat pump has a maximum temperature of 131ºF.

The Altherma heat pump can modulate between 20% of rated capacity and 120% of rated capacity. Two versions of the Altherma are available: one version (the split system version) has an outdoor unit that is connected to indoor equipment by tubing that conveys refrigerant (R410a); the other version (the Monobloc version) has an outdoor unit that is connected to indoor equipment by tubing that conveys water (or a solution of water and antifreeze).

One major limitation of the Altherma: the manufacturer does not recommend the use of this heat pump at outdoor temperatures below 5ºF. The rated capacity of a Daikin Altherma unit at 5ºF is about 50% of its capacity at 37ºF.

At least two sources — John Siegenthaler and Rich Williams (the vice president of Alliance Green Builders in Encinitas, California) — report that they’ve heard that Daikin is in the process of withdrawing the Altherma heat pump from the North American market. I contacted Daikin twice and left messages asking the company to comment on this report, but no one at Daikin responded to my call or email.

Sanden. Although the Sanden air-to-water heat pump was developed to produce domestic hot water, the appliance can also be adapted for use as a space heating appliance.

Because the Sanden heat pump uses CO2 as its refrigerant, it can produce hot water at 149°F. The appliance is rated for performance at outdoor temperatures as low as -15°F. The tubing connecting the outdoor unit to the indoor water tank conveys water.

The Sanden heat pump has a couple of disadvantages compared to the other air-to-water heat pumps mentioned in this article:

  • Its capacity is relatively low: only 18,500 BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /h at an outdoor temperature of 30°F.
  • Although it can produce hot water, it isn’t reversible. It can’t produce chilled water.

For more information on the Sanden air-to-water heat pump, see Split-System Heat-Pump Water Heaters.

Chiltrix. The Chiltrix air-to-water heat pump is distributed by HotSpot Energy, a company in Virginia Beach, Virginia. According to John Williams, the CEO of HotSpot Energy, the Chiltrix heat pump is manufactured in Asia.

HotSpot Energy sells several Chiltrix models. The 2-ton model (the CX30) is rated at 30,000 Btu/h for heating and 24,000 Btu/h for cooling.

The tubing connecting the outdoor unit to indoor equipment carries water (or a solution of water and antifreeze). The Chiltrix produces chilled water as well as hot water with a maximum temperature of 131°F. Like most ductless minisplits, the Chiltrix is powered by a DC inverterDevice for converting direct-current (DC) electricity into the alternating-current (AC) form required for most home uses; necessary if home-generated electricity is to be fed into the electric grid through net-metering arrangements. that powers a variable-speed compressor and a variable-speed water pump; these features allow the heat pump to operate at partial capacity — as low as 25% of its rated capacity. Like the Daikin Altherma, the Chiltrix uses R410A as its refrigerant. The equipment is designed to operate at outdoor temperatures as low as -14°F. Of course, the capacity of the equipment drops when the outdoor temperature drops; at -14°F, the capacity is about 50% of rated capacity.

According to the distributor, in heating mode, the rated coefficient of performance (COP) of the Chiltrix when the outdoor temperature is 43°F is 5.97. When the outdoor temperature drops to -14°F, HotSpot Energy claims that the unit’s COP is 2.97. (COP is a measure of efficiency; the higher the COP, the more efficient the equipment.)

Some experts have expressed skepticism at the very high COP numbers reported by HotSpot Energy. When I asked John Williams whether HotSpot Energy could share any COP calculation reports from a third-party laboratory, he said that a report was not available at this time, but that the company hoped to be able to share such a report in the future.

The Chiltrix heat pumps can be connected to in-floor PEX tubing. However, since most people want air conditioning in the summer as well as heating in the winter, it makes more sense to connect the heat pump to indoor fan-coil units. (Appropriate fan-coil units are sold by HotSpot Energy.) The CX30 heat pump can support up to seven indoor units, each rated at 3,500 Btu/h.

Jeffrey Eastman of Athens, Tennessee, is a GBA reader who installed a Chiltrix heat pump. The installed cost of his heating and cooling system was $16,000. He is very satisfied with the system’s performance.

“We had to do some backpedaling to make it work,” Eastman told me. “There really is no skill set for a hydronic system here in the South. The skill set is not as widely available as up north. We’ve learned that you need commercial levels of pipe insulation for the pipes from the outdoor unit that go to the air handlers. That’s been a little frustrating. I was getting insufficient heat. The pipes are outside. When I put my hand on the pipes, I could feel heat loss. I had to put another layer of insulation over it. For longer pipe runs, like one of our runs that goes upstairs, we found out that we needed an auxiliary pump, to make sure that we have full flow up to the second floor.”

In light of the design and installation glitches that Eastman encountered, he has some advice for homeowners interested in a Chiltrix system: “You have to have a mechanical engineer.”

HotSpot Energy posts its prices online. The CX30 heat pump (rated at 30,000 Btu/h for heating) costs $3,400. If that heat pump is paired with two 12,000 Btu/h indoor units, the equipment cost is $4,778.

SpacePak Solstice Extreme. The Solstice Extreme is an air-to-water heat pump that is manufactured in China and distributed by SpacePak of Westfield, Massachusetts. It is rated at 48,000 Btu/h.

The outdoor unit is connected to the indoor equipment with tubing that carries water (or a solution of water and antifreeze).

According to John Baldasaro, the Solstice Extreme product manager, “When producing 130 degree water, it provides full capacity at 0 degrees F. At an outdoor temperature of -10 degrees, producing 130 degree water, it’s capacity is still 45,000 Btu/h. … The maximum water temperature is about 140 degrees. At that temperature, the COP drops off a little bit.”

Baldasaro reports impressive COPs for the Solstice Extreme. “At 33 degrees, with 90 degree water temperature, the COP is 4.5. The COP at 0 degrees F is 2.5, and at -10 degrees, it’s going to have a COP of about 2.3 or 2.2,” Baldasaro told me. “At -20 degrees, you will still get some capacity, maybe 38,000 to 40,000 BTUs per hour.”

As yet, the COP of the Solstice Extreme hasn’t been tested by a third-party laboratory. Baldasardo said, “This unit is going to an ETL [environmental testing laboratory] in California for some testing.”

The Solstice Extreme retails for $7,100. According to Baldasaro, “contractors get a significant discount off of that.”

Siegenthaler advises system designers, “At 0 degrees ambient it can produce 120 degree water at a COP of 2.4, which is pretty good. This unit really needs a buffer tank.”

Is this type of system worth the cost?

I asked Baldasaro what it would cost to install a heating system using the Solstice Extreme in a new 2,000-square-foot house in New England.

“That’s a difficult question,” Baldasaro answered. “The equipment costs might be about $12,000. The installed cost depends on the labor, and that’s a wild card. Installation costs might add $8,000 to the equipment cost, or maybe $12,000. It depends on the contractor. It is going to be more expensive than a ductless minisplit system. It’s not something that we market to everyone. It’s for someone who wants maximum comfort and efficiency. With the minisplit, you can run into humidity control and comfort issues. The Solstice Extreme does a good job of humidity control. It’s easy to zone — you can have a thermostat in every room.”

Good design and installation details are essential

I contacted Kohta Ueno, an engineer at Building Science Corporation, to ask about the advantages and disadvantages of air-to-water heat pumps. “I really prefer DX/refrigerant distribution over chilled water,” Ueno said, “because in BSC’s experience, we’ve seen way too many cases of condensation on chilled water pipes (either on the outside of the jacket, air leakage through the jacket condensing inside it, or poorly insulated fittings condensing), with all sorts of resulting moisture and mold issues.”

Of course, Ueno's concerns can all be addressed with proper system design and installation. The bottom line: if you are considering installing an air-to-water heat pump on a residential project, do your homework.

Martin Holladay’s previous blog: “Green Building in the Cheap Energy Era.”

Click here to follow Martin Holladay on Twitter.

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Image Credits:

  1. HotSpot Energy

Jan 8, 2016 12:53 PM ET

Edited Jan 8, 2016 12:53 PM ET.

Chilled Water Comment
by Kohta Ueno

Great column, Martin! In re my comment--of course, the concerns with chilled water vs. DX (refrigerant in copper pipe) are irrelevant when we're talking about the heating season.

Most mechanical engineers love hydronic heating systems, for several reasons. For one, small-diameter water pipes can transfer heat more effectively than small-diameter ducts (because the heat capacity of water is four times the heat capacity of air). Moreover, water pipes are usually installed to a higher standard than ducts — meaning that unlike ducts, water pipes usually don’t leak. Finally, the circulators used in hydronic distribution systems usually require less energy than the fans used in forced-air distribution systems.

Just to clarify the situation for others in the audience--that's a factor of four mass-based heat capacity. With the density difference, it becomes a huge difference. I'm also citing Siegenthaler here--his Slide 20 in this presentation does a nice job of demonstrating the difference.

Jan 8, 2016 1:28 PM ET

Edited Jan 10, 2016 7:39 AM ET.

Response to Kohta Ueno
by Martin Holladay

Thanks for the link to John Siegenthaler's presentation. I'm reproducing the relevant image below.

I appreciate the suggestion to clarify the mass/volume issue. I have edited that sentence to reflect your suggestion.


Image from Siegenthaler presentation.jpg

Jan 9, 2016 12:29 AM ET

Edited Jan 9, 2016 12:35 AM ET.

Sanden Specs in error.
by albert rooks

Hi Martin,
Happy new year to you!
Where did you get those Sanden specs? There are some errors there:
-The outdoor unit will only return water to the tank at 149F. There is no range of temps.
-Only potable water runs through the outdoor unit. No mixes.
-The outdoor unit is rated to -15F. At this point it is still delivering 149F water. It's just got a low COP of around 1.2.
-The system has a rated capacity of 18.5kbtu/hr

Just FYI: My home is a trial of the COMBI heating +DHW by Washington State University and our regions electric utility: Bonneville Power Administration. There is a lot of good data coming out of that study. Essentially it asks: What else can we do with these DHW installations in low load homes since they do DHW so well, and then sit in idle 18 hours of a 24 hour cycle.

Our company Small Planet Supply will be distributing these systems in late March so it's a topic I'm following closely.

Jan 9, 2016 6:00 AM ET

Edited Jan 9, 2016 6:05 AM ET.

Response to Albert Rooks
by Martin Holladay

Thanks for the information you shared on the Sanden.

I have corrected the article to reflect the BTU/h rating you report, and to reflect that the tubing connecting the outdoor unit of the Sanden air-to-water heat pump with the indoor equipment or tank must not contain any antifreeze. Of course, that limits the climates in which the Sanden can be used, as the danger of freezing increases (especially during power outages).

When I researched the Sanden for my February 2015 article, I found various and contradictory reports on the minimum outdoor temperatures at which the Sanden can operate. In that article, I wrote, "The appliance works at low outside temperatures — variously reported as -4°F or -14°F."

Right now, I'm not sure of the source for my statement that the manufacturer recommends that the unit's operation is limited to outdoor temperatures above -5°F.

One source on cold-weather operation was “Laboratory Assessment of Sanden GAU Heat Pump Water Heater Lab” by Ben Larson of Ecotope, Inc. In that document, Larson wrote, "the manufacturer reports operation to at least -4°F."

An Australian distributor of the Sanden tells purchasers that the appliance is "Fitted with in-built freeze protection, making it suitable for all climates (-10ºC to +43ºC)." The low end of this range (-10ºC) is equivalent to 14°F.

In any case, I was unaware that the unit is rated for performance at -15°F; thanks for that information.

We agree that the unit produces 149°F water.

Jan 9, 2016 8:27 AM ET

refrigerant release
by Charlie Sullivan

Excellent article. Thanks for the research and reporting.

Another advantage of an air to water unit is that it uses less refrigerant than an equivalent split system, and it has fewer places for the refrigerant to leak. That means that on average, there should be less refrigerant released to the atmosphere, a concern because of the high global warming impact of r410a.

In heating dominated climates that also require or benefit from some A/C, I recommend a system using a few fan coil units, supplemented by panel radiators that are used only for heating. That allows setting the fan coil fans very low so they are very quiet, and getting heat distributed as widely and evenly as you like.

For southerners jealous of the hydronic skills in New England, and for northerners expecting an easy installation, note that plumbers used to doing hydronic heat have trouble getting their heads around the level of meticulous insulation needed for a chilled water systems. You may be better off with an installer who is learning fresh.

Jan 9, 2016 11:30 AM ET

by Keith Gustafson

I have no direct knowledge, but in general, nothing that ever goes below 32 degrees can ever have plain water in it.
I would contact the manufacturer for clarification.

The most corrosive thing in a water system is the water, well the water and the oxygen in the water. Antifreeze in your car protects all the metals aluminum brass copper iron steel, from decaying. What material exactly in this unit is so fussy that it cannot tolerate antifreeze, yet so strong that it will last 10+ years without corrosion?

I think there is a misunderstanding somewhere here. Inside the heat pump is a heat exchanger that is either copper or aluminum; a pump that is probably plastic, maybe with a stainless steel impeller, probably one or more solenoids, again plastic and stainless. I would think nothing else would touch the water.

Lots of regular systems have propylene glycol in them after the non return valve

While it is nice not to need an AC guy for the install, wouldn't it make more sense if you are set against anti freeze to run the freon to a heat exchanger inside the building?

Price wise it is in the same ballpark as a high end oil install.

Hydronic is better since it can store heat and it occurs to me with 149 degree water you could create hot water with this system, although with 149 degree water the recovery would be slow. My oil system has a max of 165 and can be run out of hot water if you try.

Jan 10, 2016 12:40 PM ET

Very small typo
by Malcolm Taylor

(By mass, water has four times the heat capacity of air. By volume, water has a 3500-to-1 advantage over water.)

Jan 11, 2016 9:00 AM ET

Response to Malcolm Taylor
by Martin Holladay

Small but important. Thanks for the correction, Malcolm. I appreciate it.

Jan 12, 2016 7:44 AM ET

Nice overview, Martin. We
by Andy McPartland

Nice overview, Martin. We have been looking at this application for some time here in Climate Zone 7, Northern Maine where hydronics rule, and rightly so. Siggy has some great text out there on this (and other hydronic) application.

Some parallel thoughts
- when utilizing radiant cooling be sure to mind the cooling surface temps (ceiling, floor, wall, etc), maintain above space dew point. Consider utilizing a DOAS and/or ERV w/ cooling coil to address latent loads. Simple controls are available to maintain surface skins above dew point and dry.

- Jaga makes a nice LWT panel rad, with a DBE (dynamic boost effect) fan, you can get it with condensate drain - nice units. There are similar offerings from other companies such as Runtal. Smith makes a LWT fin-tube

- Siggy also makes a good point that designing systems around hydronics at appropriate temps has a way of future-proofing your system for what is to come in the future, as can be read more in-depth in his columns

We look forward to more conversations about air to water heat pump applications and how we can best apply them. Keep up the good work. Thanks - andy

Jan 12, 2016 8:53 AM ET

Edited Jan 12, 2016 8:54 AM ET.

Response to Andy McPartland
by Martin Holladay

Thanks for your comments.

I had to look up DOAS -- if any other GBA readers are also scratching their heads, it stands for "dedicated outdoor air system."

You're right, of course, that any hydronic cooling system must either (a) maintain hydronic fluid temperatures that are higher than the dew point of the interior air, or (b) lower the indoor RH to ensure that condensation is impossible, or (c) include distribution methods that collect condensation and direct it to a drain.

In short, designing a hydronic cooling system isn't for beginners. There are lots of ways to mess things up. Thanks again.

Jan 12, 2016 6:42 PM ET

Jaga vs. Chiltrix
by Charlie Sullivan

I bought a Jaga fan coil unit before I learned about Chiltrix. It was the only unit I could find that was capable of handling cooling AND had a low power consumption ECM fan. Chiltrix has the same features in their fan-coils for something like 1/5 the price. The Jaga looks better for sure, but I could have bought some nice handcrafted furniture that looks even better for that price difference.

Good point about future-proofing.

Jan 13, 2016 3:17 PM ET

Edited Jan 13, 2016 3:22 PM ET.

Replacement for oil boilers?
by Ethan T ; Climate Zone 5A ; ~6000HDD

In an old building that already has a copper distribution of hot water from oil boilers, could these be swapped in and run to the existing registers?

Jan 13, 2016 3:26 PM ET

Edited Jan 13, 2016 3:36 PM ET.

Response to Ethan T
by Martin Holladay

The answer to your question is, "perhaps, but probably not."

Most existing hydronic heating systems equipped with a boiler are designed for 180°F water. If you swap the boiler for an air-to-water heat pump that produces 130°F water, the distribution system won't be delivering enough heat to keep the rooms warm on the coldest days of the year.

There are exceptions, however. Some boilers may be hooked up to distribution systems designed for 130°F water, so if you have that kind of boiler, the swap would work.

It's also possible that some hydronic systems weren't well designed -- and ended up with distribution systems that can deliver enough heat when circulating 130°F water to work (more or less by accident). To determine whether you have that type of hydronic system, contact a mechanical engineer. An experienced hydronic installer or engineer should be able to evaluate your distribution system and perform a room-by-room heat loss calculation -- the necessary steps to answering your question.

Manufacturers of fin-tube radiation publish tables that help engineers answer your question. For example, here is a link to a heat output table for a certain brand of fin-tube radiation showing that one foot of their product puts out 560 Btu/h with 180°F water at 1 gpm, but only 310 Btu/h with 140°F water at 1 gpm. The heat output at 180°F is only 55% of the heat output at 140°F -- and most of the air-to-water heat pumps discussed in this article can't even produce 140°F water.

Jan 13, 2016 10:10 PM ET

Air-to-air in California
by Pepper Smith

Great article, Martin. Glad to hear of the activity around the country. We've monitored several Althermas, which used to be approved in CA. Now only the Aermec (the Ferrari of heat pumps) and the SpacePak are approved here. Thanks to the dry climate we find they work great with radiant slab floors (very limited carpeting, no wood or vinyl). A project we did in Tucson using an Aqua Products heat pump showed that radiant floors can be used to store cooling and shift loads completely off peak while improving EER due to cooler nighttime temperatures ( We are also testing a house with two types of ceiling panels and find that even here some form of dehumidification may be needed to keep the panels below dewpoint where rooms need a lot of cooling capacity. We plan to come out of the project with some good design guidelines for ceiling panels.

Dave Springer dba Pepper Smith

Jan 13, 2016 10:18 PM ET

Ways it can work
by Charlie Sullivan


Martin mentions that replacing 180 F water with lower temperature water could be OK if the original design was putting out more heat than it needed to. Another factor that can contribute to that possibility is any envelope upgrades that happened after the original distribution system installation, including air sealing, insulation, or window improvements. Between those two factors, you might be close but not quite able to supply the heat you need, in which case adding a few more radiators or a fan coil can get you there.

As Martin says, figuring that all out is not simple, but it can be done--my house is one example.

Jan 14, 2016 7:46 AM ET

Jaga $
by Andy McPartland

I agree (some) Jaga products are expensive - especially if ordered in piecemeal - we have been down that road - however - it was remarkable the price we got when we did a LWT project with over 10 rads. We went with the tempo, which were cheaper than the typical panel rads available (PNA, Buderus, etc) - the tempo is really just some painted metal panels erected around a nice heat emitting coil, and they can have DBE installed at a later date which makes sense if client decides they want super low water temps but require same btu/h output.

I am not in Jaga's camp by any means. I have been looking at the runtal neo as well but i have not requested any pricing - linked below

I think/hope we will see more offerings on this front in the future

Thanks - andy

Jan 14, 2016 7:58 AM ET

Air to Air CA
by Andy McPartland

Nice application with radiant cooling and peak shifting, and thanks for the report. I would be curious how occupant comfort was with radiant cooling, assuming it would be liken to radiant heating, it has to be more agreeable (comfort, sound, draft, etc) than forced air cooling. Looking forward to hearing about the ceiling panels.

Thanks Again - andy

Jan 14, 2016 1:29 PM ET

Air-to-air in California
by Pepper Smith

We've heard no complaints from the owners of the Chico, CA home. The Tucson builder/homeowner had some discomfort during the monsoon season due to high relative humidity. Lesson learned: when using a chilled water fan coil to dehumidify make sure the system can provide lower water temperatures (~50F) so moisture will condense on the coil. No signs of condensation on the floor at either home.

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