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Creative, efficient and low-cost radiant cooling system?

unclejemima | Posted in Mechanicals on

I’ve probably asked this before and I apologize if this is a repost…but I’m looking to rig some infloor cooling to my house.

Living in Northern Canada we don’t get many “hot” days, but for 3 weeks of the year it would be nice to reduce the temp by a few degree’s.

The house is 100% radiant heat with a Viessmann boiler and indirect Viessmann Stainless Steel Domestic Hot Water system.

The house has HRV’s as its only way of moving air. I have them set to run at low speed every 15 minutes in the winter (as the air is already dry, and with it running constant it gets REALLY dry as the HRV seems to dehumidifies the air)

In the summer its tempting to run the HRV on Med or High speed all the time but this just increase the house temp when its hot out.

I’d like to rig the infloor cooling only to lower the temp by a few degree’s. Not looking for chilled air at 68F as everyone seems to run. 72-75F would be fine. Summer outside temps when its hot are usually about 85 max for 3 weeks in where we want to cool the house ever so slightly.

I’ve rigged the HRV with radiators that are fed by the infloor heat system to slightly warm the air in winter. What mean in the summer if I can also cool the water, it will also cool the air.

I’m obviously more concerned about cooling the water for the floow. I’m aware the high dew point but I should be able to bring the water to about 59-60F without any issue of condensation?

So…how to cool the water. That’s the question.

I was hoping to get some sort of device I could mount beside the Boiler that would cool the water instead of heating it. Something gas fired preferably, or electric. Something that is not to expensive.

I even though of getting a old fridge or freezer, putting a roll pex inside and drilling an inlet and outlet for the PEX and just let the fridge or freezer run and as the water entered and circled through as much PEX as I could cram in there would cool and continue on its way to cool the house.

Looking forward to any crazy idea’s 🙂

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  1. GBA Editor
    Martin Holladay | | #1

    The device you are looking for is called an air-to-water heat pump (or a chiller). Here is a link to an article about these devices: Air-to-Water Heat Pumps.

    Your biggest risk is condensation on the floor. It can get slippery -- be careful.

    -- Martin Holladay

  2. Expert Member
    Dana Dorsett | | #2

    It has to be a heluva big & oversized HRV to increase the indoor temperature significantly in summer, even higher speeds!

    The only way to know if 60F water is going to be a condensation issue is to track the indoor & outdoor air's dew point levels. Being a bit more specific about your location would be useful. "Northern Canada" can be interpreted many ways, and in any interpretation covers a enormous amount of area, with quite a large range of summertime weather. If there's a reliable weather station within 100km of your location it may be possible to simply look up the outdoor dew point data, but also the ground water temperature data.

    There are plenty of air-source chillers out there that can deliver 60F or cooler water at high efficiency, but it won't be cheaper. You may need cooler water than that to deliver the amount of cooling you actually need. Water to water heat pump solutions can work too, if you have a well to draw from, but also more expensive than more conventional approaches to cooling.

    A hacked refrigerator won't work, since it dumps the heat it's taking out of the water back into the house that you're trying to cool. The condenser coils have to be outside the thermal envelope of your house for it to work.

  3. GBA Editor
    Martin Holladay | | #3

    To be clear, I think your project is a little nutty -- it's going to cost a lot more more to set up than just buying a window-mounted air conditioner.

    If you want to invest the big bucks, you can invest in a buried glycol ground loop. Here's a link to more information: Using a Glycol Ground Loop to Condition Ventilation Air.

    -- Martin Holladay

  4. charlie_sullivan | | #4

    I don't know how humid it is in your location, but if it's humid during those hot summer days, I would suggest cooling the incoming ventilation air down lower than 60 F and deliberately condensing some of the moisture out. Then you probably don't need to cool the floors at all. You won't get much cooling that way, but the comfort benefit from the dehumidification might be most of what you need; add a little additional cooling and you are all set.

    If you give us a postal code or location we could look at humidity data and see more about what makes sense.

  5. Expert Member
    Dana Dorsett | | #5

    C'mon, guys, up in the wilds of Northern Canada you need to have SOMETHING for a hobby to keep you from going crazy! :-)

    Distributing coolth with the HRV system doesn't make any sense, at all but chilled hydronic loops using the heating radiation (in this case radiant floors & or ceilings) may still have merit for the truly dedicated, even in modest-load short cooling season locations. But there's a design process for figuring out the necessary water temperatures, as well as the controls to avoid condensation on (or excessive moisture adsorption into) the floors. Radiant cooling is something of a luxury item, but works fine in reasonably dry locations.l

  6. Reid Baldwin | | #6

    Replacing the HRV with a Minotair might be worth adding to the list of options. I am not saying it would win. It would be considerably more expensive than a window air conditioner, but might be competitive with a chiller.

  7. unclejemima | | #7

    Hi everyone. Thanks for the fantastic replies. Postal code T8V0Z7 for those who are able to check moisture levels. Our summer are fairly dry.

    As the only way I could cool the air is with the HRV (what sounds like its not very practical) the only way I could cool my house now is with the floor system.

    Again, really looking to reduce the temp slightly.

    Thanks for all the kind advice!

  8. user-2890856 | | #8

    You will have to monitor dewpoint . You should keep the water at least 3 degrees above dewpoint to avoid condensation . In low dewpoint periods colder water is easily used . Check out Massana website . They may even sell the control system that monitors dp and mixes the water to proper temps based on that reading .

    Dana , What is coolth ?

  9. GBA Editor
    Martin Holladay | | #9

    Coolth is what humans experience as heat leaves their bodies...

    When a poorly dressed human goes outdoors in January, he or she might exclaim, "Wow! Feel that coolth!"

  10. SwitchgrassFarmer | | #10

    Martin, based on your definition, I guess it's good to be "uncoolth" then.

    Here is an interesting discussion of the word "coolth":

  11. Expert Member
    Dana Dorsett | | #11

    Coolth is merely the opposite of warmth. It's been in the English lexicon since the mid 16th century but only became common in the 20th century, according to the OED:

  12. lance_p | | #12

    I was thinking along the lines of what Martin said about a ground loop. Your deep soil temperatures are likely cool enough to allow a cooling coil to be added to your HRV supply while condensing out some moisture.

    In reference to some suggestions above, can someone clarify why conditioning the HRV supply air would be ineffective at cooling a home? It would seem to me that even 50 CFM of cool dry air into a home would have an impact, especially if the outdoor temps only ever got to 85F and the solar load wasn't crazy. ?

    Going one step farther, running the supply side of the HRV only (shutting off and blocking the exhaust side, if possible) would positively pressurize the house and keep hot humid infiltration air to a minimum during the cooling season, which could increase effectiveness.

    My brother is in Edmonton and I get the impression it's a reasonably dry climate out there, so humidity control may not be too much of an issue. If you know your dewpoints cooling the floor might get you some relief, or at least keep your feet cool. Be careful, 85F air at only 60% RH will condense around 70F, so without a method of controlling your indoor humidity levels your floor cooling potential will be very limited.

    Here's a link to a handy dewpoint calculator. It's intended for artwork preservation but the data is the same regardless. If you monitor your indoor temperature and humidity levels you can get an idea of how cool your floor could be kept before condensation would be an issue.

    As others have suggested, a small window mount air conditioner could be the most practical and cost effective solution, especially if your house isn't too large. If it is a bigger home, buy two! The only pain is installing and removing them seasonally. Also, not the best looking of solutions, but it probably beats having an old refrigerator in your yard with PEX running to and fro.

  13. Jon_Lawrence | | #13

    I know Zehnder makes a ground loop heat exchanger that can be added as a front-end to its ERV to provide additional cooling and dehumidification in the summer and heating in the winter. I recall someone telling me it could provide up to 1/2 ton of cooling in the summer. The attached document provides the cooling and heating capacity charts which I am not sure how to read.

  14. GBA Editor
    Martin Holladay | | #14

    Reality check: a Zehnder ground loop will cost between $2,000 and $3,000 to install, and will never provide enough cooling to compare to the performance of a $300 window-mounted air conditioner.

    Just saying.

    -- Martin Holladay

  15. Expert Member
    Michael Maines | | #15

    People seem to think that as long as your surfaces are below the dewpoint temperature you are safe. In fact, the greatest risk of mold growth is when the relative humidity near the surface is in the 80% range. The actual formulas in ASHRAE Standard 160 ("Criteria for Moisture Control Design Analysis in Buildings") are somewhat complicated, so as a rule of thumb it's safer to keep RH near cool surfaces below 70%.

    In a room with air at 70°F and 50% RH, surfaces should stay above 60°F to keep the RH below 70%. 85°F air would have to be below 30% RH to avoid risk of mold growth on surfaces at 60°F.

  16. Jon_Lawrence | | #16


    In Mark's situation, no doubt about that. However, I wonder how cost-effective it is where I live in a new build project. I can run the ground loop around the footings during construction, but it will still cost me $2-$3k between the PEX, ComfoFond unit and install. I will get year round use of it as opposed to the 3 weeks in the summer that Mark is looking to cool. I know Matt Bowers installed it in his RESNET prize winning home. I will try to reach out to him and see what his experience has been.

  17. GBA Editor
    Martin Holladay | | #17

    There is a lot of discussion of the situation you are contemplating in the article I linked to, and in the comments posted on that page. Here is the link again: Using a Glycol Ground Loop to Condition Ventilation Air.

    -- Martin Holladay

  18. Jon_Lawrence | | #18


    As usual you have an article for everything - thanks.

  19. charlie_sullivan | | #19

    A look at the weather data at:
    shows a few interesting things. One is that the average temperature over the year is below 40 F, which means that the deep ground temperature will around that temperature low, and the cooling you can get from a ground loop system would give you excellent performance, including the ability to do excellent dehumidification if you run it through a water to air heat exchanger on your incoming air, whether that's the expensive Zehnder system or a homebrew system.

    But the dew point is never very high--typical daytime highs of 54 F in the peak of summer, and almost never higher than 60 F, with night-time lows about 10 F lower. That means that dehumidification is not essential, and it also means that night-flush cooling could work very well without causing humidity problems. That could be done with a window fan, perhaps on a timer. An HRV with bypass capability could also do some of that job. A whole house fan into the attic is a typical solution but I don't think that makes sense in this case as it's hard to do that without some heat and air leakage in the winter.

  20. Jon_R | | #20

    While a HRV duct isn't good at moving significant BTUs, it is useful for dehumidification and can be combined with radiant cooling. Look up "DOAS" for more information.

    You are correct that positive building pressurization controls where humidity enters, making it easier to address.

  21. Expert Member
    Dana Dorsett | | #21

    Grand Prairie? That's not Northern Canada, it's not even as far up as Fort MacMurray, let alone Whitehorse or Yellowknife! But OK, it's not the Hamilton to Toronto "Ontario Riviera" either... :-)

    The mid-summer dew point averages in Grand Prairie look favorable for radiant cooling. Take a peek at the dew point averages graph near the bottom of the page Charlie pointed to:

    The 90th percentile outdoor dew point just nudges on 60F, so with insulated plumbing and reasonable ventilation rates (so that the indoor dew point tracks reasonably closely to the outdoor dew point) you can use 60F water without much risk of dripping or puddles.

    But as Charlie also points out, the temperature graph on that page shows that the 90th percentile overnight low temp is below 60F, which means a nighttime ventilation strategy using a thermostatically controlled whole-house fan can also work well. I'd hazard that outdoor temps north of 75F at bed time in that location are pretty rare, but the evening solar gain near the summer solstice can still be pretty high as late as 9PM if you have a lot of west facing window.

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