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Existing ground source heating system upgrade to cooling complications

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hausfxr
hausfxr Member Posts: 4

We are at the planning stage of having cooling added to our house which currently is heat only from a water-to-water ground source heat pump and in-floor hydronics. We’ve been renovating the house in stages for over a decade, and only recently decided we need cooling – Portland, Oregon, which, until recently, had very mild summers.

My questions are about our existing system and how it will be modified to accommodate cooling. Unfortunately, we have a very small utility room, so I’m trying to get a handle on what components will be added or taken away and the attached diagrams show our existing and my guess at what might be needed. I’ve looked at system diagrams and descriptions online and most of those are much more complicated than what we have or what I have anticipated would be needed for the cooling upgrade, but those that are complicated probably perform better – some of the most complex looking systems I’ve seen are by John Siegenthaler, P.E., and, as we found out when the heating system was installed, there is a great variety of options/opinions on what’s considered optimal. For our original heating only system, we chose to go with the simplest system in the end that our contractor, a mechanical engineer, recommended.

Can we eliminate the heat exchanger?

Does an additional DHW tank need to be an indirect type like the one we have now?

Any other recommendation or links to a good system diagram/description would be appreciated.

The rest of this post is only indirectly relevant to my query, and just a little more background on our project to explain why we have not contacted the original contractor:

We installed the in-floor pex heating loops as our renovation progressed (tore down our old plaster ceilings then insulated the cavities) ourselves, and, as we replaced our foundation, we ran the ground loops – all done as recommended by the HVAC contractor. However, after the contractor scheduled the installation of the equipment side of the equation, he was many weeks delayed, and, with the 30% tax credit near to expiring and no Congressional renewal, he announced that Water Furnace had raised the heat pump price by $4k due to federal government requirements, and their $14k estimate was now $18k. Then, when we hesitated, he reminded us about the tax incentive expiration and added that he did not need the work. He ended up arriving on the 4th of January, four days after the incentive expired, and reassured us he would back-date the invoices. When they were done with their installation, they had not hooked up the new hot water heater they provided to the domestic water or run electricity to it, saying we would have to hire our own plumber and electrician because that’s not allowed by their licensing.

I could go on with a few more things that were sketchy, but you probably get the picture. Had they charged me $18k for the job to begin with, I would gladly have agreed – I had no idea what the install should cost, and I just wanted professional workmanship and consideration.

The week after they finished their work, Congress extended the tax credit.

I’ve worked in construction all my life, and I’ve seen much, much worse than this, so you learn to take these things in stride. The system has worked flawlessly, even in the weeks when temperatures have reached the low twenties at night (yes, winters are mild here), so we are pleased overall.

For this next stage, I want to be a little more educated before we decide on a system – we’ve already met with a contractor about a DX system before someone pointed out in a subsequent forum discussion that our existing Water Furnace heat pump is reversible – it even has unused ports stating DHW in and out. We contacted the contractor with this news, and he tried to talk us out of the chilled water system – though he never said it directly, we assume this is outside his area of expertise. We realize water chilled systems in residential are not the norm, so we may need to advocate for that system with anyone we talk with further.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    It sounds like such a wonderful idea…

    There is a fundamental problem with chilled water direct cooling — such as a retrofit to a floor or radiators or something of the sort. Condensation. Just for example, as I type this in New England, the outdoor air temperature is 90 F, and the relative humidity is 90%. Sticky, but bearable. However, the dewpoint is about 84 F, which means that any surface cooled below that temperature will condense moisture. Lots of moisture. In fact, it will be soaking wet. And worse, the air temperature next to the surface will not drop significantly below the dewpoint.

    You mention you are in Portland. Now if you had said Redmond, or John Day, you might have had a chance with direct cooled surfaces. Portland? I very much doubt it.

    So… how does air conditioning work in a place like Portland? Quite simply the air is cooled well below the dewpoint, and the condensation is piped — or dripped! — away somewhere, and the cooled (and now dry) air is blown into the space. This does work splendidly well, and can easily work with a ground source, water to water heat pump — provided you have the chilled water run through coils which cool the air, and a duct or some other means of blowing that now cooled air into the space.

    So… you are going to need some air handlers and ducting…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,483
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    chilled water in the radiant loops and an air handler?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    That would do, @Steamhead — run the chilled water through the air handlers first, to do the dehumidification and heavy lifting, and then the return through the radiant loops in the floors — just making sure that the floors never dropped below the dewpoint.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 17,008
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    All Steamed Up, Inc.
    Towson, MD, USA
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  • DCContrarian
    DCContrarian Member Posts: 305
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    You're basically going to need a separate system. As others have noted, your floor tubing isn't going to work for cooling in your climate, you need air handlers. If you look at the websites of sellers of air-to-water heat pumps, they all sell room-sized air handlers that start at about a quarter ton and go from there. I would recommend that over a central air handler and ducting, as it allows you to put each room under its own thermostat, with a central air handler you're kind of giving away the main benefit of hydronics which is pinpoint control.

    Hot water is going to be a challenge. Reading the WaterFurnace website, it says, "As a WaterFurnace unit runs, it can capture heat that would normally go to waste and divert it to your water heater tank (using an optional component called a desuperheater). Your unit can generate up to 50% of your hot water—at almost no cost." I read that to mean that it doesn't have the ability  to balance heating and cooling, just grab waste heat. So you need to have a separate water heater for when the cooling isn't generating enough waste heat to meet your hot water needs.

    Given that, I would recommend not trying to get hot water from the WaterFurnace in cooling season, and instead buying a heat pump water heater. It pulls heat from inside the building envelope so it provides cooling. It also provides dehumidification which is something you're going to want. I couldn't find an online price for the desuperheater option but I would be very surprised if it wasn't substantially more expensive than a HPWH.

  • hausfxr
    hausfxr Member Posts: 4
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    Thanks for the comments Jamie. I should have labeled the second diagram components - separate cooling blower system with new insulated piping going to each floor - this is what the DX guy we talked with suggested with refrigerant lines. We already have a night air cooling system on the top floor partially inside the insulated attic area and insulated ducts going going to each room, so a central air-handler will work with zoned dampered ducting. The main floor is one open space with only a separate powder room, so, one air centralized handler above the basement stair for that space. The finished basement is problematic, and we've strategized to have three (unfortunately they will each likely have to be oversized for the very well insulated spaces) separate blowers.

    All of the places an AHU will go, except one, have chases or room corners that can be enclosed and can easily accommodate pre-insulated pex lines. The DX contractor cautioned us that any refrigerant lines can't be pulled through too many corners and would have to have brazed segments in places - he wanted to run lines up the outside of 1909 home instead, and we said, no way. If we go back that way, we'll revisit the problems of refrigerant lines with too many turns - not as much of a problem with pex, however.

    Also, by chance, each space that will have an AHU will have drain pipe near it for condensation draining - all sink and shower/bath pipes go to a common vented P-trap below the basement floor (with access). After having two bathtubs overflow in my previous houses, I decided that baths with soaking tubs should have a floor drain that goes to the central sink-bath drain and trap - no worry about traps drying out.

  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hausfxr
    hausfxr Member Posts: 4
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    The separate cooling system is something we've come to accept. We love the in-floor heating and, if I can help it, we would never live in another place that does not have it. So we can live with extra costs for the comfiness of floor heating.

    That's good to know about the Water Furnace unit - I have not spoken with anyone who knows specifically how WF units work. It was in another posting that someone pointed out that our four-ton unit was reversible and could also provide DHW - I assumed that meant also being able to chill water while in the reverse mode. To help discern what is possible is why I'm posting here.

    My model number does not list it has having Hot Water Option, but the model number allows for it - you are saying it cannot create hot enough domestic water in any model? Can you point me to the web page for that?

    This is a page from https://www.waterfurnace.com/literature/5series/SC2506WN.pdf

    My model number = NSW050G10RCSS0DA

  • Harvey Ramer
    Harvey Ramer Member Posts: 2,261
    edited July 8
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    @hausfxr To bad you already have your Geo unit. Hydron Module makes a combo unit that would fit your situation perfectly.

    https://hydronmodule.com/residential-products/item/revolution-ct