Air to water heat pump in CT, Zone 5a
After some wonderful advice on here I have made the decision to go all electric with my new heating system. However, a contractor I spoke with gave me some interesting information that marries the heat pump with my desire to have hydronic radiators: the air to water heat pump.
I have spent a couple of days researching, including a few articles on GBA, but have not come up with any viable options. The Chiltrix seems riddled with problems, the Spacepak gets a boost from John Siegenthaler’s (sp?) ownership of a test unit in NY (but, while he recommends them in his presentations, I have not seen an update or a complete review by him), Aermec has been mentioned here as “the Ferrari” of AWHPs (gee, my son loves that!), and LG, Mitsubishi and even Taco seem to have really promising units, but not in North America – yet.
This is no doubt the future, but what of the present? Our current situation is fine – an efficient wood-burning fireplace insert and micathermic panel heaters do a fine job with heating our 1400 sq ft ranch – so I can wait a year. That said, it would be fantastic to have heat and be done with it!
What are your thoughts on air to water heat pumps in general? Any specific product advice?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I have one from Maritime Geothermal, Nordic AWHP. Had some issues but think it was more problem with Installer than the unit. Had to charge the unit at the beginning of the heating season so worried there was a small leak but not sure. Recently, changed a faulty sensor and working well now in Toronto climate.
Things to consider are noise and airflow from the outdoor unit vs. shorter distance of the runs, so placement is important.
Hi Jerry, thanks for your response. Can you elaborate on the noise issue? I was told it is the same as an air-to-air heat pump in sound.
Does the unit heat your home and provide DHW?
I can also provide feedback on the Nordic air to water units. We've been running an ATW-75 for ~1.5y in our newly built home in Boulder, CO (climate zone 5B). The unit has been trouble free, even when tested all the way down to -7F.
If you chose this route, depending on the size (tonnage) you need, you might consider adding a soft starter. While I was commissioning the system, I did notice some compressor starts could cause a momentary dimming of some of our LED lights. After confirming with Nordic that it wouldn't void the warranty, I installed a unit from Hyper Engineering (http://www.hypereng.com/). Soft starters dramatically reduce the initial current draw required to get traditional, single speed, compressor motors turning. The Hyper unit worked exactly as advertised - no more dimming lights. It was a 10 minute job that anyone with minimal electrical experience can perform. Nordic also told me that they sell the same unit. It may even be possible to have it pre-installed at the factory.
Noise wise, the system uses continuously variable speed outdoor fans. Our experience so far is that in cooling mode, the fans run slower and noise levels are similar to other ACs in our neighborhood. In heating mode, especially at sub-freezing temps, the unit moves a lot more air. I'd guess it's 1.5x a traditional AC unit. Our guest room is right next to the outdoor fan unit and, even when asked, we've yet to have a guest complain about the noise. We do have Alpen 7 series windows though (glass-film-glass triple pane) and thick R-35 Bensonwood OB+ walls.
I haven't played with it, but there is a setting in the PC based commissioning application to limit the max fan speed of the outdoor unit. I suspect this would allow you to trade off a little bit of efficiency for quieter operation.
As mentioned above, these units do not have a variable speed compressor as you'd see in a mini-split. Instead, they use a 2 stage design from Copeland that allows the unit to run at ~60% or 100% output. It does this by bypassing a portion of the compression cycle instead of changing the compressor rotation speed. Like water to water ground source heat pumps, Nordic expects that you will use an appropriately sized buffer tank to decouple the heat pump from the loads it will serve. In our system, for example, it is quite common for the heat pump to run for 20-40m charging up the buffer tank, and then sit idle for 2 or more hours as the heated/cooled fluid is distributed in the radiant floor system based on loads in the house.
The upside of this type of setup is that you can have total control of the heating/cooling in your house with no fan noise. The downside is cost and complexity. To execute this well, you need a good design (based on load calcs) and competent installers. To make our system work (and it does so flawlessly so far), I had to go out of state to find a designer and then carefully guide my contractor's plumber through the setup. I also had to fully understand and commission all of the controls (Tekmar 406 house controller + Tekmar 553 thermostats, also recommended). Hopefully you have more experienced help on hand. Getting the actual heat pump up and running was easy though. Any HVAC tech who has installed a refrigerant line set should be able to do it.
I forgot to answer one of your questions, "Does the unit heat your home and provide DHW?". Like most GSHP units, the Nordic ATW series has a de-superheater which you can connect to a DHW pre-heat tank. The allows you to divert some of the process waste heat to bringing cold water up towards DHW temps. You will always need a "finishing DHW heater" to complete the job, but temperature lift required by the DHW heater is reduced.
For our setup, we have a 50gal DHW pre-heat tank followed by an 80gal Steibel Eltron Accelera heat pump water heater. The finishing tank is set to 140F. This ensures that, even if the pre-heat tank sits for long periods at a temperature conducive to growing bacteria, any bacteria will be instantly killed when reaching the finishing tank. Our DHW distribution lines are downstream of a mixing valve that ensures 120F max temps at all outlets.
This is very interesting, and after an 800 word explanation on how simple the system operates and was set up, luckily because you the homeowner were the only one capable of commissioning, I decided to rip my Mitsu cold climate heat pump off the wall and give it a whirl.
any comments on maintenance of this system?
This seems like some steampunk contraption on LSD.
Best of luck
:-)
I don't know that my system is uniquely complex for a residential hydronic system. I'm sure that many installers of water to water GSHP systems and radiant floor heat would be right at home. The issue for me is that in my area typical radiant floor systems are high temp affairs served by boilers. Switch to using a heat pump and the "boiler/radiant guy" doesn't want to touch it. When I asked contractors about using the floor for radiant cooling (possible since we have almost no latent load in the cooling season in Boulder), they thought I was crazy. So, I had to work harder, and take on more of the work to get what I wanted.
As for maintenance, the system has been maintenance free so far. I did have an HVAC company come by for an inspection after our first year of runtime, but they just told me a few items I should check periodically myself (expansion tanks still have air in them, clean the outside coil, look for water leaks, etc.), asked me to call only when I noticed a problem, and didn't even charge me for the visit. That was definitely a first.
Wonderful review of your system! I will be installing Alpen double panes, so thank you for confirming that decision, too.
I can only offer my opinion, which isn't much.
Why make things more complicated than need be. In the end don't we just want reliable, efficient, safe and comfortable heating and cooling.
...but some people want something to tinker with all the time, some want to complain about something, some think expensive means better.
I rather drive a four banger across country that's proven than some 60 valve, ten cylinder Ferrari that likely spits parts out constantly in its claim of high performance, has a weak supply and service commitment.
In New England it's very common for houses to have radiator heat and no cooling. The fuel of choice is heating oil. In a system like that it's far simpler to replace the boiler with an air-water heat pump than to convert the entire house to forced air.
Not much data, but I've yet to see someone describe a Chiltrix problem that wasn't caused by not following the manual. Including sending the design to them for review.
Excellent point and food for thought, Jon R. Thank you.
Jennifer, reaffirming Jon's point above - my Chiltrix install in zone 4a has worked without a single hiccup from day 1. Following the manual (easiest) or having low-temperature hydronics knowledge and experience (rare to find) is essential in any successful AWHP installation.
Exactly Jon!
It's human error. Our thinking is we need more complexity in all things, but...
Installers still dont follow the manual, framing crew doesn't adjust depth of nailing, or someone didn't roll the zip tape properly.
We're about to embark on commercial flights to space, yet we lack high-speed internet in much of rural America, and I'm still getting safety recalls on a vehicle that is eleven years old.
My understanding is that Dandelion Energy is now or will soon be serving some of the CT counties nearer the NY border at some point in the next couple of years. It's probably worth seeing if that's an even remote possibility in your ZIP code (even though I don't believe they're doing hydronic GSHP systems yet.):
https://dandelionenergy.com/see-if-your-home-qualifies
Dana, a contractor came out this week and said that they are having lots of issues with GSHPs in my area. Not sure why, exactly, but I am hopeful for the AWHP, as it sounds like the best of both worlds.
Justin Gibbs,
We are in Longmont, CO and contemplating a Nordic ATW for our near net zero house.
Your last update is a couple of years on now and we are wondering how you are finding your Nordic's performance now that you're going on 4 years installed?
David—
Is your system in place and running well? I am also thinking about a Nordic ATW, and would love a 👍 or 👎 on your experience!