Low temperature baseboards with geothermal

Based on Doc's comments about my desuperheater thread, and other aspects, I've started to rethink my geothermal setup.

Considering my house currently uses hydronic baseboard heating (currently using an oil boiler) across all three floors (2nd story, 1st story, finished basement) and ducted central air (2nd story, 1st story), I'm now instead considering the Hydron Cruise Variable Speed Water-to-Water unit... anyone have any experience with these types of units? Per Doc's idea, this unit could also produce domestic hot water for us in addition to the heating and cooling. Seems like a truly all-in-one solution.

We would put an air handler in the conditioned attic (ceiling close cell spray foamed) and use the existing ductwork for cooling. While the ductwork could be improved, we're in Massachusetts and cooling is definitely the less critical aspect of our climate control.

I would replace all existing baseboards w/ low temperature baseboards. The Hydronic Heating Technologies Inc. Eco-Con caught my eye, but I see there are a number of other brands too. I'm sure I'll need to do some math on if I can do a one-to-one (i.e. linear foot match) swap out of the existing baseboards w/ the low temp ones. I expect this also depends on outputted water temperature and flow rate.

All that said, does anyone have experience w/ low temp baseboards? If so, on average, do you find you need more or less linear feet of low-temp baseboards to cover the current heating load?

This really seems to be a great solution for those who currently use hydronic heating w/ typical baseboards and want to go geothermal.

Thanks for reading and cheers.

 

https://www.waterfurnace.com/residential/products/geothermal-heat-pumps/504w11

 

Hmmm. I guess with this unit, there's the possibility I don't even need to upgrade my baseboard radiators. I'll confirm how they run in the dead of winter w/ the water temp set to 140 to 150F. Given it is an oil boiler now, I expect the water temp is closer to 180F. I actually haven't even moved into the house yet (next week), hence my not having data from this past winter.

Thank you for the reply.

 

You might want to consider the "direct to Load piping", getting you 10F warmer water to the radiators.

 

Thanks again for your willingness to share your expertise.

 

Doc, given your favorable view of the Waterfurnace 7 Series, do you think the Hydron Cruise variable speed water-to-water system is a solid investment and ready for primetime? I remember you saying on another thread to focus on performance over saving some money upfront. Because of this, I'm thinking maybe I should try for the variable speed water-to-water system and upgrade the baseboards to low temp baseboards, instead of going with the Waterfurnace 504W11.

The 504W11 would presumably allow me to keep the original baseboards, but I'd also need to buy an additional two tanks for domestic hot water, bring the total tanks needed for that system to three (compare that to one tank needed w/ the Hydron).

On top of that, the Hydron Cruise (variable speed compressor) should run more efficiently than the Waterfurnace (single stage). I've seen some apprehension on variable speed compressors, both water-to-air and water-to-water... but this has only been theoretical concerns by contractors I've spoken with. However, the empirical evidence seems to suggest these systems do indeed work and work very well.

 

I believe you still need a second tank for DHW, internal heat exchangers that will have water from the heat pump circulated through them.

 

Attached is a Optiheat with DHW. 2 tanks. Credit to John Manning at Phoenix Energy Supply for the drawings...

Your question is a tough one. The Hydron is a new unit, and I like the water-water variable speed concept. But the problem is that it is a new unit, and it might be prone to bugs a mature unit does not have. Plus it is utterly expensive.
In general lowering your water temp via higher efficiency baseboards is a good idea.

Just don't know if all of this is very cost effective. You mind get their cheaper with a good outdoor reset.

 

Okay, so I've been crunching some numbers and this has led to more questions for the experts (for the record, I've become addicted to this forum). I believe I wanna go with the recommendations made here of the Waterfurnace Optiheat 504W11 and tie it in to the existing baseboards (which I intend on upgrading to low temp Smith HE2 baseboards myself) as well as the existing ductwork for cooling.

Disclaimer... this post has quite a few pasted images, but I summarize these in my text if you wanna skip thru. Thanks so much for anyone's review. I've underlined and bolded my questions for reading ease.

First off, the room-by-room Manual J for my 2-story 3468sqft 1968-built colonial (has finished basement that is >80% below ground level) is 55.8k BTU/hr. The basement heating load is just 5.6k BTU/hr.... does that seem low?? I'm located in Sherborn, MA (halfway between Boston and Worcester). I had the attic close cell spray foamed to R38 and the gable ends to R21... this is already built into the Manual J. Of note, this Manual J was done with a water-to-air system in mind, whereas I will now be doing water-to-water. Here's the full Manual J (a lot of details, apologies):






Lately, I've been improving the house insulation and tightening up air infiltration around doors and windows.

I also calculated my estimated heat load by using my last oil fill (123.6 gallons), using the HDD for my area during the period from the previous oil fill to this most recent one (943), and assumed a boiler efficiency of 70% as it is the original boiler that came with the house (50 years old). Given a 65F base temperature, a 6F design temp, and a 70F set temp, I got a heat load of 34k BTU/hr. This is compared to 56k from the Manual J. Can this really be the case?? If so, this would drop me a full size down for the Waterfurnace!

Lastly, I crunched numbers for the room-by-room heat output from my baseboards as well as what it would be with the new low temp baseboards:

Slant Fin Baseboards


Smith HE2 Baseboards


Under the assumptions of the Manual J, I can meet the heating loads around 130-135F when using Slant Fin baseboards. In fact, I can get away with about 110F water when using the low temp Smith HE2 baseboards. Given these lower temps needed, should I still stick with the Waterfurnace 504W11 and its ability to output 150F, or go with a more traditional water-to-water heat pump?

I know this post is a lot to go through, so huge props and thanks to all for your review. You guys rock!

 

I think I made some mistakes. My 34k BTU/hr heat load represents an average between tank fills. This is not the peak heat load the system needs to be sized for. It will also be good to accumulate more oil use data through the rest of the winter. We keep the heat at ~64 when home, ~61 when asleep, and ~59 when away.

An additional detail I forgot is that my domestic hot water is indirect using the oil boiler and a 50 gal converted electric tank.

 

Looks like I'm striking out trying to find an installer willing to do this system. I've asked three so far. Everyone wants to do water-to-air systems and run new ductwork. This is just going to be too invasive to our home and prohibitively expensive, given we'll likely need an all-in-one unit and a split unit to reach all parts of the house.

Does anyone know of anyone in the Massachusetts area that installs the Waterfurnace Optiheat 504W11? Also, does anyone have any empirical data on how well this works with baseboard radiators?

Thanks all.

 

The Hydron Cruise Variable Speed Water-to-Water unit sounds like a good fit for your application, especially of the system is not zoned in which case you could get by without a buffer tank. One thing that would concern me is the load side GPM requirements of the Cruise being kind of high, but if the unit varies that decently well, it might not be an issue. One of the flat and shallow reset curves would probably work for you application.

Have you considered keeping your oil boiler and hot water system as a backup (and DHW top off to 140 degrees with thermostatic mixing valve) and auxiliary heat for the new water to water unit? Polar vortexes and multiple heat sources go together.

The Cruise installation manual seems more concerned with selling zone controls and thermostats although the Cruise will work with any thermostat or control system that acts like a thermostat while the Cruise sets the supply target temperature with the reset curve.

 

WF Opti. We have installed about 30 of them, if paired with a direct to load piping, they work very well with baseboard radiators.
The Hydron is quite expensive, not sure if worth it.

 

My recommendation for the Cruise is a little self serving as it would be nice to get some reports from home owners and how the install goes and how they perform. The big range of modulation is a plus and will hopefully cut down on cycling noise.

I assume the AC unit would be replaced with a hydronic air handler?

Natural gas available?

Some of the under radiated rooms could have the baseboard changed out to low temp or insulation increased to balance the radiation and heat loss of the rooms. A few panel radiators could do the same.

 

Are both units reversible for cooling?

 

Thanks for all your thoughts, everyone.

I considered the Hydron variable speed water-to-water unit but there thoughts here and amongst a couple of geothermal installers I contacted was that it is too new of technology and not adequately field tested yet. I guess it is very expensive as well. I do wish there was more field data as well. I can't find any reviews on it. Even if we did have info on current installs, there would be no long-term data on it for years yet I suppose.

My hydronic system has three zones (basement, 1st fl, 2nd fl) with the 1st and 2nd floors each having two hydronic circuits.

If I kept my oil system as backup, I wouldn't qualify for the Mass state rebate. Instead, I was thinking of putting an electric heating element in the hydonic air handler, which feeds ducts going to the 1st and 2nd floors. And yes, I would be replacing the existing AC air handler with the Waterfurnace NAH for cooling (and back-up heating).

One more question: A lot of the copper pipe feeding the 2nd floor baseboards is run in the exterior walls... are there serious heat losses due to this I should be concerned about? I need to check which side of the in-wall R11 fiberglass it is on... hopefully the interior side.

 

I saw Doc recently mentioned sizing the system for the cooling load and then supplementing the heating load with electric resistance strips in the air handler. While the 066 model 504W11 Optiheat can handle 100% of my heating load (spec'd 56.5k ground loop vs. Manual J 55.8k), it overdoes it with the cooling load (spec'd at 54k ground loop vs. Manual J of 34k). Given this is a single stage compressor, I'm kinda worried this unit will be cycling on and off a lot during the cooling season and won't properly dehumidify. Is this something the outdoor reset would handle?

Additionally, with all the recent basement insulation chatter, I checked mine (finished basement) and it is underwhelming at best. Nothing in 3/4 walls and the 4th has fiberglass batts. Not surprising this is the zone that calls for heat the most. Gonna be digging come the spring to put some EPS panels against the exterior foundation. Locally, we have a couple places that sell reclaimed insulation for 50-75% off. Not bad.

Thanks all.

 

I believe he was talking about water to air systems, water to water systems have a buffer tank that should keep the unit from short cycling.

 

I was quoting an IGSHPA manual stating that geo systems should be sized for cooling, and the rest of the heating load should be supplemented with electric resistant heat. I strikingly disagree with that!

With your load numbers, I would put in a 5 ton optiheat, and move on.

 

Gents, new user here but my needs are strikingly similar to Brad's above.

To be clear, is the suggestion above that Brad a) get the 5 Series 504W11 with OptiHeat Technology and outdoor reset, b) connect it to the existing base board and cast iron radiators with direct-to-load piping for heating needs and c) replace the existing air handlers with suitable air handlers.

A few follow up questions:
1) Since the heating load determines the tonnage of the unit, the cooling load is bound to be oversized, but that should be okay since there are efficiency losses associated with the additional stage associated with cooling, right?
2) Can this system work with two air handlers and can they be zoned separately (i.e. programmed by different thermostats)?
3) Is there the possibility to design this system so my existing (brand new) natural gas fired boiler stays as back up?
4) Also, Brad did you get any solution that addresses your concern about short cycling in the cooling season and the resulting humidity concerns?

Brad, any updates since February on your approach?

Regards,
Vivek from Westchester County, New York