Mixed Hydronic & Forced Air Control Strategies

CuriousKurt

I debated where to post this question and ended up here on the Main Wall given that it's a mix of radiant, mini-splits, controls, and theory.

New to the forum, Hi !
I'm building a home in Philadelphia which will have two separate Mitsubishi multi-zone heat pump systems for a total of 4 discrete zones. It also has radiant heat in the floor of the main living area. My question is, what options do I have for integrating the control of the two heat sources? I'm also interested in the general strategy and thinking around how to elicit the greatest comfort from the two heat sources.

The home is 3 floors, roughly 2100 sqft and and the main living space is on the second floor. We can ignore the 1st and 3rd floors which are serviced only by the Mitsubishi heat pumps. The second floor, an open floor plan with forced air and in floor radiant is the one I'm curious about. The home has large sliding glass doors covering about 70% of the external non-shared walls. [In Philadelphia row houses share walls with their neighbors. I share my north and south walls with neighbors]

Based on the amount of glass I felt that having a radiant source to offset the window losses would help create a more comfortable living space. Now that I'm getting closer to installing everything, I'm wondering, what controls can I use that will work with the Mitsubishi unit and the hydronic system to assure that both systems are playing well together.

Help, feedback and questions are all very much appreciated.

Thanks!

STEVEusaPA

Mixing Forced air and radiant to heat the same space is problematic, to put it nicely. Why both?
Using only radiant for heat is most comfortable.
What boiler is driving the radiant?

CuriousKurt

Why both? The heat pump systems provide cooling during the summer months so ducts had to be run to all areas. I added radiant in order to offset the heat loss of all the glass, it's a comfort driven decision; I like the way radiant feels vs forced air.

The radiant system will be supplied by an electric packaged boiler (20k resistive heat tankless with a 2.2 gallon tank integrated). It's an Electro Industries EB-MX-20.

TAG

So you have two compressors ... each with two heads?

What type ? .... since I'm hearing ducted .... are they the pizza box type or the larger air handler type.

GW in New England seems to use the integrated control -- maybe he will chime in.

I have mixed both -- in fact my home in chestnut hill has ducted/radiant/radiators and mini-splits. The ducted needs to be zoned ... but with the mini .. you have that.

I set my radiant just under the set point and use the ducted and mini splits to even out the temps -- including spaces with radiators. Unfortunately -- my ducted system is by Carrier and the Mitsubishi use a Honeywell system. The Mitsubishi is cloud controllable. The hydronic is Buderus ...

Zman

How important is efficiency?
How is the radiant installed?
The radiant is going to be way more expensive to run.

Jolly Bodger

Electric boiler? Ouch! Now I see why you want to use the minisplits for heat. I would set the radiant as low as comfortable (68ish?) and heat he space with the minisplit. The splits are 4x more efficient than the boiler.

SuperJ

You can get a adaptor to allow a 3rd party thermostat to control the Mitsubishi heat pump. You could use a multistage stat and stage the radiant however you want.

Think about air flow/duct work with the heat pump. I have a cold climate wall mount and wish I would’ve thought about the air flow patterns more. The space is at setpoint, but since I’m not washing the perimeter wall with heat it feels colder than it should for the air temperature it’s at.

hot_rod

If you want radiant to run when the minis are, maybe control it with a floor sensor. Or a sensor on the return. If it has ODR function you may be able to dial it in to run continuously at a low boiler setting. Pump runs 24/7 boiler cycles in and out
Maybe add a programmable function

It will cost $$ to run electric heat

pecmsg

One season operating that electric boiler and you'll stop using it.

High Efficiency NG or LP boiler (even oil is better then electric) too keep the floors warm and offset the defrost cycles of the heat pumps and let the heat pumps warm the house!

CuriousKurt

TAG said:

So you have two compressors ... each with two heads?

- Sorry I misspoke, that was the original design but, we changed during early construction. Due to the change, my concern is that I'll experience a condition where the ground floor temperature is not well maintained during heating season. Hopefully, I can do a better job explaining this time.

TAG said:

What type ? .... since I'm hearing ducted .... are they the pizza box type or the larger air handler type.

• The system is a Mitsubishi HyperHeaat 4 zone using an MXZ-4C36NAHZ outside.
  
• The 3rd floor - Inside, ducting has been installed for an MVZ-A12AA7 multi-position air handler on the 3rd floor. This system supplies the upper level where bedrooms are. It's a single zone. The 3rd floor does not have radiant so it's fully supplied, summer and winter, by the Mitsu system.
  
• The 2nd floor - Another MVZ-A12AA7 multi-position air handlers services both the 1st AND 2nd floor as a single zone. the 2nd floor ALSO has hydronic radiant beneath hardwood flooring.
  
• The 1st floor - Serviced with forced air via the same air handler as the 2nd floor.
  

My concern is that when I provide heat via radiant the AH will not run and the ground floor will become uncomfortably cold. I had hoped that there was a control system that would mix the two using the forced air as the primary heat source and then augment that with a small amount of radiant to offset some of the losses due to all the glass.

The system was designed by a competent passive house engineering firm. Then, I made changes during construction resulting in this odd condition. The original design called for a ceiling cassette on the first floor that would be it's own zone. I changed ceiling layout and that's no longer an option.

We're in late stages of construction. My builder, mechanical installer, and wallet would kill me if I made another change at this point but, if one has to be made it's better now than later.

TAG said:

I have mixed both -- in fact my home in chestnut hill has ducted/radiant/radiators and mini-splits. The ducted needs to be zoned ... but with the mini .. you have that.

I set my radiant just under the set point and use the ducted and mini splits to even out the temps -- including spaces with radiators. Unfortunately -- my ducted system is by Carrier and the Mitsubishi use a Honeywell system. The Mitsubishi is cloud controllable. The hydronic is Buderus ...

I'm hoping to find a strategy like this but, concerned that it'll be a constant struggle to find real comfort. I'd like to have a house that I can program, set, and forget.

CuriousKurt

Thank you for all your feedback!

I typed a complete response, posted it, chose to edit a typo and when I saved it disappeared. What a bummer.

I'll reply again later when I have more time. Again, thank you for all the feedback, suggestions, and critiques; I appreciate it.

Erin Holohan Haskell

@CuriousKurt, sorry about that. Your comment got held, but we've restored it.

TAG

So the Mitsubishi is actually running two air handlers -- that's all -- no other heads .... correct?

I actually do see an issue unless you are lucky and the reduced operation of the main floor Mitsubishi system (while the radiant is heating) is still providing enough heat to the lower level #1. I'm not sure how Zoning is integrated into those units -- that would solve the problem.

Is #1 a ground level w/ basement under --- or is this the actual street level. I used to live in CC .. still own property and with houses on two sides the heat load is low .... I had a large kitchen with bump out to the back yard w/ glass .. that needed more heat. The lower level in the old basement had a low heat load.

Both of my Mitsubishi setups are the same family as you are using outside. Hyper heats -- in my case they are both 30k units running three 12k heads inside. One house has three wall units -- the other one wall and two ceiling. Yes, you can have more head BTU's vs the outside compressor value.

I had thought of using the air handler that you are using but it was so new a couple years ago ... that's why I went with the Carrier multi speed unit. I could not get good information -- at the time the blower only had three speeds.

I'm building a new house in Bucks County -- again with some Mitsubishi mini splits -- But I'm using the Carrier system again vs running the air handler you are using. I just could not get good info on how to use the Mitsubishi air handler .. I also wanted propane furnace for backup.

I think you need to ask the designer -- If/how that lower setup can be zoned. Figure out what each area needs -- and then factor how you can have the system zone off the main level when the radiant is providing some/ all of the heat.

This is why I used the Carrier 5 speed air handler with thee zones in my current property -- when the radiant goes on the Carrier system has thermostats in each zone and will modulate depending on what the space needs -- or does not.

There is a way to zone the Mitsubishi -- but they keep making advancements .. so it may have changed. With it all modulating there must be a way to have some zoning capability -- two trunks w/ zone dampers to each level .. thermostat on each level.

CuriousKurt

TAG said:

So the Mitsubishi is actually running two air handlers -- that's all -- no other heads .... correct?

There is a way to zone the Mitsubishi -- but they keep making advancements .. so it may have changed. With it all modulating there must be a way to have some zoning capability -- two trunks w/ zone dampers to each level .. thermostat on each level.

Again, thanks for the feedback.
Yes, two heads. I may add another later for the garage / workshop but for now just the two. So yes, I could put a standard wall mount split on downstairs on the ground level and call it a day.

My home is not like most center city rows, I combined two lots and have a funky shaped building spanning the two. It's not particularly large as I have a center outdoor courtyard on the 2nd level with glass facing it. Sorry it's not easier to visualize.

As you suggest, I'm hoping that the load for the lower level will be low enough that it just naturally balances out. Zoning the Mitsu air handlers is probably not as easy as adding a damper as they have a fairly tight spec for static pressure if you want to get good performance out of the system.
The lower level is slab on grade, no basement but, due to the shape of the living space it's a small number of square feet and I did a 3" closed cell foam barrier between the slab and the office which is raised up 24" off the slab. Again, I'm hoping load will just work out. I also have an ERV in the mix so air circulation throughout the house will be constant.

The engineering firm that designed the mechanical systems is great, they are a leader in the Passive House space and do quality work. However, I'm a dope and I made changes during construction that messed with their design and had I followed the plans this would not be an issue.

CuriousKurt

Erin Holohan Haskell said:

@CuriousKurt, sorry about that. Your comment got held, but we've restored it.

Thank you!!!

CuriousKurt

Zman said:

How important is efficiency?
How is the radiant installed?
The radiant is going to be way more expensive to run.

Efficiency is a consideration but, not the only focus. I selected highly efficient triple pane windows with coatings to reduce solar gain and the doors are top of the line energy-wise. The house is well sealed, covered in 2 inches of external rockwool, and internally insulated with a mix of closed cell and glass depending on the location. The roof is a mix of rigid polyiso and glass and IIRC over R50. Even the garage is well insulated.
I opted not to have any gas/oil in the house focusing on use of electric from renewable sources including rooftop PV solar. So Yes the electric boiler is a hog, but the primary heat/cool source, the Mitsubishi HyperHeat system, is about as efficient as they come. And the total load should be reasonable.

The radiant is in-slab for the garage, an area I haven't said anything about since it wasn't applicable to the thread topic. And the 2nd floor living space radiant is going to be wood floor over subfloor with pex stapled up using aluminum heat spreading plates. Insulation in most areas is IR reflective foil faced R39 with a 1" air gap between the foil and the pex to allow for proper IR reflection without turning the insulation foil into a heat conductor.

CuriousKurt

Jolly Bodger said:

Electric boiler? Ouch! Now I see why you want to use the minisplits for heat. I would set the radiant as low as comfortable (68ish?) and heat he space with the minisplit. The splits are 4x more efficient than the boiler.

You're thinking the same way as me, I want to do the majority of the work with the heat pump and augment with radiant for comfort. I was hoping to find a control system that would allow me to program proportional targets and dial it in once and then forget about it.

CuriousKurt

SuperJ said:

You can get a adaptor to allow a 3rd party thermostat to control the Mitsubishi heat pump. You could use a multistage stat and stage the radiant however you want.



Think about air flow/duct work with the heat pump. I have a cold climate wall mount and wish I would’ve thought about the air flow patterns more. The space is at setpoint, but since I’m not washing the perimeter wall with heat it feels colder than it should for the air temperature it’s at.

I feel like I've seen references to this, the name that sticks in my mind is something like RedLink but, can't be sure. I thought, that if I used a 3rd party stat for the Mitsubishi units I'd lose some of the 'intelligent' functionality but, I might be making that up...

Jolly Bodger

@CuriousKurt if you are making your hot water with electric resistive. And the purpose of the infloor is just for comfort and not the primary heat source. Why not install electric infloor instead of hydronic. Install cost would be a lot less, and would work fine with your install method. I believe it would be a lot more efficient as well. Control would be a matter of coordinating the setpoints.
If you are set on hydronic infloor, why not a air to water heat pump like Sanden SanCO2?

CuriousKurt

hot_rod said:

If you want radiant to run when the minis are, maybe control it with a floor sensor. Or a sensor on the return. If it has ODR function you may be able to dial it in to run continuously at a low boiler setting. Pump runs 24/7 boiler cycles in and out

Maybe add a programmable function



It will cost $$ to run electric heat

Yes, the boiler does have Outdoor Reset functionality and is able to modulate the heat elements to deliver the target temp adjusted by the outdoor reset ratio.

CuriousKurt

Jolly Bodger said:

@CuriousKurt if you are making your hot water with electric resistive. And the purpose of the infloor is just for comfort and not the primary heat source. Why not install electric infloor instead of hydronic. Install cost would be a lot less, and would work fine with your install method. I believe it would be a lot more efficient as well. Control would be a matter of coordinating the setpoints.
If you are set on hydronic infloor, why not a air to water heat pump like Sanden SanCO2?

The radiant PEX is already in; no going back now.

TAG

Sounds like you have done the work up front to make the space energy efficient -- tight. The wall units use a wireless handheld -- it you want some sort of overall control with internet -- it's an add on system. The ceiling/floor and ducted use either a wired or again if you want the overall control ... you need to buy and plug in the module to each. Mitsubishi uses a Honeywell system -- I can control the thermostats with an internet app. It has uses a router -- all the units talk to the router.

How is the air handler controlled? I know they were coming out with a more advanced app .... same thermostat. The surfaced mount wall units have the most optional controls ... they really are slick.

I would try and see if the designer knows some way to zone that 1/2 floor unit .. don't see how else you can make it work. I'm surprised it's not in the system to begin with -- trying to heat/cool two levels like that is hard anyway.?

CuriousKurt

TAG said:

I would try and see if the designer knows some way to zone that 1/2 floor unit .. don't see how else you can make it work. I'm surprised it's not in the system to begin with -- trying to heat/cool two levels like that is hard anyway.?

The engineered design called for discrete forced air zones for floor 1 and floor 2. I foolishly made changes to the floor plan of the first floor making it impractical to use the ceiling mounted cassette that the engineer called for.
The situation I'm in is all my doing, the engineering firm did a great job up front.

When we get closer to finishing the house I'll reach out to see if they have any suggestions.

As long as I can control the systems via a common means, I'm sure I can make it work. Though, I'd rather not reinvent the wheel if I can just go out and buy one.

CuriousKurt

Jolly Bodger said:

@CuriousKurt
If you are set on hydronic infloor, why not a air to water heat pump like Sanden SanCO2?

I didn't know that split units existed. I skipped buying a heat-pump water heater because I didn't want to cool my garage / workshop just to heat another part of the house.

That Sanden setup is pretty slick and if they get anywhere near the claimed efficiency it could have a reasonable payback period unlike some other high-efficiency devices.

Thanks for bringing it to my attention, I'm kinda bummed I didn't know about them before purchasing the existing boiler.

Icarus

My guess is that even if you trash the existing boiler, using the Sanden will pay for trashing the electric boiler in a couple years...No brainer. I am working on a project to convert a CI nat gas boiler to be fired by a Sanden. Still looking for some more info.

In your case, even if you don’t want to go with a Sanden CO2 heat pump, there are others that use conventional refridgerant that might be more efficient at radiant floor temps (<120F) rather than the higher temps needed for CI radiators, as high as ~170 or so depending on OAT.

Icarus

PS. There is a very good thread on this forum on Sanden using it for both CH and DHW, along with the studies that show how efficient they really are.