I've been lurking around the forum for a while enjoying all the knowledge shared on here so let me start off by saying "thanks". Lots of good information here. I'd like to tap into the brain trust for a little help. I am planning the mechanicals for our new home, and had the idea of using a geothermal WTW heat pump for the radiant heat in the floors. Instead of having two systems installed, I thought of putting in hydronic air handlers instead of DX air conditioning and switch the water flow using diverter valves in the cooling season. There are a couple of reasons I wanted to go the hydronic route. First, we are building a timber frame, and I don't want any exposed ductwork or awkward chases, so I planned in mechanical spaces to house air handlers and heat pumps. Second, I would rather have insulated synthetic water lines running through the walls than copper lines full of expensive refrigerant. The system I drew up actually has the system broken down into 2 heat pumps each with it's own thermal storage tank valved so that they can either be both heating, both cooling, or 1 of each (shoulder seasons in the mid-south sometimes demand using both modes periodically). I guess this leads me to a couple of questions: 1. Is this a feasible idea? 2. Are there any commercially available controls that will support this? 3. Why do all the HVAC guys look at me like my nose is growing out of my forehead when I mention it? (it's not... I checked) -Dan

If you don't want ductwork check out the multi aqua wall heads, they are like a ductless wall head but a bit bigger. We have used them for cooling on radiant floor systems with a reversible,(heat pump) WTW unit.
What you want is possible, you just need a knowledgable installer. http://www.multiaqua.com/ These are all hydronic cooling so no refrigerant except in your heat pump and as long as your OK with the looks no extra mechanical areas needed. We run multiple units off one heat pump and storage tank to save costs. Keep in mind a typical 50-80 gallon storage tank can be switched from heating mode to cooling mode in as little as 30 minutes with $.20 or less in energy costs so unless the home is 5000 sq feet and needs two systems your idea should be feasible with one WTW and one storage tank.

Tekmar 406 is the control you want. It will even permit some radiant cooling (while monitoring dew point to avoid condensation damage).
It is a must to design radiant for low temps.

Thanks, SkyHeating. I don't have any problem with ductwork in general (we'll have it in the basement for the basement and first floor cooling). but we have 4 rooms on the second floor that need to be attended to (2 on each end of the house with the vaulted great room ceiling in between). To address this, I planned in 2 small attic spaces which can each handle a small air handler, with an energy recovery unit for some outside air exchange since the building envelope is going to be so tight.

Any thoughts on good hydronic air handlers for cooling? One installer stated that you can't cool a house in the south with hydronic because it won't pull the humidity down... seems kind of odd to me as it's done regularly in commercial systems. I was looking at the spacepak units, but can't seem to find any real-world feedback on them.

the house is rather large, almost 5,000 sf. 8" ICF foundation with a 2-story timber frame above. I was planning to put the radiant heat loops in the basement and first floor, then an air handler in the basement for the basement and first floor cooling, and 1 smaller air handler in each of the planned attic spaces for the 2nd floor cooling and air exchange.

someone else suggested a "triple function" unit in the basement to handle the radiant heat and lower levels cooling, then two small (1 ton) water cooled package units for the upstairs. Any thoughts on that idea? Somehow when he said "triple function" it looked like there were little dollar signs flashing in his eyes.

On the geothermal loops, I have a few options. First, we have a very good producing water well on our land (50+gpm refill rate) which i was told we could likely use to supply an open loop system. Second, we have plenty of room to run horizontal loops or drill wells for closed loop. The third option is to dig a pond and put coils in there (or let the open loop from the well dump to the pond.

-Dan

Joe:

Thanks for that info. I must have been typing at the same time you were. I'll dig into the Tekmar 406.

-Dan

can't cool a house in the south with hydronic because it won't pull the humidity down...

You can operate it at a temperature where condensation won't occur, but this won't be very comfortable. Or you can let condensation occur, but use a radiator/fan coil design that collects/drains the water. Visually, I think that in-wall or in-ceiling cassettes look best.

http://www.aermec.us/index.php/products/fan-coils/recessed-wall-fan-coils

2 heat pumps ... both heating, both cooling, or 1 of each

I wouldn't do this. One heatpump can simultaneously produce hot and cold water.

All good heating & cooling system designs start with the room-by-room load calculations. Have you nailed those down with any confidence yet?

"The south" covers a pretty broad range of climates and conditions- got a zip-code?

jonr- The issue with hydronic cooling is as much (or more) managing condensation formation on the distribution plumbing/manifolds as it is managing the the condensation at the coil (which is much easier.) Insulating the pipes can be pretty straightforward and reasonably air-tight, but the manifolds are still a problem.

managing condensation formation...but the manifolds are still a problem.

Seems like condensation on one manifold in a utility room would be pretty easy to deal with.

You can operate it at a temperature where condensation won't occur, but this won't be very comfortable. Or you can let condensation occur, but use a radiator/fan coil design that collects/drains the water. Visually, I think that in-wall or in-ceiling cassettes look best.

That was my plan to use a fan coil design that incorporates a condensate pan and drain line, not depend on the radiant floors for primary cooling/humidity control. Using a properly sized chilled water fan coil with a condensate drain, is humidity still be an issue?

I wouldn't do this. One heatpump can simultaneously produce hot and cold water

Is this a product line that has both hot and cold circuits, or would this be using the source loop for the hot water supply? I'm not sure I follow.

All good heating & cooling system designs start with the room-by-room load calculations. Have you nailed those down with any confidence yet?

I have not nailed down the load calculations yet.

"The south" covers a pretty broad range of climates and conditions- got a zip-code?

for sure... 30277

managing condensation formation...but the manifolds are still a problem.


Seems like condensation on one manifold in a utility room would be a pretty easy to deal with.

I had been considering this, thinking that the manifold would be relatively easy to insulate with properly fitted and glued insulation (I came up on the industrial side... I like a nice clean looking insulation job).

-Dan

Is this a product line that has both hot and cold circuits, or would this be using the source loop for the hot water supply?

The latter (although I suppose a desuperheater loop counts as the former). The plumbing, buffer tanks and controls are probably somewhat complex (or at least interesting).

In 30277 the mid-summer outdoor dew points average about 70F, with peaks in the mid to high 70s:

http://weatherspark.com/#!dashboard;a=USA/GA/Sharpsburg 

(Pull up a dew point graph from "Graphs" pull down tab at the upper right, and use the slider to scale and zoom to cover a full summer.)

You'll need to get the indoor dew points much lower than 70F to be able to even get much sensible-cooling out of hydronic systems. To keep the mold & fungi from feeding off the humans it's better to get the indoor dew points at least down to 60F, if not 50F. You have substantial latent loads to contend with that folks in the much drier southwest rarely have to address.

I agree - no higher than 60F for an interior dew point when the indoor temp is 75F. What does that translate into for required fan coil coolant temp - perhaps 45F (when outdoor humidity is high) and 60F (when low)?

It looks like chilled radiant floors combined with good air sealing (which ensures minimal latent loads even if it is humid outside) and ERV/DOAS system delivered dehumidified air is a viable (and probably superior) radiant cooling design. Ie, small ducts and a very small ducted, low temp AC for latent loads and the floor for any remaining sensible loads. Caution - you do not want to open the windows with this design and concrete slabs. Massive cool objects and humid air don't mix well.

So am i correct that properly sized fan coils and chilled water system will handle the loads regardless of humidity (as long as the humidity is properly accounted for in the calculations)? That's what I can't wrap my head around is why several guys around here have told me "it can't be done". One geothermal "specialist" (had the nicest truck and best sales literature) told me water is not a good heat transfer medium... as he's trying to sell me a horizontal loop system piped into the low lying wet area downhill from the house site

I'm convinced that fan coils would work and radiant floors/walls/ceiling would work with DOAS dehumidification support. But I wouldn't be surprised if a hydronic system ended up being more expensive. And that qualified installers would be very hard to find (or expensive).

As Dana pointed out a room by room load calc is your starting point.The issue on an infloor radiant cooling system is controlling delivery temperature in order to maintain space dewpoint.The slightest error and condensation will form on walls ,floors and ceilings.Ehaust rates and infiltration along with occupant loads can kill this idea if not designed correctly.The use of chilled water coils will simplify the engineering because the size of the coil along with the chilled water temperature can do a much better job handling the latent loads.If you decide to use slab cooling then I would strongly recommend a seperate dehumidification system to aid in controlling the humidity.

a room by room load calc is your starting point

I encourage you to use an iterative approach. For example, pick some generally accepted but on the high side insulation and air sealing levels and then look at the loads, HVAC needed and operating costs. Then go back to step one and try some variations to see if there is something that is better overall.

a room by room load calc is your starting point

Okay... so I finally got around to finishing up my room load calcs.

My constants for this calculation were:

Summer Temp 95F
Winter Temp 23 F
Summer moisture: 100 grains

Indoor summer temp 72 F
Indoor winter temp 75 F
Indoor RH: 55

Here's what I got with based on "Average" construction methods and air infiltration ( I won't bore you with the room by room, floor by floor numbers):

Square feet (whole house): 4868
Sensible heat gain (BTU/h): 29,889
Latent heat gain (BTU/h): 8,855
Total heat gain (BTU/h): 38,744
Total heat loss (BTU/h): 63,982

And with "Excellent" construction methods and very little air infiltration:

Square feet (whole house): 4868
Sensible heat gain (BTU/h): 22,589
Latent heat gain (BTU/h): 5,078
Total heat gain (BTU/h): 27,667
Total heat loss (BTU/h): 44,475

This is without any "cushion" or "safety" factor... just the raw numbers. I also did not account for any window shading, but I did use the real world indoor air temps that the family is always re-adjusting the thermostat to in our current home. I also haven't added any additional forced outside ventilation.

I know we're building with a very tight envelope (ICF foundation with a south-facing walkout, timber frame house with an external insulation system), but 2.5 to 3 tons of cooling seems a bit light compared to the estimates that we received. One of them was based on 1 ton/900ft^2, (5.5 tons by my count... he quoted 9 tons total water-source DX units). The other was for 7 tons. Others never submitted their quotes.

Your numbers indicate that .5 ton of central dehumidification using the ventilation ducts (DOAS) plus floor radiators for the sensible load (say 2 more tons) should work. With geo and the large radiators, it is very efficient. If your geo HP is 3 or 4 tons (oversized for summer), no problem, it won't effect humidity levels like an oversized air based AC might.

I don't know, but I suspect that commercial HVAC engineers don't make so many "off by 100%" errors.

thanks for the feedback jonr.

Based on these numbers, what total cooling capacity should I be looking for, or how much "padding" do I want to add? For sure I can't see where I will need 7 or 9 tons that were quoted. That's how I ended up pursuing this myself (until I started seeing these quotes, I was too busy/too lazy to do the necessary ciphering).

Here was my original plan with WTW geo:

Heating cycle:

Basement radiant slab
First floor radiant staple-up with diffuser plates
ERV installed in mechanical room to supply basement and first floor.
Second floor: hot water supplied to 2 each air handlers with ducted outside air exchange (1 for each 2nd floor wing as the great room vaulted ceiling splits the upstairs)

Cooling cycle:

Basement and first floor cooled via hydronic AHU and metal ducts (all inside the conditioned space)
ERV maintain air changes
Second floor: cooling water supplied to above mentioned 2nd floor air handlers

What changes to this would you recommend for maximum comfort and efficiency?

Thanks again for helping to create another more educated consumer!