High-SEER mini splits instead of WSHP?

slippy · 04-10-17, 01:30 PM

I've had problems with my well drilling. While I COULD get a fair amount of sustained flow by starting over and going with a 4" diameter casing (to get an ejector inside) or 6" diameter (for a submersible pump), I'd have to ignore several local and state regulations of which I was previously unaware.

I've also noticed that it seems like mini split heat pumps now offer EERs that absolutely rival what I thought I'd be able to do with water-source geothermal.

I'm shopping and looking, but figured there's got to be folks here that have already done all that legwork, who could perhaps save me some time, and save me from making some buying mistakes.

My total desired heating and cooling tonnage is 7. I have no real preference as to how this is broken up. Cost may largely dictate this, but I should be able to get decent airflow throughout the building (using the existing HVAC blowers if I must) with about any setup -- just a couple of units, or something like 10.

I haven't completely given up on going with a water-source heat pump (or adding a water-refrigerant heat exchanger in line with my existing ASHP). By the time I'd pay for the mini-splits, I might just be better off sticking with lower efficiency. BUT, I really need to be looking at all my options.

So, what are your mini-split thoughts and recommendations?

oil pan 4 · 04-10-17, 01:45 PM

Then the question is will you get caught?

I like decentralized mini splits. They are so cheap and efficient I don't think I would bother with a big complicated centralized system.
Seems like the ground water systems get a marginal efficiency boost over the high efficiency splits but come with a huge increase in cost and complexity.

MN Renovator · 04-10-17, 01:49 PM

7 tons? Is this a huge building like an office or other commercial setup? or do you have some other need for this much tonnage?

It sounds like it's your property if you are drilling the well but if it's regulations that you are worried about, things get harder when you do things in a higher visibility area like at a business.

slippy · 04-10-17, 02:07 PM

We have an existing 5T split system, and a 2T package unit (gas pack). This is at our building, which has 5000sf of area, in Charlotte NC. There's just a single SE-facing window, and a single NW-facing glass door. Our lighting is LED, and we're pretty energy-efficient. 7T MAY be overkill, though it is what we had, and on the hottest days, it is not always enough... though I doubt it is all running at optimal efficiency.

I do like the idea of having redundancy, vs. just a large point of failure (as well as the ability to "put the cool" where you need it.

As far as the well/permitting/whatever goes, I'm not too afraid of the boogeyman, but to drill the well we really need to drill, it'd cost $6K about. As far as shallow water goes, I have water at 22 feet; with the slightest draw-down, I'm below the height from which we can lift. My test well was 1-1/2". Now, do realize that a 5T unit would ideally like to have about 15GPM. My pump was struggling to deliver 2.5GPM, and could only do so for 5 minutes before running out of water (liftable water; about 25 to 27 feet of lift is all you can get.)

I don't know if y'all are familiar with standing water column WSHP installs, but you draw from, and return to, the same hole. You can bleed off some water as its temperature rises to draw in "fresh" water from the surrounding area. Maybe I am just way optimistic, but I think something like that could work well for us. It may not take care of ALL of the cooling/heating requirement, but, damn, I sure think it ought to go a long way towards it. Since we are IN WATER, I think the temperature migration through the soil wouldn't be all that bad. I just don't see how I'd be raising the earth temp to near 100 degrees, which is what the high air temps can get to. Seems worst-case, even with the 40' well (20' of water) I'd still be better off than going air-source. Do note that we have a huge gravel pack; I'm guessing our well bore is about 6"-8" diameter.

So, I'm weighing trying to make water-source work, against mini splits. Pumping all the water I'd need to flow has got to be costlier than running the condenser's fan; I guess the savings are found by taking some of the load off the compressor. I'm just afraid that, even if I got everything built out OK, maintenance would become a pain in the butt.

Ugh. Help.

jeff5may · 04-10-17, 11:07 PM

Sounds like you need to get acquainted with the various technologies a lot better before you go and make some costly mistakes. You live in a not-so-extreme climate zone, so either system type will work for you if it is executed correctly. I'll tell you this: if your main concern is low maintenance and low cost, a central ASHP system will win. Filter change every so often is easy and cheap. It doesn't hurt to go window shopping.

If you were in a climate zone dominated by heating, and the temperature dropped below freezing for extended amounts of time, the ground source unit would be the clear winner. That's pretty much where the air source units struggle; above maybe 45 degF, they do well up into the high 90's.

oil pan 4 · 04-11-17, 07:30 AM

I live in new Mexico and planot to install a little over 5 tons maybe even 6 in a 1200 square foot house.
We have 9,000 in the bed room and love it. I am for sure going to put an 18,000btu window unit and 220v A/C circuit for it this year put a 2 ton inverter split in the kitchen dining room ares and put a 1 ton split in the large south facing bed room maybe next year.

DEnd · 04-14-17, 12:36 AM

Considering you are above the 6 ton range you are starting to look at commercial equipment. Air source VRF equipment is going to beat ground source on a first cost basis, and the operational savings aren't going to ever make up for the first cost savings of air source.

My guess is that your comfort problem is due to humidity, and thus air leakage. So the place to start is with building envelope improvements. If I were you I think my first step would be to get in touch with either Energy Vanguard in Atlanta or Advanced Energy in Raleigh (Energy Vanguard is owned by Dr. Allison Bailes who writes for Green Building Advisor, but Advanced Energy is just a reputable). Either of those will be able to at least give you recommendations on who hire to help you meet your energy goals if they are unable to do what you need.

DEnd · 04-14-17, 01:38 AM

Quote:

Originally Posted by oil pan 4

I live in new Mexico and planot to install a little over 5 tons maybe even 6 in a 1200 square foot house.
We have 9,000 in the bed room and love it. I am for sure going to put an 18,000btu window unit and 220v A/C circuit for it this year put a 2 ton inverter split in the kitchen dining room ares and put a 1 ton split in the large south facing bed room maybe next year.

OMG why? That's literally 2 or more times as much cooling as what would go in a freezer that size. In a well built house your load should be between less than a ton and just over a ton.

With that much capacity you are going to short cycle your equipment, which for mini-splits means a high vampire load. You will also likely have poor humidity control, which is just as important in your dry climate as it is in my semi-humid climate.

slippy · 04-14-17, 12:29 PM

We have people constantly coming and going, so no doubt, infiltration is an issue.

Where in NC are you? Charlotte here. What would you think would be a good humidity percentage indoors in the summer? I think we are low-40s in general; I have some sensors on order, so I can better monitor and automate.

I'm also thinking about trying to get a lot more air into the offices when the nights are cool, though I am a little concerned about increasing the latent load, due to increasing humidity.

One of our AC units will ALWAYS have a very thin, solid stream of condensation coming out of the drain.

oil pan 4 · 04-14-17, 01:32 PM

Inverters don't short cycle.
I wasn't going to run all of them at once.
The idea is to leave the air conditioner off all day then turn it on and cool off the house fast in the afternoon.
In the past I have used air conditioners that should have cooled but didn't and ended up leaving them on all day.

04-10-17, 01:30 PM	#1
slippy Helper EcoRenovator Join Date: Feb 2017 Location: Charlotte NC USA Posts: 37 Thanks: 1 Thanked 3 Times in 3 Posts	High-SEER mini splits instead of WSHP? I've had problems with my well drilling. While I COULD get a fair amount of sustained flow by starting over and going with a 4" diameter casing (to get an ejector inside) or 6" diameter (for a submersible pump), I'd have to ignore several local and state regulations of which I was previously unaware. I've also noticed that it seems like mini split heat pumps now offer EERs that absolutely rival what I thought I'd be able to do with water-source geothermal. I'm shopping and looking, but figured there's got to be folks here that have already done all that legwork, who could perhaps save me some time, and save me from making some buying mistakes. My total desired heating and cooling tonnage is 7. I have no real preference as to how this is broken up. Cost may largely dictate this, but I should be able to get decent airflow throughout the building (using the existing HVAC blowers if I must) with about any setup -- just a couple of units, or something like 10. I haven't completely given up on going with a water-source heat pump (or adding a water-refrigerant heat exchanger in line with my existing ASHP). By the time I'd pay for the mini-splits, I might just be better off sticking with lower efficiency. BUT, I really need to be looking at all my options. So, what are your mini-split thoughts and recommendations?

04-10-17, 11:07 PM	#5
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Sounds like you need to get acquainted with the various technologies a lot better before you go and make some costly mistakes. You live in a not-so-extreme climate zone, so either system type will work for you if it is executed correctly. I'll tell you this: if your main concern is low maintenance and low cost, a central ASHP system will win. Filter change every so often is easy and cheap. It doesn't hurt to go window shopping. If you were in a climate zone dominated by heating, and the temperature dropped below freezing for extended amounts of time, the ground source unit would be the clear winner. That's pretty much where the air source units struggle; above maybe 45 degF, they do well up into the high 90's. Last edited by jeff5may; 04-11-17 at 06:59 AM..

04-14-17, 12:36 AM	#7
DEnd Apprentice EcoRenovator Join Date: Nov 2011 Location: NC Posts: 117 Thanks: 6 Thanked 27 Times in 25 Posts	Considering you are above the 6 ton range you are starting to look at commercial equipment. Air source VRF equipment is going to beat ground source on a first cost basis, and the operational savings aren't going to ever make up for the first cost savings of air source. My guess is that your comfort problem is due to humidity, and thus air leakage. So the place to start is with building envelope improvements. If I were you I think my first step would be to get in touch with either Energy Vanguard in Atlanta or Advanced Energy in Raleigh (Energy Vanguard is owned by Dr. Allison Bailes who writes for Green Building Advisor, but Advanced Energy is just a reputable). Either of those will be able to at least give you recommendations on who hire to help you meet your energy goals if they are unable to do what you need. Last edited by DEnd; 04-14-17 at 12:23 PM..

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04-10-17, 01:45 PM	#2
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	Then the question is will you get caught? I like decentralized mini splits. They are so cheap and efficient I don't think I would bother with a big complicated centralized system. Seems like the ground water systems get a marginal efficiency boost over the high efficiency splits but come with a huge increase in cost and complexity.

04-10-17, 01:49 PM	#3
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	7 tons? Is this a huge building like an office or other commercial setup? or do you have some other need for this much tonnage? It sounds like it's your property if you are drilling the well but if it's regulations that you are worried about, things get harder when you do things in a higher visibility area like at a business.

04-10-17, 02:07 PM	#4
slippy Helper EcoRenovator Join Date: Feb 2017 Location: Charlotte NC USA Posts: 37 Thanks: 1 Thanked 3 Times in 3 Posts	We have an existing 5T split system, and a 2T package unit (gas pack). This is at our building, which has 5000sf of area, in Charlotte NC. There's just a single SE-facing window, and a single NW-facing glass door. Our lighting is LED, and we're pretty energy-efficient. 7T MAY be overkill, though it is what we had, and on the hottest days, it is not always enough... though I doubt it is all running at optimal efficiency. I do like the idea of having redundancy, vs. just a large point of failure (as well as the ability to "put the cool" where you need it. As far as the well/permitting/whatever goes, I'm not too afraid of the boogeyman, but to drill the well we really need to drill, it'd cost $6K about. As far as shallow water goes, I have water at 22 feet; with the slightest draw-down, I'm below the height from which we can lift. My test well was 1-1/2". Now, do realize that a 5T unit would ideally like to have about 15GPM. My pump was struggling to deliver 2.5GPM, and could only do so for 5 minutes before running out of water (liftable water; about 25 to 27 feet of lift is all you can get.) I don't know if y'all are familiar with standing water column WSHP installs, but you draw from, and return to, the same hole. You can bleed off some water as its temperature rises to draw in "fresh" water from the surrounding area. Maybe I am just way optimistic, but I think something like that could work well for us. It may not take care of ALL of the cooling/heating requirement, but, damn, I sure think it ought to go a long way towards it. Since we are IN WATER, I think the temperature migration through the soil wouldn't be all that bad. I just don't see how I'd be raising the earth temp to near 100 degrees, which is what the high air temps can get to. Seems worst-case, even with the 40' well (20' of water) I'd still be better off than going air-source. Do note that we have a huge gravel pack; I'm guessing our well bore is about 6"-8" diameter. So, I'm weighing trying to make water-source work, against mini splits. Pumping all the water I'd need to flow has got to be costlier than running the condenser's fan; I guess the savings are found by taking some of the load off the compressor. I'm just afraid that, even if I got everything built out OK, maintenance would become a pain in the butt. Ugh. Help.

04-11-17, 07:30 AM	#6
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	I live in new Mexico and planot to install a little over 5 tons maybe even 6 in a 1200 square foot house. We have 9,000 in the bed room and love it. I am for sure going to put an 18,000btu window unit and 220v A/C circuit for it this year put a 2 ton inverter split in the kitchen dining room ares and put a 1 ton split in the large south facing bed room maybe next year.

04-14-17, 12:29 PM	#9
slippy Helper EcoRenovator Join Date: Feb 2017 Location: Charlotte NC USA Posts: 37 Thanks: 1 Thanked 3 Times in 3 Posts	We have people constantly coming and going, so no doubt, infiltration is an issue. Where in NC are you? Charlotte here. What would you think would be a good humidity percentage indoors in the summer? I think we are low-40s in general; I have some sensors on order, so I can better monitor and automate. I'm also thinking about trying to get a lot more air into the offices when the nights are cool, though I am a little concerned about increasing the latent load, due to increasing humidity. One of our AC units will ALWAYS have a very thin, solid stream of condensation coming out of the drain.

04-14-17, 01:32 PM	#10
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	Inverters don't short cycle. I wasn't going to run all of them at once. The idea is to leave the air conditioner off all day then turn it on and cool off the house fast in the afternoon. In the past I have used air conditioners that should have cooled but didn't and ended up leaving them on all day.