Hello All. We live in the southern part of mexico and just bought an old 15 room hostel and we are planning to renovate it. The construction has pure rock walls about a foot thick and the sun mainly hits the concrete roofs and barely any of the exterior walls. The rooms are not hot inside, even at mid afternoon 40c heat, but since most guest would be people from US, Canada they would expect A/C. If you want to see the place so that you can better visualize it, here is the link to one of the online adds from when it was for sell. http://www.realestateyucatan.com/eng_standard.php?listing=2122&offered=sale The place sits on a 33ft/10mt by 165 ft/50 mt lot The first 36 feet/10 mt is/are fully constructed with two 14ft x 14ft rooms (4mt x 4 mt) on each side and a 4ft x 35ft ( 1.5 mt x 10.6 mt) hallway. the The four rooms are as follows: Right side is Office and Bedroom 1, Left side are two connecting rooms for dining. After those four rooms are all the hostel bedrooms (with the exception of room #1) There are 14 rooms out back and 1 Kitchen and a 4ft wide pathway down the middle. Ten of the 14 rooms are less than 150 sq ft and the two largest are just under 300 sq ft, that leaves 3 (#1 as mentioned as 190 and two others of 165sq ft.) Currently the place has Two 220v services (each side has it own 220v service/meter) We are wanting to put small A/C units (mini splits) in each of the bedrooms and in our office. Because of that we are considering add four new 220v services and using them just for the A/C units. Here is the reason I messaged you.

1. Does our idea sound right?
2. Would you be able to suggest wire gauge?
3. Considering the distance to the last rooms how would it impact the load on the wiring?
4. If 110v 7500 BTU mini splits will cool the rooms would that be best or would it be better to pay the extra for 220v 12,000 BTU units? I know the 12,000 BTU's would use more watts, that is why I was thinking of the 7,500 BTU units.





Thanks alot


Joe Gomez

Pepomx, Yesterday at 8:58 AM
Reply

 

Electrically I see you using up to 20 12,000 BTU units which each would draw about 6 - 8 amps on 230 volt power giving a total power draw for AC of around 120 - 160 amps. Around here that would run off of a normal 200 amp service without problems so I don't see the reason for needing 6 services for a single building of your size unless you have some odd regulation that does not allow you to have normal modern sized electrical services.

If it was me I would be putting the bigger AC units in the larger rooms and smaller ones in the littler rooms and running the whole place from a new single point centrally located 400 amp service. Wiring wise 14 ga would be good for 15 amps and 12 ga would be good for 20 amps circuits.

Consult your local codes for details.

 

Thermally, I see you using about 9 tons of air conditioning, but I don't have a squirrels clue about concrete roofs in Yucatan. Anyway, in Florida, we rule of thumb: 500 square feet per 12,000 B.T.U.s Throwing a ton into 165 square feet seems absurd. I would suggest something like a Daiken single condensor with tiny blowers in each room, but the efficiency of that depends on occupancy. You need a real air conditioning person familiar with the territory.

 

""The rooms are not hot inside, even at mid afternoon 40c heat, but since most guest would be people from US, Canada they would expect A/C."" { Spoiled much ?? }

What is the average level of humidity ?? Is there a prevailing breeze, or a lot of dead-air time ?

This sounds as though if you kept the air moving with a small fan, or ran small dehumidifiers, the AC a/w/a the extra electric service, would be an overkill, and use more power than necessary...

My 2 cents

 

Hello All. We live in the southern part of mexico and just bought an old 15 room hostel and we are planning to renovate it. The construction has pure rock walls about a foot thick and the sun mainly hits the concrete roofs and barely any of the exterior walls. The rooms are not hot inside, even at mid afternoon 40c heat, but since most guest would be people from US, Canada they would expect A/C. If you want to see the place so that you can better visualize it, here is the link to one of the online adds from when it was for sell. http://www.realestateyucatan.com/eng_standard.php?listing=2122&offered=sale The place sits on a 33ft/10mt by 165 ft/50 mt lot The first 36 feet/10 mt is/are fully constructed with two 14ft x 14ft rooms (4mt x 4 mt) on each side and a 4ft x 35ft ( 1.5 mt x 10.6 mt) hallway. the The four rooms are as follows: Right side is Office and Bedroom 1, Left side are two connecting rooms for dining. After those four rooms are all the hostel bedrooms (with the exception of room #1) There are 14 rooms out back and 1 Kitchen and a 4ft wide pathway down the middle. Ten of the 14 rooms are less than 150 sq ft and the two largest are just under 300 sq ft, that leaves 3 (#1 as mentioned as 190 and two others of 165sq ft.) Currently the place has Two 220v services (each side has it own 220v service/meter) We are wanting to put small A/C units (mini splits) in each of the bedrooms and in our office. Because of that we are considering add four new 220v services and using them just for the A/C units. Here is the reason I messaged you.

1. Does our idea sound right?
2. Would you be able to suggest wire gauge?
3. Considering the distance to the last rooms how would it impact the load on the wiring?
4. If 110v 7500 BTU mini splits will cool the rooms would that be best or would it be better to pay the extra for 220v 12,000 BTU units? I know the 12,000 BTU's would use more watts, that is why I was thinking of the 7,500 BTU units.





Thanks alot


Joe Gomez

Pepomx, Yesterday at 8:58 AM
Reply

Joe, as #12 implied in his answer, roof insulation is key to efficient AC cooling. You may want to check on that before you start your purchases/installations.

 

There is a huge amount of, "I don't know" right now. Florida houses with hollow concrete blocks 8 inches thick have a time constant of 9 hours. A solid rock wall a foot think might be an advantage if the nights are cool! How thick is the roofing concrete? Is is modified with substances to make it lighter? They tend to increase the insulation qualities. PackRatKing had several good ideas. Without good answers describing the climate and building materials, this conversation is stalled. From the information in the first post, I think no more useful information will arrive here. Is The Yucatan completely devoid of competent heating/cooling designers?

 

Thermally, I see you using about 9 tons of air conditioning, but I don't have a squirrels clue about concrete roofs in Yucatan. Anyway, in Florida, we rule of thumb: 500 square feet per 12,000 B.T.U.s Throwing a ton into 165 square feet seems absurd.

I'm curious as to how the general formulas take into account that sort of construction with high mass high density building materials.

I know with my old house I'm at the other end where the standard formula is way off and I have 5 tons of cooling capacity to keep things tolerable where the formulas say I should only need 2 - 2.5 of which the house originally had and it was dismally under powered.

 

I'm curious as to how the general formulas take into account that sort of construction with high mass high density building materials.

So am I, but the 6 months of courses I took to pass the State test had bloody nothing about high mass structures. I'm lucky that I even picked up the 9 hour time constant in the decades I was in the business.

You? Air conditioning? North Dakota? You have ground water at 7 degrees C. Just pump some into a radiator and blow a fan across it.

 

Contrary to what most believe we get miserably hot and humid points on our summers as well that more than justify having air conditioning.

And yes ideally I could pump well water through a heat exchanger and get a fair degree of cooling that way being my well water is about 40 -45 degrees on average year round coming from 180 feet down.

Believe me I have thought about setting up my own drilling rig and putting a number of thermal wells in for the new house.
Given what the greedy drillers who do that here now want per foot I can go out and buy a good used 2 ton truck and build my own rig and still come out money ahead.

$4000 to drill one 200 foot hole in the ground and stick $500 worth of PVC pipe in it are they nuts?

 

Contrary to what most believe we get miserably hot and humid points on our summers as well that more than justify having air conditioning.

And yes ideally I could pump well water through a heat exchanger and get a fair degree of cooling that way being my well water is about 40 -45 degrees on average year round coming from 180 feet down.

Believe me I have thought about setting up my own drilling rig and putting a number of thermal wells in for the new house.
Given what the greedy drillers who do that here now want per foot I can go out and buy a good used 2 ton truck and build my own rig and still come out money ahead.

$4000 to drill one 200 foot hole in the ground and stick $500 worth of PVC pipe in it are they nuts?

Wouldn't you also need to apply for a very special permit to do that? Down here water's too valuable and is rigidly controlled by the government. One could easily land in jail or receive a very hefty fine for such a stunt.

 

Wake up, Martinez. We just had a conversation about the lack of government interference in the Badlands of North Dakota. Besides, what's the harm in pumping water up, warming it 5C degrees, and putting it back in the same strata a few hundred feet away from the first hole?

As for drilling my own? My criteria is, if I can buy the tools for less than somebody else want me to pay them, I can do the job cheaper, myself, and still own the tools. Go tcm!

 

Wake up, Martinez....

I've been trying to do that all day... but the heat (37°C, 99°C) coupled with the high humidity have kept me in a dreamlike stupor... it's like a warm hibernation while awake...

 

$4000 to drill one 200 foot hole in the ground and stick $500 worth of PVC pipe in it are they nuts?

At that price, I should charge $52.50 for the 3 foot hole it requires to put in a fence post! Which is still on my "to do" list, as soon as the water table is down 3 feet.

At least it's down enough today that I could park my new (2006) car on the back porch without sinking into the sod. I know, 2006 isn't, "new" but it doesn't rain on the inside, it has a new transmission, and I paid $7000 lower than its trade in value.

I can fix the turn signals, the electric window motor, and re-upholster the drivers seat for way less than $7000!

 

I've been trying to do that all day... but the heat (37°C, 99°F) coupled with the high humidity have kept me in a dreamlike stupor... it's like a warm hibernation while awake... View attachment 89917

Go visit tcmtech. Place your warm Mexican butt on the ground, and you will be shivering in 15 minutes.

 

Go visit tcmtech. Place your warm Mexican butt on the ground, and you will be shivering in 15 minutes.

I'd probably first dig my overheated mexican-ostrich head in the ground before even thinking of my butt...

 

Wouldn't you also need to apply for a very special permit to do that? Down here water's too valuable and is rigidly controlled by the government. One could easily land in jail or receive a very hefty fine for such a stunt.

No water issues here. In fact I just set up two 2" pumps to pump water from our stream into my brothers duck pond to bring it up some more and the second one to his garden to water the corn.

As for subsurface water that too is largely unregulated around here. We have more than enough, average water tables are too high in most places now, so no one cares if anyone uses more.

Around her no one cares about what a person does so long as the smoke cloud cant be seen from more than 3 counties away. Anything bigger than that and we have to notify the local fire departments ahead of time so they know its on purpose.

 

I'd probably first dig my overheated mexican-ostrich head in the ground before even thinking of my butt...

I had to dig in a new water hydrant over at my dads place a few weeks ago with my backhoe. At ~ 7 feet down the ground was uncomfortably cold.

 

I had to dig in a new water hydrant over at my dads place a few weeks ago with my backhoe. At ~ 7 feet down the ground was uncomfortably cold.

I would suggest a horizontal water loop, closed system, but I assume you know how and whether it's the right choice, compared to a vertical system, open loop.

 

Horizontal or vertical both work well here but for me I live on the side of a hill which makes putting in a lot of horizontal lines a bit more work plus it would tear up a huge amount of my yard as well. I have the machines to do it and the cost per foot doing it myself is pretty cheap though so I have been considering it for some time as a viable option for the new house some day.

The biggest problem is I don't do things half way though so if I am going to put in a ground source heat pump system its going to be big enough to do the primary heating and cooling for the new house, old house, shop and whatever other buildings I may add to it someday being the hot water heat systems are already in place so setting that up to also work as a central cooling system for multiple buildings is not that much of a change.

Mostly its just because I just have a good used 10 - 12 ton commercial heat pump unit with matching liquid to liquid heat exchangers and circulator pumps sitting around doing nothing.

 

There is a huge amount of, "I don't know" right now. Florida houses with hollow concrete blocks 8 inches thick have a time constant of 9 hours. A solid rock wall a foot think might be an advantage if the nights are cool! How thick is the roofing concrete? Is is modified with substances to make it lighter? They tend to increase the insulation qualities. PackRatKing had several good ideas. Without good answers describing the climate and building materials, this conversation is stalled. From the information in the first post, I think no more useful information will arrive here. Is The Yucatan completely devoid of competent heating/cooling designers?

The roof is a 3 inch slab sitting on steel beams. But the rooms are actually fresh now. The never really get hot. I was just wondering if 110v 3/4 would be better than 220v 1 ton. On a website I plugged in the variables and half the rooms showed as needing about 6000 BTU's only.