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I purchased a 60 x 100 insulated metal building. It had 3…

I purchased a 60 x...
I purchased a 60 x 100 insulated metal building. It had 3 1991 7.5 ton gas packs in it using lp tanks. The tanks are gone and they stole the guts out of the 1991 units. I'm building living quarters on the inside of the building of about 1,500 square feet. I will probably be putting a 2 1/2 or 3 ton heat pump for that part. The eave height of the building is 12 feet. I'm left with with 4,500 sq ft of building to heat and cool. I'm assuming I will need to go back with 2 7.5 ton units and heat strips. Is there anything smarter I can do than that? I'm assuming electric is going to be out of sight, not to mention having to pull bigger wire there.
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Customer reply replied 1 year ago
The building only has one 10 ft roll up door and two 3 foot man doors. I will be wiring race cars which will average staying in the building for two weeks at the time so there will not be a lot of traffic in and out. No engines running and only two people working. I will have an air compressor, 3 computers, and probably a refrigerator.
Customer reply replied 1 year ago
The climate is mild. Sanford, NC
Answered in 1 hour by:
7/17/2017
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,798
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified

Hello

I am a retired mechanical engineer and HVAC/ electrical/ refrigeration and boiler contractor ... with 56 years in this business. The last 20 of those years consulting for major firms nationally.

Heat pumps will work well in that climate.

If you want applications engineering on that I will submit a $50 premium services offer.

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Customer reply replied 1 year ago
Ok, I will pay that for some good advice.

After you accept I need some pictures of how the existing 7.5 ton units are mounted on the roof, and the Brand and model number.

We can go from there

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I also need to know the ceiling height, and how far it is from the ceiling to the underside of the roof.

Some photo's of that will be useful also.

You can use the 'add files' link to get those photo's to me

Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,798
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
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Customer reply replied 1 year ago
There is no ceiling in almost all of the building other than two small offices and a bathroom constructed from Sheetrock and stud walls at standard 8 foot height and it's open above them. The living quarters I build will also be Sheetrock and stud walls at 8 feet and will subtract almost 1,500 sq feet. It's a standard Ceco a roof metal building with steel framework and a brick facade on the front. The eave height is 12 feet and the roof is 1 on 12. The insulation is just the white plastic stuff. The original units installed in 1991 were 3 units, all 7.5 tons. They had 70 employees and 70 electric sewing machines running with no problems cooling the building. All three units were ground level dividing the building in thirds on the 100 foot level no side. The return for each was ground level also within 2 feet of the unit on the inside with basically no duct work. The supply turned up and went to the ceiling as soon as it came inside the building and I did see evidence that they had a duct sweating issue at the transition that turns the supply upward. I'm not planning on keeping the units in the same place. I'm not sure if I will go with package or split units but thought of mounting them on some framework near the top of the building on the outside and the building penetration would be made near the top of the building so it will be even with the duct work or air handler. I will most likely replace all the duct work. I will go by and take picture in an hour.
Customer reply replied 1 year ago
I've tried many times to upload files in the past but it has never worked. I hoped with the new design of the site, it would have worked but it still doesn't. https://drive.google.com/open?id=0B5OrVoapMVPTSDhVNGVqdGQ0Ync

Thanks, ***** ***** the pictures. We can discuss all of the options and various configurations in detail.

.

The roof is sufficiently built to put the split system heat pump units on, that will put them out of harms way, accessible for service, and with short refrigerant piping to the air handlers hung from the ridge beam. That would be your lowest installed cost... and least duct work required.

All other options will cost more except just replacing the existing units on the ground and modifying that duct work to suit new packaged heat pumps.

The cooling capacity required per working person is 500 btu/hr per person, with 70 people it took 3 tons of AC just to cool the people. Tell me what the peak occupancy will be when the building is in operation.

A sketch of the floor plan will be very useful, especially showing any partitions and the peak occupancy of any partitioned areas.

Figure 3 tons of cooling for the 1400 sq ft living quarters if you want to hold 72F-75F inside air temperature on 100F days. 2.5 tons would work suitably well on all other days. I like to oversize heat pumps slightly so that I maximize the heat pumps heating capability on cold days

-------------------

With heat pumps, back up heat is required. Heat pumps are only efficient to 20F outside air temperature, below that auxilliary heat is required.

If the space is open, one large gas fired resnor heater would keep an open space area livable and be the least expensive of alternatives...

If the space will be heavily partitioned we will need to take a different approach... possibly electric resistance back up heat for each zone.

We can toss this around extensively.

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A note on electric resistance back up heat.

The utility companies in most areas have what is called a 'demand charge'...so that the highest 15 minute peak usage in any given 3 month period, sets a premium demand charge for the entire 3 months.

.

For instance one very cold day when electric resistance heat peaked for just 15 minutes, your entire bill for the next 3 months would have 30 to 60% demand charge in addition the power you used that month.

This is why I am recommending a Reznor gas fired back up heater if you have one large open space.

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Customer reply replied 1 year ago
The occupancy would be 5 people. It's possible a group of customers may come in for a few minutes or possibly a party or something once a year but not as a normal thing. I was thinking of possibly building a framework to set the units on up at ductwork height(probably 10 feet) and then just going straight into the building as they do now. I have no problem with splits though other than running more wire to them. The old pumps had gas to them but I was thinking of using heat strips instead. What are your recommendations?
Customer reply replied 1 year ago
I missed the message about the heaters. It's pretty open. Let me look and see what kind of heater that is.
Customer reply replied 1 year ago
I see the reznor. Those units sure do heat. I'm ok with that idea. The areas are mostly open. Would I put in one large unit or multiples? If I put in a large one, how many but/h would you suggest? And will the heat pump be able to bring them on automatically?
Customer reply replied 1 year ago
If either of the two 7.5 ton units were allowed to turn on the reznor, it doesn't seem to me like it would make much difference on its placement with all the air circulating or am I thinking about that the wrong way?

Hello again, one each 250,000 btu reznor heater will be sufficient....it would be set to fire whenever the building got below its set temperature. 70F or so... the heat pumps would be wired to run their blowers whenever they were in heating or cooling mode, and whenever the reznor heat turned on.

.

Two 7.5 ton packaged SEER 14 efficiency heat pumps will work for the open area.... you could get by nicely 90% of the time when it was less than 90F outside with two 5 ton heat pumps....it might warm up to 80F inside on a 105F day with the 5 ton heat pumps.

One 3 ton heat pump with 20KW of electric back up heat will work for the residence.

Send me a top view photo of one of the 7.5 ton units, so that I can see the supply and return duct connections..I will select an optimal set of packaged heat pumps for you.

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Customer reply replied 1 year ago
I just got this from my friend at my power company but not sure if it makes a difference or not:: I haven't heard anything at all about this with CEMC. Now Duke may be a different story. I know we haven't used load management or peak times in years, even before I started there almost 11 yrs ago. I will ask about this and let you know what they say. I did see someone post this the other day that lives in Benson. They thought their AC unit froze up and then found out this is what happened...
Customer reply replied 1 year ago
Would it not be more beneficial to me to use the reznor just like the heat strips on the units where it only came on when the heat pumps couldn't keep up?

You need the heat pumps blowers to move the reznor heat around at floor level, lacking that the ceiling will very hot and floor level a bit cool.

OR you can use 2 Reznors and point them 30 degrees toward the floor.... to get a swirl effect of hot air onto the floor, its more even heat though to let the heat pump blowers to move the air around. either way is generally at least workable.

------------

GoodmanMFG.com one of the nations largest and most price competitive makers of AC equipment in the US was bought out by Daikin in Japan... now the residential line of AC equipment carries the Goodman brand and their heavier commercial systems, still made in the USA, carry the Daikin brand. Daikin equipment is on the high priced, high quality end of the spectrum.

Their 7.5 ton packaged heat pump should be as good or better than any and probably at close to the lowest price... with luck you will be able to buy it directly from www.DAIKINac.com

click here

This may not be my final recommendation, I need to look into the other options a bit more

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Demand charges:

One of my clients in the SF bay area before I retired retained me to sort out ways of reducing his electric utility costs, looking at his bills of around $2500 a month, I could find no demand charges...I called the utility, the people I spoke with there had never heard of a demand charge. (that is like a bartender having never heard of beer)

But his bill had a line item called 'factor'... and listed it as just 40 ... not 40% or 40KWH, just 40

Doing the math on his bills and stated KwH usage and listed charge per KwH.... the bill was 40% higher than that amount.

It was a hidden demand charge of 40% based on his 15 minute peak during the previous 3 months.

The utility hid the charge by labeling it merely as 'factor' no units, no percentage, as I recall not even a dollar amount on the factor line.

They just added it in to the total without showing the dollar amount explicitly...

click here for one of several articles on the hidden demand charge.

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Customer reply replied 1 year ago
Ok, I think I have what I need. I've had my refrigeration cards for years and could possibly buy from a local dealer but their prices are sky high. I don't mind ordering from the internet. Where is a good place to buy from?
Customer reply replied 1 year ago
I just talked with the previous owner of the building. He said the building specs called for 3 units 5 tons each but he made them put 3 units of 7.5 tons in. He said even with the 70 employees, there was never a day that the building wouldn't cool down.

Hello again, the rule of thumb for your climate with the occupancy you have is 500 sq ft of floor space per ton, so at 6,000 sq feet that is 12 tons total. 3 ea 5 ton units will do you very well unless its gets to 105F outside, in the late afternoon, then you might get up to 78F inside for a few hours.

click here for Goodman online sales direct

You will be best off with 3 phase equipment. verify the voltage and phase for me please, I will see what I can find for you in a 3 phase or single phase depending on what you have on site.

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Customer reply replied 1 year ago
The living quarters inside the building will be between 1,200 and 1,400 once the design is complete I think. That would leave between 4,600 to 4,800 left for the building. That would seem to be between 9.2 to 9.6 tons using your 500 number. Daikin makes 6 ton 3 phase units I found online significantly less expensive than their 7.5 ton units. For the living quarters, because I will be heavily insulating for soundproofing and the fact that it is inside the building, I think I would want to go with a 2.5 ton high efficiency unit. I am unable to find a goodman 2.5 ton, 230 v three phase unit available for purchase unless it's special order. The prices I found online were with AC wholesalers and Budget Heating & Air conditioning. The goodman online sales only offered me 16 seer, 2 to 5 tons but didn't offer prices.
Customer reply replied 1 year ago
I ordered the units

You are on the right track, just be sure the voltage is the same.

Send me a link on the 6 ton units please, are they heat pumps?

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Customer reply replied 1 year ago
http://www.budgetheating.com/2-5-Goodman-16-seer-heat-pump-package-GPH1630H41-p/196024.htmhttp://www.budgetheating.com/6-ton-Daikin-Package-Unit-central-heat-pump-system-p/172053.htmYou've been plenty of help so I'm ready to accept. I also would like to know how to size gpm for a tankless electric water heater. 1,400 sq ft with one shower(high flow shower head), 2 bathrooms, one kitchen. And if you think they are a good idea vs a conventional water heater. I can ask it in a new question if needed.

Hello againm there are several issues:

1. Shop those prices, the 2.5 t ton unit is not low at ~$2500.. The 6 ton is probably only slightly high at $3,400.

2. With the apartment built in, you still have the heat load from the roof of the building over the apartment...... so your two 6 ton units should work very well up to 95F outside, then it might warm up 3 or 4 degrees F above your set point in the afternoon on those few days a year.

Leave that spare 7.5 ton ductwork in place so that you can add another 4 or 5 tons later.

----------------

Regarding the water heater, I am biased, I like a 30 gallon tank type electric water heater in your application, it will run for 10 years without trouble, the tankkess gas fired are high maintenance items

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Customer reply replied 1 year ago
Ok, I was referring to tankless electric, not gas. My uncle bought one and said it was great for him but it's still new. I was just trying to save on future electric costs since we would only use minimal hot water. Two showers a day and hand washing.

tankless electric is better than tankless gas.... its a bit of a toss up.

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Customer reply replied 1 year ago
I forgot to accept the answer but I will do it now. I am about to submit another question pertaining to fire code and living inside a commercial property. If you have knowledge of this I will submit the question directly to you. If not, I will submit it open.

Submit it open. However that answer will be dependent on your local building codes... those codes are sometimes not enforced....generally you can live in a commercial property however. The problems revolve around doing business from a residential zoned property, even that is not often enforced with so many people working from home.

There would be a problem if you wanted to raise hogs at your home though... you could however live on a ranch or above a restaurant you own, that is completely common.

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