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Spence

Joined on April 16, 2013

Last Post on July 27, 2014

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Equipment Matching

@ May 6, 2014 7:52 AM in 2.5 Condensor with a 5 ton coil

First check AHRI to see if your OD unit and ID coil have been certified. If not you may have a humidity issue. Then compare the SH and LH capacities of your OD unit at your design DB and WB (not AHRI conditions; yours!) to your load requirements. Remember, you can take "credit" for half of your excess latent should you have any to apply to your sensible, which always allows for smaller OD units if yoi can neutralize both loads.

CFM

@ May 6, 2014 7:31 AM in figuring CFM required

This is a wonderful practice; one of which our industry should have more followers. However, it tells you what you have yet doesn't address what you need (load). With these two bits together, we learn how closely the CFM required by the load and the field conditions (as your point states) can meet. The more narrow that gap is means everything to the occupants and the equipment.

Delta T

@ May 5, 2014 7:47 AM in figuring CFM required

Your temperature drop is based on the sensible heat ratio from your load calculation. A high SHR allows for a warmer coil, while a low SHR is the opposite. Once you have the CFM value, you have to determine if your blower can meet this requirement at an acceptable ESP using the performance chart from your unit.

Laundry Return

@ April 30, 2014 6:56 AM in HVAC Duct System

Since you haven't mentioned ducts, you may be describing a ceiling return plenum. This brings up a host of code issues if not installed correctly. This I assume, a you mention a second blower at the grille. Enclosing a joist space for a return will only give you 150 CFM if you're lucky, and it will throw your building pressures out of sync.

Laundry

@ April 29, 2014 7:34 AM in HVAC Duct System

If there are no other returns, you may have all outdoor air as a return with the negative issues as explained above. You will need some OA to satisfy the code requirement for ventilation. Ask your local HVAC professional to help with OA amounts, load calculations (commercial) and duct sizing based on your loads and the capacity of your blower.

2 HPs

@ March 25, 2014 6:11 AM in two 2.5 ton heat pumps for one 5 ton heat pump

This is a horrible idea, an application nightmare, and a frivolous waste of money and resources. Twinning normally works the other way; one OD unit on two furnaces and one large evaporator.

We need to get your load squared away before looking at more equipment options, especially those that lead you farther and farther away from the comfort and economy for which you're looking.

Pikes Peak

@ March 21, 2014 6:27 AM in High efficiengy heat pump connected to a single stage blower

I have some real and deep concerns for you. Some regional "magic numbers" don't address your house, which, as do you, has it's own "personality." For example, just one 3' x 4' window of reasonable quality can raise your summer load by almost 500 BTUH. Tell me how magic numbers show house details! We need to do a proper load; I will be happy to run one for you. I will need a bucketload of info, so you can ping me directly if you want.

Don't fall for the R-22 trap, and NEVER use an existing coil, unless five years old or less and is an APPROVED match after a TXV swap!

Help Needed

@ March 20, 2014 12:07 PM in Help Needed

Looking for a plumber with NJ Public Works certification. DPMC a huge plus!

Sizing

@ March 19, 2014 9:00 AM in High efficiengy heat pump connected to a single stage blower

NEVER size a HP to heating! Your load should be one BTUH value based on weather station, building materials, glazing, insulation, doors, walls, roof, etc. What load calculation program are you using?

Heat Pump Sizing

@ March 18, 2014 7:23 PM in High efficiengy heat pump connected to a single stage blower

First of all, you need to size your heat pump for the cooling load, not heating. In the winter the HP has support from your oil furnace. You won't dehumidify in the summer sizing to your heat loss. You need a factory match with your ID and OD coils, as well as tubing. How did you end up with a huge cooling size (5-tons) if your heat loss is only 40,000 BTUH?

HP Savings

@ March 18, 2014 5:58 AM in High efficiengy heat pump connected to a single stage blower

On behalf of all of us, you are most welcome! What is the HSPF of your unit choice? Just landing on a SEER rating says nothing about heating. Then you have two balance points to consider; economic and thermal, so you can optimize the hidden benefits of your heat pump. You have a little work yet to do, and we will help you through it. This is the fun stuff!

2-stage Response

@ March 17, 2014 7:36 AM in High efficiengy heat pump connected to a single stage blower

No. The Y circuit is the compressor contactor. The comfort control simultaneously makes contact to the fan circuit (G). What you're missing (see earlier posts) is the two compressor signals from Y and Y2, or similar markings, such as Y1, YLO, etc. This control scheme has to be built in to achieve your certifications and ratings.

Electric

@ March 17, 2014 7:24 AM in Heat pump only, or combo?

Your electric costs are 4 times the national average? Something doesn't seem right.

Evergreen

@ March 15, 2014 10:24 PM in High efficiengy heat pump connected to a single stage blower

It's not the motor; it's the control system that stages speeds. The Evergreen does have speed taps, yet only one can be used at a time. It doesn't jump from tap to tap. You would have to have a variable speed ECM to do that.

Blower Speeds

@ March 15, 2014 10:19 PM in High efficiengy heat pump connected to a single stage blower

By default, the thermostat signal for compressor operation (Y) goes to the highest speed you have set. The heat pump is "stupid" as it doesn't know if it's heating or cooling; that's the reversing valve's job, so you get the same speed both summer and winter. Depending on when you're in restricted mode, your furnace will operate on the heating speed set by you or the factory setting if you haven't changed it.

Evergreen ECM

@ March 13, 2014 10:15 PM in High efficiengy heat pump connected to a single stage blower

Fantastic motor, yet not intended for 2-stage applications.

Y2

@ March 13, 2014 11:23 AM in High efficiengy heat pump connected to a single stage blower

This is your second stage cooling signal from the comfort control. There are a litany of reasons why you need an AHRI matched system; efficiency, performance, and comfort are just a few. Understand that when the CC calls for 2nd stage, the blower and outdoor fan ramp up to match the higher compressor output, so without this feature you have wasted a bucketload of cash in a two-stage HP that will never live up to expectations.

2-stage HP

@ March 11, 2014 4:19 PM in High efficiengy heat pump connected to a single stage blower

You're better off using a single stage heat pump with your existing furnace.

2-stage HP

@ March 8, 2014 6:24 PM in High efficiengy heat pump connected to a single stage blower

Can you connect to a single speed blower? Yes. Is it a good idea? No. You'll have to hook up Y2, losing the 1st stage and the benefits therein.

There is Nothing Wrong

@ March 3, 2014 1:29 PM in What's wrong with this?

It is the evaporator's job to convert liquid to gas.

Furnace Issues

@ March 3, 2014 1:25 PM in furnace problem

The first thing that is not right is the limit. Unless approved by the manufacturer, NEVER raise the cut-out temperature.

Dryness and comfort are independent issues. Check the thermostat reading against a high quality thermometer; the two should be within 3 degrees. Also check your TR and compare to the nameplate. The CFM numbers sound like the cooling dips, not the heating.

Check your RH with a psychrometer; 30% is the lowest on the comfort scale. If you don't have one, cut the tip off a clean white shoe lace, soak it in water, and slip it over the wand of your thermometer for a wet bulb value. You'll have to convert to RH. For example, 63 degrees WB is 50% RH.

The Evaporator

@ February 27, 2014 8:20 AM in Apologies!

Delivering comfort and economy is all about pressure, and how to manipulate it to your advantage. In the purest sense, the outlet of the blower is the highest pressure while the inlet is the lowest. Evaporator coils can easily be the system component with the highest PD, so you want to account for it where you have the most with which to work (blower outlet). The heat exchanger's PD is included in the blower selected by the manufacturer.

With this in mind, the furnace would have to be raised to get the coil directly underneath, and there are coils and accessory plates expressly for this purpose. Some have left the furnace in place and put the coil in the crawl (a horrible idea). Watch your RA though; raising the furnace for the coil can make changing filters a PIA.
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