Any HVAC Guys Here?

[BHarrison]

Thanks on the GPM rule of thumb! WOW, that's alot of water! I would think there would be a "temp split" rule of thumb rather than a GPM rule of thumb since incoming water temperature is a variable.

I am guessing the unit is at least 10 years old. What should I run through it to clean it?

Unfortunately, it does not have a sight glass. I wish it did, it would cut-out alot of guess work.

As for the domestic hot water exchanger, I was thinking about that. The high pressure line comes out of the compressor, and goes directly into the domestic hot water exchanger. This line goes in HOT, and comes out luke warm. Does this aid in the air cooling (evap coil) process, or is it a detriment?

Thanks

 

[RickM]

Ben,
Yes there are rules of thumb for temperature differential as well. For the water side expect about 10 - 12 degrees. For the air side at 'standard' conditions expect 15 - 20 degrees across the coil. If humidity is high then the difference will be lower. Remember though 'rules of thumb' don't apply to all situations.

Cleaning the water side of the heat exchanger is fairly easy. The chemical approach using a tub and a <font color=green>DILUTE</font color=green> acid and recirculating pump works well. You are wanting to dissolve the lime/calcium scale. Products for lime removal are available at most plumbing stores. The trick is to give it time to work. Plan on circulating for 30 minutes or more if needed. You will have to keep adding the acid every so often because the acid gets neutralized as it dissolves the scale. You will know you are done when there is no more foaming.

The hot gas line going to the de-superheater should be well insulated both going and coming. In cooling mode you effectively get free hot water, but in heating mode you don't. That is because the btu's you just put into the hot water tank are now not available for space heating. Many times there is an option in the unit to bypass domestic hot water production. The other way would be to just raise the thermostat setting on the water heaters so they make their own. That way there would be no 'demand' on the de-superheater.

Are you planning to fully air-condition and heat your shop or is one mode more necessary than the other? Keep us posted.

 

[BHarrison]

Thanks Rick.
What your saying about the de-superheater robbing the heat in "heat" mode makes sense. I was thinking that was the case, but wanted a second opinion.

I live in Louisiana, so cooling is much more important than heating. We get a couple months of cold weather, and I was looking at buying a natural gas shop heater. Since the gas shop heater could coust +/- $500.00, I thought I should explore whether or not the heap pump could heat the shop. The area to condition is 1200 square foot with 12' - 14' ceiling. The unit (functioning properly) should be more than adequate.
Did you say 51,000 btu was 5 tons?

 

[MJB]

There are 12000 BTUs to the ton. Therefore 60000 BTUs would be 5 tons.

 

[Bob_in_Ma]

Them sure are some HEAVY air conditioning doohickies.

 

[frank_f15]

sorry so late getting back on this thread, but if u are sure it is not a water problem, have u put a set of gauges on the unit, to check the pressures?also remember 12000 btu= 1 ton but in all actually figure 10,000 practical, for loss of efficency.

 

[BHarrison]

I have put the guages on it, and come up with:

Low = 60 psi
High = 150 psi.

Does that sound right? Seems like high should be higher than 150. Also, Should the pressures read the same in cool, and heat?

 

[RickM]

Ben,
Glad to see you are sticking with it. I'm assuming you are in cooling mode so the low side pressure looks ok, but the high side is a bit low. Expect 60 - 70 psi low side and 200 - 250 psi high side if the refrigerant charge is correct. We need more info to diagnose further. Specifically the mode of operation, the inlet and outlet water temps, superheat and subcooling. To figure superheat we need to know the actual temperature of the copper line at the outlet of the coil (or at the compressor return), and for subcooling we need to know the actual temperature of the copper line just after leaving the heat exchanger. Converting the pressure readings to temperature, and comparing to measured line temps yields each result. Getting an acurate line reading is difficult without proper tools /w3tcompact/icons/frown.gif, but a cheap digital thermometer strapped to the line with insulation will work. Tell us what you find.

 

[BHarrison]

Ok, now we're talking.

Those readings I gave were in heat mode.

From now on, I will turn off the pump for the de-superheater when using the unit in heat mode. I disabled my de-superheater pump on my home unit, and saw a nice rise in air temp. (I'll hook it back up when the weather warms up)

I have a Fluke dual temp thermometer with A -B. That should do fine for getting water temps. It may be a couple days before I get some readings, but I'll get them, and post the results.

THANKS