A technical question

A technical question.

Using R22 I want to know what is the idea range of head pressure to get the maximum heat out if the system with the least power input, IE the most efficient head pressure on heating.

Please no guesses, I do not want to run the system at 400 PSI and chew up heaps of power.

I have ways of controlling the suction pressure thus controlling the head pressure within some limits. The condenser (Outdoor coil) is somewhat oversized so that again allows me a range of suction pressures while the unit is running on heating. Both the heating and cooling modes have TX valves for refrigerant control and there is a receiver in the system.

No worries about low temperature IE freezing the outdoor coil as it does not get all that cold here.

As I said the main aim is to get a good heat result with a minimum of power usage.

So what PSI should I aim at from a design point of view on heating and economy?

Reply to
<ramrod
Loading thread data ...

maximum heat out if the system with the least power input, IE the most efficient head pressure on heating.

of power.

pressure within some limits. The condenser (Outdoor coil) is somewhat oversized so that again allows me a range of suction pressures while the unit is running on heating. Both the heating and cooling modes have TX valves for refrigerant control and there is a receiver in the system.

get all that cold here.

Wrong question. Ask 'How do I get the most efficient operation ?', as you did at first.

Answer : at the lowest input power level needed to exactly meet the current load, while running 24 / 7. Head pressure is only one part of that equation. Your head pressure will tend to be at the lowest point it can be to acheive that, but how you handle the fans, etc is all part of the picture.

And no, you don't run R22 at 400 PSI.

been involved in air conditioning for many decades, so am knowable on it. My design experience is mainly on straight cooling systems.

system that had 9 ton of refrigerant in it. Plus I commissioned a few plants that had 3,300 volt motors driving the compressors.

plant which had multiple large fan coil units and had 6 x Carrier 5H120 compressors on it all coupled together.

something like a 100-125 HP motor driving each of them and are an unloading 12 cylinder compressor.

condenser had balancing coils to take up any imbalance in the system, as any of the fan coils could heat or cool simultaneously if required as there were both heating and cooling coils in each fan coil unit.

Reply to
.p.jm.

Refrigerant pressures are only a very small part of the picture... once you have verified 400cfm airflow per ton in a correctly matched system, the correct way to charge a heat pump is using superheat, and subcooling according to the manufacturers specifications.... PERIOD.

what is the cold ambient and the SST in the coil??

Correctly sized, proper airflow, and charge correctly balanced.

Look at a couple of charging charts

Resi systems are not for the industrial hammer mechanic, its more like working on swiss watches by comparison.

Reply to
Steve

I know a lot of HVAC guys who can't work on refrigeration systems. ^_^

TDD

Reply to
The Daring Dufas

I am the designer and the manufacturer. It is a one off unit.

Balance charge has nothing to do with it as I said it has 2 TX valves and a receiver which takes care of the correct refrigerant charge in the coils. an extra couple of pounds of gas one way or the other makes no difference as long as there is enough gas in the system.

.> Resi systems are not for the industrial hammer mechanic, its more like

The average residential system is a simple install of a pre-made unit and does not require any design of the various components by the installer.

You simply stuff it in.

This a special design and all I am asking is what is the idea head pressure for heating on R22, so far I have not had that answer.

Reply to
<ramrod

I am fully aware of that still comes the question what is the best head pressure to get the most economical amount of heat from the system, that is all I am asking

That is what I said.

Reply to
<ramrod

I have met a lot of HVAC people who should not be allowed to work on HVAC systems, but I asked a simple question and it seems no on has the answer.

IE what is the best head pressure for the most economical operation in heating mode using R22.

I have worked on domestic fridges, domestic air conditioning systems, bar refrigeration systems (Temprites and bottle cabinets), commercial and industrial refrigeration and also huge systems like cascade systems with screw compressors, as well as commercial and industrial air conditioning systems.

Reply to
<ramrod

What is that you're doing with your system? Perhaps a little experimenting with data loggers for temperature and current draw including real time monitoring. If you can adjust your head and crankcase pressure, you may actually be able to determine your optimum settings by watching power used in relation to temperature and pressure. I happen to like TVX equipped systems myself even small ones because they're not too fussy about the amount of charge. I'm really curious as to what your application is?

I was figuring out a system for a two story house I was interested in where I could use a couple of semi-hermetic compressors with unloaders for capacity control to handle all cooling and refrigeration for the house. I wanted a small walk-in cooler/freezer too and my idea was to have a small rack system in a utility room that would use one refrigerant for everything. Alas I was unable to get the house but it was a fun mental exercise to find sources for all the parts and equipment.

TDD

Reply to
The Daring Dufas

Your not listening to what your being told. There is *NO* "best head pressure" for any specific refrigerant. the head pressure will vary depending on temperature and load. You say the system has TXVs on it... ok... charge the system by subcooling, and superheat.

You wouldn't be an EE by any chance, would you??

Reply to
Steve

have verified 400cfm airflow per ton in a

superheat, and subcooling according to the

THAT EXPLAINS IT ALL

receiver which takes care of the correct

the other makes no difference as long as

not require any design of the various

for heating on R22, so far I have not had

Reply to
Grumpy

A technical question.

Using R22 I want to know what is the idea range of head pressure to get the maximum heat out if the system with the least power input, IE the most efficient head pressure on heating.

Please no guesses, I do not want to run the system at 400 PSI and chew up heaps of power.

I have ways of controlling the suction pressure thus controlling the head pressure within some limits. The condenser (Outdoor coil) is somewhat oversized so that again allows me a range of suction pressures while the unit is running on heating. Both the heating and cooling modes have TX valves for refrigerant control and there is a receiver in the system.

No worries about low temperature IE freezing the outdoor coil as it does not get all that cold here.

As I said the main aim is to get a good heat result with a minimum of power usage.

So what PSI should I aim at from a design point of view on heating and economy?

Reply to
Grumpy

You cannot read, I am talking about head pressure, not the simple act of charging a system.

You have already shown your lack of knowledge by talking about a 'a balanced charge' in a system that has a receiver and TX valves.

You would not be a first year fridge mechanic's assistant would you?

Reply to
<ramrod

It explains why you stuck your nose in with no ability to answer the question.

Reply to
<ramrod

Grumpy raved

Seeing I owned my company and was in charge of the installations and commissioning they worked.

It is no surprise to see someone like you come in who cannot answer the question posed and then rave on, as obviously you have no knowledge of any value.

Reply to
<ramrod

Your ignorance is showing.... there is no "best" pressure... LLP, LLT, SP, ST, SH, and SC are dependent on ambient temps, and RH for both the condenser and evap..... especially with TXVs.

Your not going to have the same pressures and temps at 30F OD ambient as what you would have at 60F OD ambient. Maybe you should do a little homework on refrigerant pressure/temperature relationships.

Reply to
Steve

In a rough general terms.

The it is a ducted system covers 3 rooms, each room has a thermostat which besides controlling heating and cooling, it also opens and closes a damper to that room, so if a room is not turned on, then there is no air conditioning going into that room. This is for economy.

Pressure switches control the outdoor fans to control the suction pressure on heating to control the head pressure somewhat.

Additional pressure switches will turn on one of the other areas if the head pressure gets too high on heating. or if the suction pressure gets too low on cooling, as the air quantity will vary somewhat depending on how many rooms are turned on.

The outdoor fans are electronically controlled (Speed) while the plant is on cooling controlling the head pressure. I like to keep the discharge pressure fairly low, but high enough for the TX valves.

Yes, setting the system up with loggers would be OK but I was trying to get an idea of what head pressure I should be looking at as a starter in heating.

At the moment I am considering around 250 PSI as a starting point, possibly

300 PSI. Yes it will vary with load and conditions.

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

I was figuring out a system for a two story house I was interested

If it were me I would not use a single system that incorporates a cold room/freezer and air conditioning.

Compressors that are suited for freezers are not good for air conditioning and to a lesser extent visa visa. Using a large air conditioning compressor to cool a freezer would work, but be expensive to run, and there could be capacity problems. IE the compressor running down on vacuum because it is too large for the freezer. (Yes for the trolls, the LP switch would stop it.)

The other thing is that as soon as the air conditioning side cut in the suction pressure would rise far to high for the cooling in the freezer.

As on a design day one could (All things being equal) can expect the cooling would be running all day 100%, and therefore there would be no cooling for the freezer.

One other point is that the semi hermetics would need to have some sort of oil exchange or you could run out of oil in one of the compressors. Care would be needed on the pipework for oil return, because of lesser velocity when the compressors are unloaded

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

Unloading compressor for a 2 story house could be fine, I actually have a Carrier 06DA818 on my home with an unloader on it. It is around 6 ton capacity 4 cylinder unit. The house is single story. Again the system is on R22.

The condenser has 2 x 3 phase fans and they switch from star to delta to increase the fan speed controlled by pressure switches, it works well with 4 stages of control, as the condenser is a bit oversized and I control the head pressure under 250 PSI on days up to 40 c (104 f), which is the highest I have seen it here.

Originally I installed it because I had thought of adding an extension to the house, but that is not going to happen, however it works well as it is.

I am not altogether happy with the unloading as it does not shed anywhere near half the power when unloaded.

I did design and install a multiple fan coil system in a home using a Carrier 6D 6 cylinder unloading compressor years ago, it worked well. That one had 2 unloaders on it. IE 100%, 66% and 33%.

=====================

Reply to
<ramrod

True

But of course you jump in without knowing anything of the conditions here, for instance, the lowest temperature recorded here was 7.3 c (45.14 f) many years ago, in the last 10 years it has dropped to 9 c (48.2) twice early in the morning, other years we see it drop to 11, (51.8 f) two or 3 times a year again early in the morning. During the cooler weather it usually gets up to 27 c (80 f) during the day so the houses do not get icy cold and require little heating, mainly early in the morning.

Hence the size of the outdoor coil and the amount of air going over it can control the suction pressure considerably, this will have a big effect on the head pressure. IE a large outdoor coil and high fan speed will keep the suction pressure up considerably.

Looks like someone needs to teach you basic refrigeration.

Reply to
<ramrod

Ok.... if you had told us that you frankensteined together a system that was grossly oversized from the start, that would have made a huge difference. If this 6 ton commercial unit is only feeding 3 rooms, this begs questions... how big are the rooms?? Where are you dumping the excess air when the dampers are closed?? Where is the house located? How big is the house? Is this system cooling the entire house? or just the 3 rooms you mentioned? What are your average power bills while running this beast??

Reply to
Steve

Sure... as long as you can keep the SP above 59F @ 400cfm/ton evaporator airflow otherwise, your gonna have issues

Looks like if you laid *EVERYTHING* out in the first place instead of giving little dribs and drabs of information... My crystal ball is in the shop.

I figure either your a troll, or an EE

Reply to
Steve

SP (Suction Pressure) is measured in PSI in imperial measurement, not degrees. Suction Temperature is measured in degrees.

I have seen many evaporators with a suction pressure of around 52 PSI (around 28 f) on R22 and they do not ice up.

As I said I did not need 1st year apprentices guessing at answers.

Goodbye Steve.

Reply to
<ramrod

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.