heat reclaim

[Sledge]

I have a customer with a small grocery store, and of course, limited funds.

The problem is heat.

He has numerous fridges with compressors mounted underneath.
The issue focusses around the walkin boxes and the heat coming from the condensors.
He has 3 walkin boxes, condensors mounted on top; one 1/2 hp fridge 134a, one 1/2 hp freezer on 404 and one 3/4 hp on 404.

My initial plan was to install a multiple pass air cooled condensor on the roof, and remove the old coils. This would require installing headmaster controls on each circuit, along with replacing the receivers, due to the low temperatures it would face.

The problem with this approach, is that the customer hasnt had to pay for heat in past winters, due, in part, to the heat coming off these condensors. This is an estimated $2000/month saving

The solution we are considering is installing the rooftop condensor and trying to use it in the summer, but switch to the inside existing condensors in winter.
Is it possible to install solenoids to divert the discharge to the new rooftop condensor in summer, but maintain the flow to the existing condensors in winter. Anyone seen anything like this before?

Any ideas?

[Peter_1]

Yep, we've done it, you need a condenor pressure regultator and a SV, preferable a NO one.
I will try to make a schematic this evening

[taz24]

Is it possible to install solenoids to divert the discharge to the new rooftop condensor in summer, but maintain the flow to the existing condensors in winter. Anyone seen anything like this before?

Any ideas?


The short answer is yes it is.

There are controls and 3 way valves that are in use now that divert discharge gases to indoor heat reclaim or outside condensers.
They are readerly available and work very well.

Have you considered using water to cool the condensers and then use the water to either heat the shop or to be cooled outside.

Cheers taz.

[Brian_UK]

One other option perhaps is to design a ventilation system to remove the heated air from the the top of the units.

A simple damper arrangement could divert the warm air back into the store during the winter.

[bill1983]

we have come across this problem several times and have utilized extract fans at high level ducted down to the condensers and controlled off a single thermostat to control shop temperature. the extract fans have been boxed in to meet the tops of the cabinets to remove the effect of the fans from removing shop air. simple cheap effective
bill

[Peter_1]

Taz, a 3-way valve is expensive and can't be find that easily. Valve can also be stuck so that the flow is blocked.
In your case, both condensors must be large enough to condens the discharge flow.

I will try to explain how you can do it very easily: discharge and a T junction to 2 condensors: outside (OC) and inside condensor (IC).
Condensors can be of different size.
IC condensor has a SV, the IC a condensor pressure regulator (CPR)

If you need heat reclaim, you energise the SV of the IC and the flow will take the way of the least resistance. The CPR is set to a normal condensings pressure in summer. All what can't flow through the OC will automatically bypassed proportionally to the IC.

If you don't need any longer heat reclaim, just de-energise the SV again.

Install also at the outlet of each consensor a NRV so that condensation can't occur in the stand-still condensor.

[gas_n_go]

Am I missing something here? What it sounds like to me that is being described is seperate systems sharing one big coil. Not a rack setup, just multiple passes being piped seperatly for each unit, is this correct?

Heat reclaim can be acomplished but if Im reading your post right you would need a valve for each system. That may or may not turn out to be cost effective. In either case I think I might look into adding a hotwater reclaim into the works. Summer and winter they need hot water so I would utilize my btu's there first and then whatever is left I would use for heat or dump out on the roof.

I would also point out to your customer for whatever he thinks he is saving in the winter with his current set up he is giving back plus some in the summer by removing that same heat being added to his store with his A/C.

I have a question reguarding all this to you guru types. When I was younger first getting started in the trade. I was involved on a job that had a heat reclaim issue and I inquired why hotwater heat reclaim typically was attached to the low temp rack. The answer I got was that even though it was a lesser capacity condensor, it had more usable btu's in relationship to water. This answer has never sat well with me and was wondering if someone can explain it better to me, or was the guy just blowing me off with some double talk? Isnt a btu a btu?

[The MG Pony]

Water seems to be the most logical, I am in the same possition, What we have concluded was to convert all systems into water cooled units, tap all units into one main out side condencer, To that condencer have an internal water source space heater that feeds off the discharge water.

This way we get a unit designed for air heating and we get a good cool water returned for the condencing plants. Water piping is cheaper then refrigerant piping so costs are saved, each system can easily be serviced with out effecting any other. Refrigerant charges are kept small & self contained. In the event of a catastrouphic accident every thing just gets wet!

Cons are you have a circ pump added on but thats not much of a draw back being you gain massive flexibility

More we look at it better it is.

As I understand it lowewr temp systems tend to have higher temp discharge.

[Dan]

I was involved on a job that had a heat reclaim issue and I inquired why hotwater heat reclaim typically was attached to the low temp rack. The answer I got was that even though it was a lesser capacity condensor, it had more usable btu's in relationship to water. This answer has never sat well with me and was wondering if someone can explain it better to me, or was the guy just blowing me off with some double talk? Isnt a btu a btu?

I don't think there has been any hard and fast rule regarding why low temperature racks were favored for hot water in US supermarkets. I would offer two possible reasons that would point people in this direction, however.

1. Early hot water reclaim systems had limited refrigerant flow capacities. Originally, single compressors were dedicated for hot water for this reason. Low temperature compressors have less flow than their medium temperature counterparts, thus, even as tanks were constructed to accept large flow amounts, the low temperature racks would encounter the least pressure drop.

2. Much of what a hot water tank does is merely desuperheat the refrigerant. Low temperature applications will generally have a higher sensible temperature, thus be able to attain temperature more quickly. Perhaps the higher discharge temperature is what the fellow was referring to?

[US Iceman]

Perhaps it is due to the longer expected run times you see on low temperature systems. you would have a greater opportunity to collect heat over a longer period.

[gas_n_go]

ty you both for your responses