Two Pipe System

Are you trying to provide air conditioning to the building or is this for the water supply?

Is for Chilled Water System for Air Conditioning

Regards

A two pipe chilled water system is probably the most commonly used air conditioning distribution system in use today. In the hotel/motel industry, the most common systems consist of wall mounted, individual air cooled room air conditioners. Large facilities that contain dining rooms, conference/meeting rooms, etc would have a central system, which in most cases would be achilled water system.

Hydronic systems are closed systems in that the water is circulated in a loop from a chiller, for example, through the air conditioning unit, air handler, and returned to the chiller. In a high rise system, the main concern is providing sufficient static system pressure to keep the system full of water. If your building has 18 stories, then we're looking at a building some 180 feet in height. If the piping extends to the top floor and you fill the system, the pressure at ground level would be 180' water column, or approximately 78 psi. This would be the minimum pressure required to maintain the system. Obviously, the higher elevation in the system, the lower the system static pressure. And this important.

Standard pipe, valves and fittings are rated at 150 psi, and that would include pumps and their accessories. In systems such as these, the pumps are sized to circulate the required amount of water, in gpm, at a dynamic pressure, feet of head, sufficient to overcome the resistance, pressure drop, created by moving the water through the piping, valves, fittings, and equipment, chiller, air separator, etc. This "dynamic head" is in addition to the static head of the system, when added, would be the total system head during pump operation.

So, as far as the hydronic system is concerned, all the pressures are within the component's ratings, there shouldn't be any reason to interject a heat exchanger in the sytem, but you must maintain system static pressure. To do, that the make-up water supply pressure must be sufficient to inject water into the system.

If the domestic water supply pressure, furnished by the utility, isn't high enough to provide sufficient pressure at the top floor, then a pressure boosting system must be used to augment the "city" pressure. By using as much of the city pressure as possible, the boosting system could be placed on an upper floor. This would be the point where the hydronic system make-up water should be introduced. An equipment room would be utilized for these systems. Here you could install the make-up system, air separator, and the chilled water circulating pump. You might consider a VFD for the pump, which would provide a real energy saving feature, particularly when the motel is only partially occupied.

Good luck

g scott

GOOD LORD, where did I get motel/hotel??? Scrub the references.....I think my description and analysis otherwise would be valid.

When I ponder, I sits and thinks, sometimes I just sits.........and this was one of them,

g scott

G Scott--

Glad to know I'm not the only one who sometimes just sits... Good idea about using a Variable Frequency Drive (VFD) for the motor, because most systems only need their full thermal capacity for a few hours each week, or even less at certain times of the year. Therefore, using a VFD set to adjust its speed according to the temperature differential of the system is going to be very energy-saving. I don't have the means to do any calculations, but I believe the return on investment will be less than 1 year.

I also suggest that experience with buildings with large floor areas shows that the general heating and cooling needs are such that the excess heat generated towards the core of the floor can be used to offset the heating needs near the exterior. I don't know what the climate is at the proposed site in Costa Rica, but a good heat load calculation, looking at zones within the building as well as overall shell gains/losses will give good guidance on this.

It would be good if the design could incorporate as many energy-neutral concepts as possible. There are many good recent examples of this out there---frequently on university campus locations, but also in the commercial business world. I believe that in most of these, the cost of the energy conserving features was easily recovered in operating cost savings, partially in construction cost savings, and also by increased user/tenant comfort and satisfaction.

JMM

Thanks a lot,

Great info. I have a contractor asking for the operating pressure of my HW, Primary Condenser Water, and Secondary Condenser Water systems. He needs this info to order his PRVs.

I have a cooling tower on the roof of a 21 story building, the plumber has provided a fill on the roof. My heat exchanger, primary and secondary pumps and secondary condenser make-up water fill is in the cellar. My city steam to HW heat exchanger, HW pumps and the make-up is also in the cellar.

So what is the operating pressure of these systems (for purposes of sizing the PRVs for the makeup water)? Do I add the static head (roughly 90 psi) to the dynamic head? Is that the pressure that the make-up water needs to exceed in order to inject make-up water into the system? What should my circ pumps be sized for? The static head, the dynamic head, both or some percentage in the middle?

I have a similar question on the domestic service. The owner wants to change some fixtures in the penthouse. These fixtures require a min. pressure to operate. If I know how much pressure I have at the POE and I know how much pumping capacity I have, how do I determine what is left at the penthouse? Is it the static plus the dynamic head minus my available pressure?