Solar Power Plants, Orifice Vent Holes, District Heating

Readers Ask: When and Where Is the First Solar-Hydrogen Power Plant Being Built? What Is the Use of Vent Hole in the Orifice Plate? How to Upgrade Buildings' Heating Systems from "Leningrad Design" to a Current Design?

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c. The design calls for hole (vent or drain) to be tangential to pipe bore. This is hard to accomplish with the usual tolerances.
d. Hole size is small, so the orifice coefficient is that of a thick plate orifice, not a thin plate. Correction for additional hole area is poorly proven (and size can change with time).

Some recent experimental work is being undertaken at UK NEL. See “Improvements in the Measurement of Gas Flows with Entrained Liquids Using Orifice Meters.”

Ian H. Gibson

A: I would mention that the vent hole is used in horizontal lines only, and it shall be tangent to the upper part of the pipe. I think that in addition to vent application, it is worthwhile to mention the drain function in wet gas service, to avoid build up of liquid upstream of the orifice plate still in horizontal lines. In this case the drain hole shall be tangent to the lower part of the pipe.

Alberto Rohr

Q: Our Soviet-era buildings have been thrown together without any consideration for energy conservation. In their “Leningrad design,” the apartments have no thermostats, and in some buildings, even the radiators are piped in series, so the first apartment is overheated and the last gets practically no heat at all.

The heat source is hot water generated by burning natural gas and pumped from a district heating plant. We are in the process of improving the controls of these buildings. Can you provide advice on how we should do this?

Zbigniew Kaminski

A: In my book Post-Oil Energy Technology, I described how the energy consumption of buildings can be minimized (often cut in half). These strategies include making the buildings self-heating, eliminating chimney effects and optimizing district heating plant controls.

In optimizing district power plant, the first step is to take advantage of waste or free energy sources (incinerator, cogeneration, industrial waste heat, geothermal, solar) to minimize the use of “pay heat” as you generate the 200 °F hot water supply for the district.

To minimize the cost of pumping, variable-speed pumping stations should be used, and their pumping rate should be modulated to keep the differential pressure between the supply and return headers constant.

In the individual buildings, you should provide a heat exchanger in which the 200 °F hot water received from the district keeps the “secondary” hot water (SHW) in the building at about 180 °F. The SHW system should be provided with its own storage tank and with a variable-speed pumping station to keep the pressure difference between the SHW supply and return headers in the building constant.

In the individual apartments, you should use “hydronic fan convectors” and should provide on-off controls for both the radiator fan and the solenoid on the SHW supply (wired or unwired). Naturally, you should install a temperature sensor in each room, which can also be wireless (

If you want to use state-of-the-art controls, each apartment could be provided with a central comfort control (CCC) unit that contains all the comfort-related information and setpoints, which are also accessible by both telephone and through the Internet. This intelligent thermostat measures the temperature in each room and keeps it on its individual setpoints by leaving the SHW solenoid and fan in their last positions if the room temperature is within 1°F of the setpoint. If the temperature drops to the lower limit, the fan starts and the SHW solenoid opens. One the other hand, if the temperature reaches the upper limit, both close.

The room temperature set points can be programmed (locally or remotely) according to occupant’s preference, time of day, day of week, occupation, etc. In addition, the CCC could also keep records of the actual conditions in each room, the rate of instantaneous heat flow into the apartment (SHW flow times the temperature difference between supply and return) and the total heat consumed per day, week, month, etc.

Béla Lipták

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