hvac_system HVAC = HEATING, VENTILATION & AIR CONDITIONING SYSTEM by David Lawyer, Revision 5 1995 INTRODUCTION FRESH AIR PROBLEM AIR CIRCULATION SYSTEM: EVAPORATIVE COOLER SMALL HEATERS WARM WEATHER VENTING POLICY ROOF & WALL VENTILATION VENTS PERCENTAGE FRESH AIR FILTERS INTRODUCTION Throop Church is heated & ventilated by 3 blower-furnaces in the furnace basement. This is a "forced air" system using natural gas for heating in 3 furnaces. The 3@ blower-furnace pairs are for: 1. Sanctuary (large blower to W) 2. Throop Hall (blower nearest doors) 3. Upstairs (blower near SW corner). To ventilate only, the blowers are turned on but the gas is kept turned off. See the file hvac_hardware for details of the furnaces, blowers (fans), motor controls, and air washer (doesn't work) in the basement. The furnaces & blowers are controlled by toggle switches at the top of the basement stairs. There is a switch for each of the 3 furnace-blower pairs. Each switch has 3 positions: heat, off, vent. In the vent position only the blower is on and no heat is supplied. There are also timers on the N. wall (Minn. Honeywell Da-Nite Timeswitch) for each of the 3 furnaces/blowers but they are "set" up for "always-on" by allowing the timer wheels to not turn by loosening a screw. Thermostats in the sanctuary, social hall, and N room upstairs regulate the temperature. Each furnace has an input, output and pilot thermostat. See hvac_hardware for more details The grilles in the walls (or floor) which connect to ducts are registers for the heating-ventilation system. However, in some cases the duct ends after only a foot or so, and thus the grille is serving as a vent and not really as a register. Thus a grille may be either a vent or a register. FRESH AIR PROBLEM Ventilation is a non-obvious problem. All the floor grilles in the sanctuary and all of the low wall grilles in Throop Hall (W wall) lead directly to the dirt crawl space under the building. This is because the crawl space is used as a return air duct to recycle air. At present there is no easy way to avoid getting air from under the floors into the building. In the winter, much of the air from both the sanctuary and Throop Hall flows via the crawl space to the intake of the ventilation system. This also happens in the summer, but then fresh air is mixed with the air from under the building. The major mixing point is in the intake plenum which one may stand up in. There should be a damper to permit 100% fresh air ventilation but there isn't (but see below. To make the air fresher, there is an air washer in the basement which once cleaned and cooled the air for the entire church. But at some point two additional blowers were added which bypass the air washer. So if the air washer were operable today it could now only improve the air for the sanctuary. The ventilation ducts under the building need cleaning. But most of all, we need to figure out how to best utilize our ventilation system and how it should be modified so as to economically provide fresher air for Throop Church. PERCENTAGE FRESH AIR: The following is from the former version of "Using Throop" but is too complicated to put there. It needs to be better incorporated into this document. The percentage of fresh air depends in part on the setting of the large intake air door in the basement and the return duct damper. The "intake door" is hidden (you can't see it) in the SW corner of the basement and is on a (visible) rope and counterweight. The setting of the intake door and return damper may be noted on a card next to the toggle switches. The percentage of fresh air depends on many factors including which ventilation blowers are turned on. Rough estimates are: H = Hall (Throop Hall), R = Rest of building (sanctuary & upstairs) % is percentage of fresh (outside) air Return Damper Position Open Closed Intake| Closed H:10% R:15% Don't use (no air for blowers) Door | Open See Below H:10% R:98% When both the intake door and the return damper are open, the results depend on which blowers are on: All on H only on H off others on H & one other on H:10% R:80% H:40% R:60% H:15% R:90% The reason why Throop Hall doesn't get much fresh air is that the intake air for its blower comes from a duct which is used (depending on the direction of air flow in this duct) both as a fresh air intake duct and a return duct. Drawing air from this duct may get a mixture of fresh and recycled air. This is why "vent" should be used for Throop Hall only as a last resort. The dirt crawl space (under the floor) is used as a return duct. The floor grilles in the sanctuary and the low wall grilles in Throop hall exit there. If the ventilation system has been off for a long time the air under the floor may not smell fresh. This is especially true for the sanctuary which needs to be aired out for perhaps an hour before using it. As air flows thru the crawl space, the air there becomes fresher. There is a little natural air flow in the crawl space from the outside since most openings have been blocked. Opening them would result in wasting heat by mixing more cold air from the outside with recycled warm air. Another complication is that most of the vent air to the upstairs exhausts to the outside (there is no return duct but there are vents to the attic which is vented to the outside). This loss of air from the building forces fresh air to enter the building (perhaps by the crawl space openings) regardless of the setting of the intake door in the basement. AIR CIRCULATION SYSTEM: Each blower is adjacent to its furnace except for the Sanctuary blower which is painted olive green and is in the NW corner of the basement. Output air from this blower flows thru a large concrete tunnel below the basement floor in order to reach its furnace. Access to this tunnel is via a trapdoor in the floor near the Sanctuary Furnace. This blower originally supplied air to the entire building. The system was designed with only one return duct which gets its intake air from the crawl space. The return vents (grilles) on the ground floors all feed directly to the crawl space. Upstairs, there are exhaust vents (grilles) which exhaust to the attic and outside. AIR NOT FRESH & RADON: The use of the crawl space as a return duct is one reason why the air in Throop Church does not always smell fresh. Tests have shown that the radon gas level in the ground here is low and that the level in the Sanctuary with almost no ventilation is about the same as the level in a typical US home (3 times the level of the outside air). Thus the use of the dirt crawl space as a return "duct" doesn't seem to generate an unacceptable level of cancer-causing radon gas, especially if a substantial percentage of fresh air is mixed with the return air (or if doors and windows are used for ventilation). The irony is that when the crawl space is not used as a return duct, the ventilation of this crawl space becomes poor and more radon gas accumulates there so that when it does escape into the building it is worse. Thus avoiding using the crawl space as a return duct might not help any in decreasing radon gas unless the crawl space were better vented to the outside. RETURN or SUPPLY GRILLES: With the exception of the restrooms and the Fireside Room the rule for determining the type of grille is that the low ones are for return (or exhaust air) and the high ones are for supply. In the Fireside Room the floor registers (grilles) are supply. In the restrooms, the vents (grilles) on the walls are natural draft and exhaust to the roof. In the Sanctuary, the grilles on the floor are return as are the ones low on the walls in Throop Hall. All of these return grilles empty directly into the crawl space. The registers high and low on the sanctuary walls and high on the walls in Throop Hall supply heat/air. CRAWL SPACE VENTS: If all blowers are on, the exhaust of say about 1/4 of the intake air to the outside forces about 1/4 of such intake air to be fresh. If the intake vent gate is closed, then such fresh air will be mostly supplied by the vents to the crawl space from the outside. There are 7 such vents: One on the W side (mostly closed by wood gates on the inside), two on each side of the sanctuary near the middle (mostly closed by concrete covers), one to the W of the tower steps, one on the E wall of the kitchen, one in the heat-vent basement, and one in the E room of the stage basement. These basements are vented to the outside via louvered vents so that crawl space air often flows thru the basements. EXHAUST TO OUTSIDE: The upstairs N. Room has 4 grilles (vents), 2@ exhausting to each attic closet. The S. Room (Morrison Room) has 2 exhausting to the E. attic closet and 1 exhausting to the W. attic closet. Air from the "attic closets" flows directly into the attic from whence it may exit to the outside. The main attic is well ventilated. Attic vents are found under the eaves (look with a flashlight while on the balcony above the kitchen) including the eave near the peak of the roof by the flat roof near the tower. A few small louvered vents are near the peaks of the gables. Air may also escape via the upper tower room thru the nailed-open trapdoor to the bell room of the tower and thence out the bell room louvered windows to the outside. Of course air may also exhaust thru open windows and doors. Most restrooms have vents leading to roof above them. Air will exhaust from these vents via natural draft provided that it is warmer inside (including the vent temperature inside the walls and thru the attic) than outside. This is true (the vent works) during the winter when the building is heated. During other times of the year the vent flows during the afternoon and evening when the building is warm. MISC DAMPERS: The sanctuary floor grills have dampers below them which can be used to disable them. In the Fireside Room floor supply registers don't supply much air. A damper for them exists next to the furnace. Other dampers exist in the basement. WOMENS ROOM: The register in the Womens Restroom is on the upstairs system which means that to heat the Womens Restroom by gas heat requires heating the whole upstairs. One may avoid this by using the electric heat in the Womens Room. INTAKE PLENUM: Most of the intake air for ventilation comes from the plenum in the SW corner of the heat-vent basement. This plenum is supplied air directly from outside via the Del Mar St. louver vents and from the return air vent which enters this plenum high up. One may walk inside this plenum and view the old air washer which also serves as an intake duct for the sanctuary blower. The amount of fresh air taken in from Del Mar is regulated by a huge wood gate (or door) which is moved by a counterweighted rope at the SW corner. To enter the plenum raise the south-most of the 3 access "doors" to the air washer. The fresh air gate is opened, closed, or opened part-way by manually raising or lowering the counterweight. RETURN DUCT: The return air duct is a large olive green duct high up on the W wall. The intake air for the Throop Hall blower comes from a tee in this duct. The return air duct has its intake in the crawl space under the cement floored tower narthex. Note that only part of the air found in the crawl space is actually recycled. Some fresh air enters the crawl space from the vents to the outside. AIR MIX & SANCTUARY EXAMPLE: When the fresh air gate is fully open, over half of the intake air will come from outside but some will still come from the return duct. For example, if the doors to the sanctuary are all closed and only the sanctuary blower is on, then air entering the sanctuary registers must exit somewhere and most of it will exit into the poorly vented crawl space. Much of this will enter into the return duct intake near the tower foundation. This will supply the intake plenum with air and outside air will be drawn in only to the extent that air leaks out of the sanctuary and the crawl space to the outside. Thus be sure to keep a sanctuary door open to exhaust air if you want fresher air. Note that the crawl space vents on the W. side have gates which were operated by ropes from the far W passageway near the choir room. To get to the (inoperative in 1994) ropes, open up the access doors in the "bookshelf" shelves. ALL FRESH AIR: One way to get all outside air would be to shut off the return duct in the basement in the NW corner but there is no damper at this location. However there is a damper near the SW corner to shut off the return duct in such a way that all the intake air to Throop hall will be recycled with all fresh air supplied to the sanctuary and upstairs. To get nearly 100% fresh air, one could shut off this damper, open the outside air vent gate, keep the Throop Hall blower off, and ventilate Throop Hall by opening its large doors to the patio (and possible use a large fan). RECYCLING AIR: In the winter, the basement outside vent gate to Del Mar should be nearly closed to recirculate hot air (mixed with a smaller amount of fresh air). Of course this will recirculate any smoke in the air if people are smoking and a small amount radon gas. All 3 furnaces draw their intake air from the same return duct so that smoke in Throop Hall will spread throughout the Sanctuary and Upstairs if all the blowers are on. However some smoke will escape to the outside via the upstairs vents leading to the attic. NON-WINTER POLICY: In the non-winter months, the gate should be open so as to provide fresh air for ventilation. However, it will save energy to simply open windows for ventilation and avoid using the blower. While the windows in the sanctuary do not open, one may open the doors to the outside which should provide enough ventilation for a small congregation provided there is some breeze outside and not too much street noise. To reduce street noise, open only the door to the parking lot and the S door to the stairwell and Throop hall. This requires that either upstairs windows are open or that at least one patio door be open to the outside. EVAPORATIVE COOLER (alias Air Washer, Humidifier) (not working) This both cools and washes the air for the sanctuary, except to the extent that air is recycled. Since in the summer (when the cooler might find good use) the outside air temperature is often lower than the inside air temperature (especially in the evening), recycling of air is often not desirable. Thus in the summer its main use would be only cooling the sanctuary. Originally, this cooler (and its fan) supplied the entire building with clean air but the modifications made when the existing furnaces and Utility blowers were installed bypassed it for all areas except the sanctuary. Thus if it were restored it would primarily be of use only for cooling the sanctuary. Cooling is needed more on the 2nd floor as this picks up heat from the roof. I am told by Carrier that cooling is the main use of an "air washer" and that cleaning the air is a secondary purpose. In order to keep the air clean, the water needs to be also kept clean (i.e. replaced with new water every month or so). Since the return "duct" is the crawl space, such air could have some dust in it, especially since the floor of the crawl space is dirt. However, only part of this return air will go thru the air washer. This evaporative cooler will help bring down the temperature of the air to a little above the wet bulb temperature of the air, which on a hot day might be say 75 deg. F. However it is of little benefit under conditions of high humidity. I have been told that evaporative cooling would have been ineffective during the hot spell of Sept. 23-25, 1991 due to high humidity. In addition, it is probably best to use it only when really necessary since one is not apt to be too comfortable under conditions of high humidity produced by the evaporative system. As for washing the air, the dry fiberglass filters used on the intake to the blowers clean the air to a certain degree (perhaps 35% of the dust is removed (but the water washer can probably do it better). WARM WEATHER VENTING POLICY The problem here is mainly that of keeping the church cool. If the huge humidifier worked, there would be lees need for a clever warm weather ventilation policy. Without any air conditioning, it may be possible to keep the Church reasonably cool just by intelligently ventilating it. To do this one probably needs a computer control system. This might be economically feasible using a used computer since one does not need much computing power. One could also use part of a personal computer used for word processing provided that it had a multiple process operating system such as Unix. The sensors (include analog/digital conversion) may not be cheap, however. The same system would be used for control of heating in the cooler months. Utility bill often average over $1000 (including electricity for Henry House) a month (1991) and while a computer control system might not save much in the summer, it would provide more comfort inside the building. For a summer 24 hour period, one might use a policy similar to the following: In the evening, keep the vent blowers on using outside air to cool the building which has become warm from the daytime sun. However, only do this when the temperature of the inside air is at least slightly warmer than the outside air. Late at night the building exterior temperature may drop below the air temperature due to radiation loss to the night sky (depending on cloud cover). Thus the ventilation may need to shut down to allow radiation cooling to cool the building down below the outside air temperature. Then in the morning the building is cool. It may even be too cool, in which case one might turn on the heat for a short period of time just before people are to use the building, heating only that portion of the building which is to actually be used. If the building is too cool, but the outside air is warm, then one may save heating costs by admitting outside air instead of turning on the heat. One might ask: Why cool down the building at night to a temperature so low that the building then requires heating in the morning? The answer is twofold: 1. The unoccupied parts of the building will not require heating in the morning and they may be use a heat sink for cooling the building later in the day. 2. The building itself (some of it is made of brick and concrete blocks) has a much higher heat capacity than the air in the building. This solid structure will retain much of its coolness later on in the day even though heat has been applied for a short time to the building air. As the building structure heats up (or on a hot day when no morning heating was needed at all) decrease the intake of outside air to just the level necessary to maintain air freshness. When it starts getting too warm in the occupied sections of the building, recycle the cool air from the unoccupied cool sections of the building (e.g. the Sanctuary) to the occupied sections. The above is easier said than done. To both save energy while decreasing the flow of intake air would imply slowing down the blowers which can't be done at present. A less efficient method would be to cycle them on and off (for example 20 minutes on and 40 minutes off). The intake air door for the intake vents on Del Mar needs to have a remotely controlled motor drive instead of its current manual operation. If it eventually becomes too warm, there are then 2 ways to go: Use room air conditioning as exists in some of the upstairs offices or use evaporative cooling by means of human sweat. To facilitate the last method, open all windows and doors wide and blow large quantities of air thru them with large fans. This has been done in Throop Hall. It becomes obvious that optimal control policies will be complicated. Only a computer could do an good job of controlling the situation provided it was furnished with well conceived algorithms and parameters. There are complicated trade-offs such as trading fresher air for hotter temperature (by admitting more hot outside air). Much more fresh air venting is needed when people are smoking and this may make them uncomfortably hot. Should non-smokers have to suffer both the smoke and the hot temperature? While few Throop members smoke, Alcoholic Anonymous groups and drug addicts anonymous (called an euphemistic name) often smoke a lot. The amount of fresh air venting to do at night depends on the probability distribution of the weather for the next day. The problem is one of stochastic optimal control. As the night progresses, the probabilistic forecast for the next day changes. I can't find any digital source for such data. One also needs a thermal model of the church building. Perhaps someone has already worked on this problem and one might first want to do a literature search. SMALL HEATERS There are two small heater vents on the roofs. One is for a wall heater in the basement dressing room (under the stage). The other leads to a 2 vent holes in the walls of the SW corner of the church: one in the S wall of the Choir Loft and another below it in the Choir Dressing Room. At one time gas heat may have been used there. An electric heater was on the W wall of the Womens room. It was removed in 1992 due to a defective switch and alleged higher than normal voltage (but I checked the voltage and found it to be normal). In the attic above the upstairs' offices there are terra cotta chimneys which don't go thru the roof. This implies that at one time these rooms had their own gas heaters in them. Could they be reinstalled to conserve energy by local heating? ROOF & WALL VENTILATION VENTS Of the 4 restrooms in the Church, all but Throop Hall Womens has a vent on the roof. The Men's has a rectangular vent which exits on the outside gable wall of the Sanctuary balcony thru horizontal louvers. The others two have large circular vents on the roof. The projection booth in Throop Hall also has a vent. As of 1992, none of these vents were supplied with blowers and air flow in them is at times nearly nil. In 1923 such vents probably did not require blowers. The kitchen has 4 forced air vents. One over the dishwasher exits on the N. exterior wall. The two near the refrigerator exit thru one vent in the E. exterior wall (each has its own switch). The range vent hood exits on the wall facing Del Mar. It has air pressure activated louvers. On the roof over the Ministers Study is a large mystery vent. Where does it lead? Trace it thru attic. Could it be a disconnected kitchen vent no longer used?? FILTERS The filters are the same size as the ducts, but should have been of much larger cross section than the ducts. Thus the filters tend to slow down the air, especially if they are filled with dirt. The filters system are obviously a patchwork modification and need to be redesigned.