Modular Boiler & Domestic Hot Water Heater Upgrade: System Analysis and Design

Facility Description

Country Club Gardens is a residential building complex composed of fifteen two-story buildings. The complex accommodates 236 families or approximately 590 residents. Combined gross area of the buildings is approximately 198,800 s.f. The facility is approximately 25 years of age and all of the heating and domestic hot water systems are original to the building. Each building is currently served by one 700 MBH heating boiler, one 400 MBH domestic water heater, and two DHW storage tanks, all located in the basement.

Project Origin and Goals

The heating and domestic water equipment was at the end of their expected service life. However, fuel efficiency, redundancy, and existing distribution problems were the driving force of this project. Most of the buildings were not able to meet heating demand during a design winter day at the extreme ends and fuel costs were 30% higher to other similar residential buildings. It was reported that boilers shut off during high demand periods. And in addition to the aforementioned issues, each building has substandard breeching height and renovating each breeching and chimney would be cost prohibitive.

MEP was subcontracted by an engineering firm to analyze, conceptualize a solution and design all of the heating and domestic water needs for the entire complex.

In order to meet the clients projected construction schedule, MEP was allocated two weeks to complete 100% design development documents.

Site Findings and Solutions

Boiler — Heating load calculations carried out by MEP indicated that the original equipment capacity was adequate. A modular boiler arrangement of three 300 MBH boilers were proposed, each capable of carrying 40% of the building’s heating and domestic water heating requirements. This modular layout would facilitate 80% capacity while one boiler is off-line for maintenance or repair. Furthermore, this arrangement would not require the relocation of the existing breeching in fourteen out of the fifteen buildings.

The source of the problem causing boilers to shut off was identified to be combustion and dilution opening related. Our field investigation revealed that the building was originally designed as a combination indoor/outdoor system or one which draws combustion and dilution air from within the basement and has minimal openings to the exterior. However, this original design was compromised when the boiler area was compartmentalized from the remainder of the basement, leaving virtually no means for combustion or dilution air. MEP designed an “outdoor air” ducted system or one which draws all air from the outside.

Hydronics — In order to address existing hating problems MEP surveyed the heating water supply and return piping to calculate hydraulic pressure losses. Each apartment’s finned tube radiation system was field verified in order to validate suitable capacity. Our calculations indicated that the existing pumps were undersized in both volume flow and pressure.

The existing heating piping system consisted of one constant speed pump and a 2-way (open/closed) valve for each apartment. This system is simple and satisfactory for buildings of this size and existing pump characteristics. On the contrary, this system is not recommended with the proposed larger pumps due to water hammer and noise. MEP designed two pumps arranged in parallel to provide means for backup equipment, each sized to handle 50% of the total flow requirements. The proposed system runs one pump continuously and turns the second pump on when needed to maintain proper flow during peak demand. This design kept a simple maintenance concept, provided proper performance and offered means to save energy during low demand periods.

Fuel Gas — The fuel gas piping distribution and sizes within each building is different although most of the buildings are of similar size and shape. Furthermore, some buildings are equipped with commercial fuel gas dryers. MEP surveyed all buildings and conducted pressure loss calculations to maximize boiler capacities.

Domestic Hot Water — The existing basis of design was modified from a direct water heater and storage tank arrangement to an indirect heater and storage tank arrangement. This piping and equipment arrangement allowed to reused the existing storage tanks (recently replaced), provided hot water generation backup, and has means to isolate storage tanks during low demand seasons to reduce energy losses.

Summary

MEP completed the design and specifications within schedule and the client approved the proposed design in the first submission.