This article was originally published in the November/December 1999 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online November/December 1999

Fuel Use in Multifamily Buildings

by F.L. Andrew Padian

F.L. Andrew Padian is a housing specialist with Steven Winter Associates, a building systems consulting firm based in Norwalk, Connecticut.

A survey of New York City's low income multifamily buildings reveals distressingly high fuel uses for heating and domestic hot water. About 5% of these buildings had been recently rehabilitated--but not with energy conservation in mind.

The top-floor tenants are using the double hung zone valves--better known as windows--to solve their overheating problems.

Multifamily Statistics

Average number of apartments in a multifamily building nationally: 14

Percentage of total housing units in the Northeast that are multifamily: 21%

Percentage of multifamily households nationally that have electric domestic hot water systems: 38%

Percentage of all U.S. buildings with more than 50 units that are located in the Northeast: 42%

Percentage of multifamily households nationally that heat with electricity: 43%

Percentage of U.S. multifamily buildings located in cities: 53%

Percentage of U.S. multifamily buildings with 5 to 19 units: 58%

Percentage of multifamily households nationally with incomes under $25,000: 61%

Percentage of multifamily dwellers nationally who rent: 90%

Average heated floor area of existing multifamily apartments in the United States: 804 ft2

Average heated floor area of existing mobile homes in the United States: 921 ft2

The Math

Calculating fuel use normalized by weather and heated area can be a sophisticated affair requiring the use of a fuel analysis program such as ES-QUIP or PRISM, but a good approximation can be made with a pen, some paper, and a calculator. The method below can be used to get such an approximation, but it requires that there be one source of fuel for both heat and hot water, and that fuel for both uses be metered or billed to the same account. This source could consist of a single oil tank or a single gas meter that feeds a central heating and hot water system, separate or combined.

Building owners, managers, and cooperators of multifamily buildings can produce complete fuel records for one (and preferably two or more) years. For these records to be precise, in cases where the building uses oil, deliveries should fill the tank each time, so there is an accurate record of fuel use between time periods. Many managers feel that if they order oil at the same time, in the same amount, each time the tank gets to a certain level, they will be accomplishing the same end. Unfortunately, this very unscientific method is fraught with human error and can make the calculation very inaccurate.

Break down all fuel use by delivery date, number of gallons of oil or therms of gas, and cost--people who are spreadsheet savvy could create a program to do this. Then calculate the average daily fuel use during nonheating months and multiply it by 365. This product is the hot water or base use. Take the total annual fuel use, separated out each year from date to date (from June 1, 1998 to June 1, 1999, for example) and subtract the base use. The amount that remains is the annual heating use.

Get the total heating degree-days for the winter in question from a local weather-monitoring station. Calculate the total heated floor area of the building. Multiply the heating fuel consumption by the number of Btu in each unit of fuel. Divide the product first by the heated floor area of the building and then by the number of HDD for the winter in question. The result will be the fuel use normalized by weather and heated area in Btu/ft2/HDD.

After the installation of a new steam boiler, the fuel use for this building was less than that of the average multifamily building, although it is more than 50 years old and it has multiple exposures to cold and wind. 
Multifamily buildings with more than five units make up about 17% of all U.S. housing, yet scant information exists on the fuel use of these building in specific locations (see Multifamily Statistics). Without understanding the current fuel use in buildings, it is impossible to gauge the potential for savings in the future. To answer this question for the New York area, the Association for Energy Affordability (AEA) conducted a study of fuel use in 401 existing low income buildings in New York City in 1994. Measurements were taken of fuel use/ft2, with baseload removed, and adjusted for weather fluctuations. Building Background The 401 buildings that were analyzed were all candidates for New York State's Weatherization Assistance Program (WAP). Before the buildings were retrofitted with any weatherization measures, AEA performed extensive energy audits on each building. During these audits, information was collected on apartment size, wall and roof construction, heating and distribution system design and efficiency, appliances, occupancy levels, and other details. Building simulations and fuel monitoring were conducted using two DOE-supported software packages, the Energy Audit using the Queens Information Package (EA-QUIP) and Energy Savings using the Queens Information Package (ES-QUIP). Both of these programs were developed by Queens College. AEA collected data for at least one and typically two years of fuel use for every building.

All of the buildings had a central-heating-and-hot-water plant that ran on either oil or gas, which was paid for by the owner. In more than 90% of the buildings, the tenants paid for their own electricity. In New York multifamily dwellings, electric costs are typically higher than heating-plus-hot-water costs, even if the occupant pays for both, because of the high cost of electricity. In this article, however, I address only heating and hot water uses.

All of these buildings can be described as both low income and distressed. Most of them needed to have their boilers significantly upgraded or replaced. Many of them had their original wood windows (which were up to 75 years old), no roof insulation, and antiquated controls for both the boiler and the domestic hot water system. Typically, the heating plant was one-pipe steam, and the same system also provided the hot water.

The Numbers In New York City, the 401 buildings that were studied averaged out at 24 Btu/ft2/HDD (heating degree-days) for heating fuel, or somewhere between 1 therm of gas and 1 gallon of #2 oil/ft2 per year for heat. According to the Energy Information Administration, the average fuel use for heating multifamily buildings in the United States is 12 Btu/ft2/HDD, or half what was used to heat the low-income buildings that we studied. Even more disturbing is that the average building used about 47% of its primary fuel to make hot water. For one building, these numbers skyrocketed as high as 75 Btu/ft2/HDD for heat, and in another building 91% of the fuel was used just to make hot water.

Although most of our sample consisted of old, unrenovated buildings, about 5% were recently rehabilitated affordable low income housing. Since these buildings had recently been rebuilt, it would be reasonable to expect that simple energy technologies would have been employed to make them more energy efficient. Unfortunately, in many instances, rehabilitation choices were based on first costs, resulting in ballooning operating expenses. Indeed, these buildings came to our attention when the not-for-profit management company or low income cooperators called WAP for assistance because they could not afford to pay their fuel bills.

During the audits, it became apparent that most of these recently rehabilitated buildings with high fuel use suffered from the same fatal flaws. In all cases, low-efficiency atmospheric gas boilers had been installed for both heating and hot water production. The systems were generally oversized for the buildings, and the heating systems had no night setback controls. The radiators in the apartments were not sized correctly for the rooms, causing overheating when the outside temperatures were in the 30°-40° range, a problem that the tenants solved by using the infamous double hung zone valves--also known as windows. All of these buildings had only one heating zone. In most of the buildings, the insulation was poorly installed. In extremely cold weather, the insulation failed to perform properly, and the buildings went from overheated to underheated, with the boilers running constantly. Finally, even though gas costs 80¢/therm in our area and oil costs 80¢/gallon, none of the rehabbers chose to install oil or dual fuel boilers in order to get a cheaper first cost fuel.

The Message What do these numbers tell us? First, they tell us that fuel use analysis should be mandatory at the beginning of any building investigation (see The Math). Such a fuel-use analysis points an auditor in the right direction when he or she first walks through the building at the start of an audit. For the building that used 91% of its fuel to make hot water, a modest program of adding good showerheads and aerators reduced overall fuel use by more than 30%.

Second, high fuel use for heating is typically caused by overheating, and by lack of night set-back controls. Regrettably, the building with the highest fuel use for heating (75.3 Btu/ft2/HDD) was a two-year-old gut rehab that featured all of the fatal flaws described above. Some of these flaws cannot be easily resolved without spending a lot of money on re-rehabilitating the building. Although it would not be accurate to say that all new affordable rehabs in New York City are inefficient, those that were referred to WAP had heating and hot-water fuel use almost double the average.

Third, excessive fuel use does not depend upon the age of the building, or on its orientation, number of floors, or number of apartments. Nor does it depend on the type of fuel used. There were high and low consumers in all categories. Management and maintenance were the most important factors in determining each building's fuel use. The more management watched fuel use and the better it trained its staff, the more efficient the buildings were. Management that practiced regular maintenance on all systems rather than only conducting emergency repairs also tended to use fuel more efficiently. And smaller owners, who were involved directly in building management, generally used fuel more efficiently than absentee owners, who left the building's management to large companies.

A quick analysis of these numbers for a large range of buildings and apartments--totaling more than 14,000 units of housing--helps to provide a yardstick for determining the fuel use in low-income distressed housing in New York City. This study may also aid in the analysis of other multifamily buildings by serving as a general comparison guide.


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