XII Международная студенческая научная конференция Студенческий научный форум - 2020

Introduction

Considering the universal trends in sustainable development the essential task of the engineer among many others is to make engineering systems functional, safe and economically effective.

In building heating cost reductions can be achieved in several ways, including improving the boiler control strategy, giving the resident or building manager the ability to more precisely modulate the temperature according to the need, and altering the distribution of heat in the building in ways that better reflect demand.

A number of older studies exist, documenting the benefits of outdoor reset control in low-rise buildings compared to the aquastat-controlled constant water temperatures (sometimes with controls that turn off the boiler when outdoor temperatures exceed a certain threshold) that typified the previous generation of multifamily heating systems.

Outdoor reset controls alone can improve the overall performance of the heating system, but they are very sensitive to commissioning.

If the compensation curve is not adjusted properly, the overall heating energy consumption can be higher than that of a boiler controlled at a constant water temperature. Adding thermostatic radiator valves (TRVs) to radiators has been shown to reduce the system’s dependence on commissioning, but under- or overheating at low loads can occur as TRVs age. Additionally, correct use of TRVs depends on proper use by the tenants. It has been shown that the overall performance of a heating system is highly dependent on the algorithm for determining the boiler temperature set point.

Inferential models that, in the absence of real-time data, predict the average indoor temperature based on a simplified physical model, have been shown to be effective at increasing heating system efficiency.

Now another shift in control strategies is underway, one based on measured real-time average indoor temperatures in combination with outdoor temperatures.

New wireless technologies are available to cost-effectively monitor indoor space temperatures, centralize and automate thermostat set points, and, with the requisite level of control points in place, dynamically adjust heat distribution patterns. Control system manufacturers have produced case studies claiming benefits from outdoor reset boiler controls with indoor space temperature-based cutoffs of 25%–40% of heating fuel use. However, existing conditions and control algorithms are typically not well documented in these case studies. No known thirdparty, independent studies exist quantifying the effects of these improvements.

According to the available data in the USA there is a large stock of multifamily buildings in the Northeast and Midwest with space heating provided by centralized hot water or steam. According to the 2005 American Housing Survey, there are about 3.2 million occupied hydronically heated, low-rise multifamily housing units in the United States. Nearly 90% of these homes are in the Northeast or Midwest; with a large portion being rental units (40%) or occupied by the elderly (24%).

Most hydronically heated homes are older, with only 1% being classified as new construction (built within the past four years) in the 2005 American Housing Survey data. Many of these housing units are candidates for improved boiler controls as described in this project. Typically, residents of these buildings do not pay for heat directly (heat is not submetered). Losses from these systems are often higher than would be expected for buildings with centralized heat provided by a boiler serving multiple units (a significant number of apartments are overheated much of the time).

Upgrades to these heating systems often include the installation of new, higher performance boilers, yet heating costs sometimes remain high because spaces are too warm and the thermal distribution systems are inefficient.

The major underlying problems are: outmoded and inefficient boiler control strategies, and the inability to regulate the amount of heat provided at the point of use (the radiator).

Research is needed to establish optimum boiler control selection and operating strategies for older, multifamily buildings, verify the estimated savings associated with this technology, and characterize the factors that impact potential energy savings. The results of this work could be included in a future measuresguidelineon hydronic heating system retrofits for multifamily buildings.

We have found a number of articles describing technologies developed and results achieved. The data most valuable for us is presented in the table, describing the pre-existing control systems and retrofit measures.

Table 1. Existing and Planned Retrofit Controllers

The comparison of the systems having been tested allows to make the following conclusion: sabilling analysis based on this year’s utility bills (with new control system) and the previous years’ utility bills (with old control system) showed that the new control system saved a significant amount of space heating energy. After implementing control techniques, the overall weather-adjusted reduction in space heating gas consumption was 10.1% to–18.3% and averaged 15.2%.

The simple average payback is projected to be approximately 4.9 years. It should be noted that for the 2017–2018 heating season, the new control system was implemented gradually, only becoming fully functional in all buildings in April 2012. Therefore, it is expected that weather-normalized savings will be greater in future heating seasons.