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Looking for a Fast Payback by Installing a Dedicated Domestic Hot Water System? You May Want to Look Elsewhere

Installing a dedicated domestic hot water (DHW) plant is a common energy conservation measure (ECM) in the New York City multifamily market. According to Local Law 87 data, approximately 80% of the audited multifamily floor area uses steam heating boilers to produce domestic hot water.[1] A recent SWA analysis of data from steam buildings with tankless coils that implemented this ECM suggests that auditors may want to think twice about recommending this measure widely.

Two unsupported arguments are typically made in favor of installing a dedicated DHW system.

  1. A new condensing boiler or water heater (we will just say “water heater” here for simplicity and to distinguish the dedicated system from the heating boiler) will operate at a very high efficiency.
  2. Scotch marine steam boilers are inherently inefficient and are plagued with high standby losses. Large Scotch marine boilers fire to meet small DHW loads, and correctly sizing a new dedicated water heater will eliminate short cycling.

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Over Pressure (Part Two)

Welcome back! In Part One we talked about how steam pressure gets too much attention. Controlling pressure for its own sake should never be the end goal—steam pressure is just a means to an end. In this post we’ll discuss one way that controlling steam pressure can be useful—where it can help you balance the system, control the temperature, and yes, save energy.

Two-pipe Steam

The biggest issue plaguing two-pipe steam heating systems are steam traps. Steam traps are supposed to do just that—trap steam—keeping the pressurized steam on the supply side of the system and allowing air and water (i.e., condensate) to pass through into the returns. Keeping the supplies and returns separate is critical, but steam traps are too failure prone to accomplish this reliably.

Radiator steam “trap” failed open

Radiator steam “trap” failed open

At the start of any heating cycle, the system is full of air, which must be removed for steam to enter the heaters. In most two-pipe systems, the steam pushes the air out of the heaters, through the traps, and into the return piping where it eventually exits the system through a vent in a vacuum or condensate tank. That’s what happens when the traps are working. But a failed open trap is no trap at all. It lets the steam flow into the return piping and, with pressure on both the supply and return sides, air is trapped in the system. This affects those farthest from the boiler—the heaters near the ends of the mains and on the top floors—the most.  (And with air trapped inside keeping the metal cold, are they even heaters?)

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Electrify Everything? (part 1/?)

So in utility and policy circles, electrification is all the rage. Grid electricity is getting cleaner (i.e. resulting in lower CO2 emissions), on-site renewables are taking off (sometimes even with storage), and heat pump technologies are getting better. More regional and utility initiatives are encouraging building owners/designers/developers to forego onsite fossil fuels entirely (or at least mostly) to help meet CO2 emission reduction goals. But is electricity really more sustainable than natural gas? Is it cheaper? Which is better, really?

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VRF Systems vs. Electrical Resistance Heaters – A Case Study

Variable refrigerant flow (VRF), also known as variable refrigerant volume, was a concept developed by Daikin Industries in the 1980s. The technology is based on transferring heat through refrigerant lines from an outdoor compressor to multiple indoor fan coil units. VRF systems vary the amount of refrigerant delivered to each indoor unit based on demand, typically through variable speed drives (VFDs) and electronic expansion valves (EEVs). This technology differs from conventional HVAC systems in which airflow is varied based on changes in the thermal load of the space.

The two main VRF systems are heat pump systems that deliver either heating or cooling, or heat recovery systems that can provide simultaneous heating and cooling. These two applications, plus the inverter-driven technology of the outdoor compressors, allow for greater design flexibility and energy savings. In applications where heating and cooling are simultaneously called for in different zones, VRF heat recovery systems allow heat rejected from spaces that are being cooled to be used in spaces where heating is desired. Read more

Air-Source Heat Pumps in Cold Climates (Part II)

A few months ago I wrote about air-source heat pumps (ASHPs) in cold climates, and I promised more info on how to select the right systems and get the best performance. Below are some things we’ve learned from our work with ASHPs in the Northeast; much of this is based on the results from a study supported by the DOE Building America program. To be clear, we’re talking about inverter-driven (variable-speed) heat pumps in residential applications during heating season. Cooling is certainly important also, but we’ve been more focused on the heating performance, especially at lower temperatures. Read more